U.S. Department of the Interior
U.S. Geological Survey
Standards for the Analysis and Processing
of Surface-Water Data and Information
Using Electronic Methods
Water-Resources Investigations Report 01–4044
U.S. Department of the Interior
U.S. Geological Survey
Standards for the Analysis and Processing
of Surface-Water Data and Information
Using Electronic Methods
By V.B. Sauer
Water-Resources Investigations Report 01–4044
U.S. Department of the Interior
Gale P. Norton, Secretary
U.S. Geological Survey
Charles G. Groat, Director
U.S. Geological Survey, Reston, Virginia: 2002
For sale by U.S. Geological Survey, Information Services
Box 25286, Denver Federal Center
Denver, CO 80225
For more information about the USGS and its products:
Telephone: 1-888-ASK-USGS
World Wide Web: http://www.usgs.gov/
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply
endorsement by the U.S. Government.
Although this report is in the public domain, it contains copyrighted materials that are noted in the text.
Permission to reproduce those items must be secured from the individual copyright owners.
Library of Congress Cataloging-in-Publication Data
Suggested Citation: Sauer, V.B., 2002, Standards for the Analysis and Processing of Surface-Water Data and Inform-
ation Using Electronic Methods: U.S. Geological Survey Water-Resources Investigations Report 01–4044, 91 p.
iii
Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Surface-Water Data and Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3.2 Gage-Height Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.3 Velocity Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.4 Control Structure Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.5 Discharge Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.6 Field Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.7 Accuracy, Precision, and Significant Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Entry of Data to the Electronic Processing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1 Unit Value Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1 Sources of Unit Value Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.2 Unit Value Recording Time Interval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.3 Time System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.4 Standard Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 Field Measurement Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.1 Discharge Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2.1.1 Discharge Measurement Entry Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2.1.2 Numbering Discharge Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.2 Gage Datum Leveling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.3 Crest-Stage Gage Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2.4 Channel and Control Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2.5 Miscellaneous Field Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Verification and Editing of Unit Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1 Times and Dates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2 Time Corrections and Adjustments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2.1 Clock Error Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2.2 Universal Coordinated Time (UTC) Adjustments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3 Parameter Value Verifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3.1 Threshold Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3.2 Rating Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.3.3 Direct Reading Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.3.4 Graphical Comparisons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.4 Parameter Value Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.4.1 Datum Adjustments and Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.4.1.1 Adjustments For Gage Datum Error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.4.1.2 Conversion to NGVD or Other Datum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.4.2 Instrument Error Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.4.2.1 Constant Value Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.4.2.2 Parameter Variable Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
iv
5.4.2.3 Time Variable Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4.3 Numbering Correction Relations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4.4 Additive Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4.5 Identification of Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4.6 Flagging of unit values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6. Verification and Analysis of Field Measurement Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.1 Discharge Measurement Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.1.1 Arithmetic Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.1.2 Logic and Consistency Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.1.3 Computation of Measurement Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1.4 Shift Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1.4.1 Shifts for Stage-Discharge Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1.4.2 Shifts for Slope Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1.4.3 Shifts For Rate-of-Change In Stage Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.1.4.4 Shifts for Velocity-Index Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1.5 Special Procedures for Other Types of Discharge Measurements . . . . . . . . . . . . . . . . . . . . . . . . 29
6.1.5.1 Ice Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.1.5.2 Measurements With Vertical Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.1.5.3 Moving Boat Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.1.5.3.1 Moving Boat Measurement, Manual Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.1.5.3.2 Moving Boat Measurement, Automatic Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.5.4 Acoustic Doppler Current Profiler (ADCP) Measurements . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.5.5 Indirect Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.5.6 Portable Weir and Flume Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.5.7 Tracer-Dilution Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.5.8 Volumetric Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.1.5.9 Discharge Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.1.6 Rounding and Significant Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.1.7 Summary of Discharge Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.2 Gage Datum Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.2.1 Established Elevations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.2.2 Datum Error Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2.2.1 Base Benchmark Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2.2.2 Alternate Benchmark Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2.2.3 Rounding and Significant Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2.2.4 Gage Datum Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.3 Crest-Stage Gage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
6.3.1 Arithmetic Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.3.2 Logic and Consistency Comparisons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.3.3 Rounding and Significant Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.3.4 Summary of Crest-Stage Gage Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.4 Cross Sections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.4.1 Logic and Consistency Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.4.2 Graphical Review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.4.3 Computation of Cross-Section Hydraulic Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
v
6.4.4 Rounding and Significant Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7. Rating Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.1 Types of Rating Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.2 Rating Selection Default Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.3 Entry of Rating Curve Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.3.1 Tabular Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
7.3.2 Equation Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
7.3.3 Graphical Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.4 Rating Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.4.1 Interpolation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.4.2 Rating Table Precision and Significant Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.4.3 Rating Table Smoothness Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.4.4 Other Rating Table Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.5 Rating Curve Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.6 Updating and Renumbering Existing Rating Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7 Rating Curve Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7.1 Reversal of Ordinate and Abscissa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7.2 Electronic Processing System Monitor Plots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7.3 Paper Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7.4 Plotting Forms for Paper Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7.5 Linear Scale Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.7.5.1 Linear Scale Selection Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
7.7.5.2 Linear Scale Breaks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
7.7.6 Logarithmic Scale Plots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.6.1 Logarithmic Scale Selection Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.6.2 Scale Offsets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.6.2.1 Scale Offset Limitations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.6.2.2 Determination of Best Scale Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.6.3 Rating Curve Shaping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.7.7 Mathematical Fitting of Rating Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.7.8 Measurement Plotting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.7.8.1 Selection of Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.7.8.2 Selection of Independent Variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
7.7.8.3 Selection of Dependent Variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
7.7.8.4 Identification of Measurements on Rating-Curve Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7.7.8.5 Other Rating-Curve Plot Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7.8 Rating Curve Development Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7.8.1 Stage-Discharge Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7.8.1.1 Section Control Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7.8.1.2 Channel Control Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
7.8.1.3 Step-Backwater Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
7.8.2 Slope Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
7.8.3 Index Velocity Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
7.8.4 Rate-of-Change-in-Stage Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
8. Shift Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
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8.1 Shift Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
8.1.1 Input of Shift Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
8.1.2 Shift Curve Tables and Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
8.1.3 Period of Use for Shift Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8.1.4 Extrapolation of Shift Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8.2 Shift Curve Numbering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8.3 Shift Curve Error Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8.4 Shift Curve Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.4.1 Individual Shift Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.4.2 Multiple Shift Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.4.3 Additive Shift Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.4.4 Shift Interpolation Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.4.5 Rounding and Significant Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.4.6 Unit Value Graphical Comparisons of Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.4.7 Shift Curve Tracking Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
9. Primary Computations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
9.1 Unit Value Computations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
9.1.1 Stage-only Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
9.1.2 Stage-Discharge Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
9.1.3 Velocity Index Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
9.1.4 Slope Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
9.1.5 Rate-of-Change-in-Stage Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
9.1.6 Reservoir Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.1.7 Tide Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.1.8 Hydraulic Structure Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.1.9 BRANCH Model Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
9.2 Daily Value Computations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
9.2.1 Daily Mean Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
9.2.2 Daily Minimum and Maximum Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.2.3 Daily Values at Selected Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.2.4 Daily Values for Tidal Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.3 Summary of Primary Computations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
9.3.1 Unit Values Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
9.3.2 Primary Computations Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
9.3.3 Diagnostics Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
9.3.4 Daily Values Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
9.3.5 Unit Values and Discharge Measurement Comparison Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
10. Hydrograph Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
10.1 Unit Values Hydrographs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
10.2 Daily Values Hydrographs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
10.3 Supplementary Hydrograph Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
11. Computation of Extremes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
11.1 Annual Peak Stage and Discharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
11.2 Secondary Peak Stages and Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
11.3 Annual Minimum Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
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11.4 Summary of Annual Extremes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
12. Navigation Paths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
12.1 Basic Navigation Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
12.2 Navigating Through a Navigation Path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
12.3 Auxiliary Processing Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
13. Estimating Missing Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
13.1 Estimating Discharge Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
13.1.1 Hydrographic and Climatic Comparison Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
13.1.2 Discharge Ratio Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
13.1.3 Regression Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
13.1.4 Water-Budget Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
13.1.5 Mathematical Translation Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
13.1.6 Flow Routing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
13.2 Estimating Gage Height and Other Hydrologic Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
13.3 Comparison of Estimation Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
13.4 Flagging and Archival of Estimation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
14. Monthly and Annual Value Computations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
14.1 Monthly and Annual Values of Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
14.2 Monthly and Annual Values of Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
14.3 Monthly and Annual Values for Reservoirs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
14.4 Monthly and Annual Values for Tidal Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
15. Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
15.1 Record Processing Notebook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
15.2 Station Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
15.3 Station Analyses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
15.4 Station Manuscripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
16. Review, Approval, and Finalization of Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
17. Status of Data and Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
17.1 Original Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
17.2 Working Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
17.3 Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
17.4 Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
17.5 Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
18. Archiving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
19. Quality Assurance and Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
20. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
21. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
viii
Illustrations
1. Comparison of time system examples where daylight savings time is used . . . . . . . . . . . . . . . . . . . . . . . .20
2. Discharge measurement inside notes for manual type of moving boat measurement . . . . . . . . . . . . . .31
3. Example of a streamflow station datum summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
4. Typical stream cross-section plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
5. Example of expanded precision rating table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
6. Linear and log-log combination plotting form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
7. Typical rating curve, shift curve, shift table, and optional shift diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8. Example of shift-analysis table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
9. Example plot of time-series stage and shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
10. Example of a historical primary output of primary computations table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
11. Example of a standard primary output of primary computations table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
12. Basic navigation path requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79
Tables
1. Normal precision of measurements of surface water and related parameters . . . . . . . . . . . . . . . . . . . . . .5
2. Standard significant figures for surface-water data and information (English units) . . . . . . . . . . . . . . . . .6
3. Standard and daylight savings time zones of the United States and possessions. . . . . . . . . . . . . . . . . . . .9
4. Items to be entered to the electronic processing system from a discharge measurement
front sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
5. Items to be entered to the electronic processing system from the inside body of a discharge
measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
6. Items that may be entered to an electronic processing system from level notes. . . . . . . . . . . . . . . . . . . 16
7. Items that may be entered to an electronic processing system from crest-stage gage notes. . . . . . .17
8. Items that may be entered to an electronic processing system from cross-section notes . . . . . . . . . .17
9. Items that may be entered to an electronic processing system from miscellaneous field notes. . . . .18
10. Discharge measurement items that should be shown in U.S. Geological Survey long-form output
and in short-form output (historical form 9-207) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
11. Crest-stage gage items that should be shown in the summary output form . . . . . . . . . . . . . . . . . . . . . . . .40
12. Summary of calculated cross-section properties that should be listed in tabular format. . . . . . . . . . . .41
13. Rating curve characteristics, limitations, and requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
14. Parameters requiring daily maximum and minimum values computed for various station types . . . .67
15. Items required for primary output tables for various gaging station types. . . . . . . . . . . . . . . . . . . . . . . . . . .69
16. Items required for diagnostics tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74
ix
Conversion Factors and Datum
Multiply
By
To obtain
Length
inch (in.) 25.4x10
1
millimeter (mm)
inch (in.) 25.4x10
-2
meter (m)
foot (ft) 3.048x10
-1
meter (m)
mile (mi) 1.609x10
0
kilometer (km)
Area
acre 4.047x10
3
square meter (m
2
)
acre 4.047x10
-1
square hectometer (hm
2
)
acre 4.047x10
-3
square kilometer (km
2
)
square foot (ft
2
) 9.290x10
-2
square meter (m
2
)
square mile (mi
2
) 2.590x10
0
square kilometer (km
2
)
Volume
cubic foot (ft
3
) 2.832x10
1
cubic decimeter (dm
3
)
cubic foot (ft
3
) 2.832x10
-2
cubic meter (m
3
)
cubic foot per second day [(ft
3
/s)d] 2.447x10
3
cubic meter (m
3
)
cubic foot per second day [(ft
3
/s)d] 2.447x10
-3
cubic hectometer (hm
3
)
acre-foot (acre-ft) 1.233x10
3
cubic meter (m
3
)
acre-foot (acre-ft) 1.233x10
-3
cubic hectometer (hm
3
)
acre-foot (acre-ft) 1.233x10
-6
cubic kilometer (km
3
)
Flow rate
cubic foot per second (ft
3
/s) 2.832x10
1
liter per second (l/s)
cubic foot per second (ft
3
/s) 2.832x10
1
cubic decimeter per second (dm
3
/s)
cubic foot per second (ft
3
/s) 2.832x10
-2
cubic meter per second (m
3
/s)
Velocity
foot per second (ft/s) 3.048x10
-1
meter per second (m/s)
foot per hour (ft/hr) 3.048x10
-1
meter per hour (m/hr)
foot per hour (ft/hr) 2.54x10
1
millimeter per hour (mm/hr)
Sea level: In this report, “sea level” refers to the National Geodetic Datum of 1929 (NGVD of
1929)—a geodetic datum derived from a general adjustment for the first-order level nets of both
the United States and Canada, formerly called Sea Level Datum of 1929.
Standards for the Analysis and Processing
of Surface-Water Data and Information
Using Electronic Methods
by V.B. Sauer
Abstract
Surface-water computation methods and procedures are
described in this report to provide standards from which a com-
pletely automated electronic processing system can be devel-
oped. To the greatest extent possible, the traditional U. S. Geo-
logical Survey (USGS) methodology and standards for
streamflow data collection and analysis have been incorporated
into these standards. Although USGS methodology and stan-
dards are the basis for this report, the report is applicable to
other organizations doing similar work. The proposed elec-
tronic processing system allows field measurement data,
including data stored on automatic field recording devices and
data recorded by the field hydrographer (a person who collects
streamflow and other surface-water data) in electronic field
notebooks, to be input easily and automatically. A user of the
electronic processing system easily can monitor the incoming
data and verify and edit the data, if necessary. Input of the com-
putational procedures, rating curves, shift requirements, and
other special methods are interactive processes between the
user and the electronic processing system, with much of this
processing being automatic. Special computation procedures
are provided for complex stations such as velocity-index, slope,
control structures, and unsteady-flow models, such as the
Branch-Network Dynamic Flow Model (BRANCH). Naviga-
tion paths are designed to lead the user through the computa-
tional steps for each type of gaging station (stage-only, stage-
discharge, velocity-index, slope, rate-of-change in stage, reser-
voir, tide, structure, and hydraulic model stations). The pro-
posed electronic processing system emphasizes the use of inter-
active graphics to provide good visual tools for unit values
editing, rating curve and shift analysis, hydrograph compari-
sons, data-estimation procedures, data review, and other needs.
Documentation, review, finalization, and publication of records
are provided for with the electronic processing system, as well
as archiving, quality assurance, and quality control.
1. Introduction
The U.S. Geological Survey (USGS), Water Resources
Division (WRD), has been using automated data-processing
methods to compute, analyze, and publish surface-water
records since about 1963. Surface-water records, by definition,
generally include stage and streamflow of rivers, creeks, and
other streams; reservoir stage and contents; and tide stages in
and near the mouths of coastal streams. Prior to 1963, almost all
streamflow data were processed by hand and desktop calcula-
tors. After 1963, some of the processing steps, such as drawing
rating curves, were accomplished by hand methods and trans-
ferred to the computer by keying in the necessary values. The
first nationally used computer program for processing stream-
flow data was installed in 1972 and was part of the National
Water Data Storage and Retrieval System, referred to as WAT-
STORE (Hutchinson, 1977). In about 1983, a second program
referred to as the New Jersey District Automatic Data Recorder
(ADR) Processing System, or WRD Interim System, was used
nationally and essentially replaced the WATSTORE system.
The New Jersey System was installed for use on the Prime
Computers and was intended only for interim use until a new
program, the Automated Data Processing System, ADAPS
(Dempster, 1990), could be completed and installed. ADAPS
was installed nationally in 1985 and is part of the National
Water Information System (NWIS). In 1996–97, ADAPS was
converted to run on the Data General computer superseding the
Prime computer, and has since been further converted to run on
the Sun computer that superseded the Data General computer.
Instrumentation for the collection and field recording of
time-series data has attempted to keep pace with computer
capabilities for processing the data; however, a noticeable lag
has resulted. The evolution of data-collection methods shows a
progression from analog, or graphic, recorders to digital record-
ers, and finally to electronic data loggers and data-collection
platforms. Even so, many digital recorders still are in use as pri-
mary instruments, and many graphic recorders are in use as
backup instruments. Part of the reason for this is a lag in the
development and acceptance of electronic data loggers, and part
of the reason is lack of funds to support a full conversion. With
a mixture of instrumentation still in use, it becomes important
2 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
that data-processing software be able to accommodate the vari-
ous formats of input for time-series data.
Field measurements, such as discrete discharge determina-
tions, traditionally have been recorded on paper forms. This
form is still the accepted mode for these types of measurements.
However, electronic field notebooks have been developed that
may eventually become the standard for recording field notes
and measurements. Processing software must be able to accept
both types of input: keyboard entry from field notes recorded on
paper forms, and direct entry from electronic field notebooks.
In addition to changing instrumentation, increased capabil-
ities have developed for the analysis of streamflow information.
Traditionally, streamflow information is produced primarily
through the use of stage-discharge relations, with adjustments
to these relations for shifting controls. For some stations, more
complex computation procedures are used to account for vari-
able backwater and rate-of-change in stage. Structures, such as
dams, spillways, and turbines, are used at some stations to mea-
sure streamflow. The use of electromagnetic velocity meters
and acoustic velocity meters has increased our abilities to con-
tinuously monitor stream velocity, and, thereby, provide an
index of variable backwater. Unsteady-flow models, such as the
Branch-Network Dynamic Flow Model (BRANCH), by Schaf-
frannek and others (1981), also have been accepted as viable
methods to compute streamflow records. An unsteady-flow
model uses detailed hydraulic characteristics of a stream reach,
and has the capability to provide streamflow information at vir-
tually every location in the stream reach, which may extend for
many miles. This capability is a distinct advantage over the tra-
ditional gaging station that provides information at only one
location.
Another aspect of streamgaging and the production of
streamflow records is the increased need for streamflow infor-
mation on a real-time, or near-real-time, basis. This aspect has
led to remote sensing and transmitting systems where data are
received in the office within minutes, or at the most hours, of the
time of occurrence. These data usually are processed immedi-
ately upon reception in the office using automated computer
systems. In many instances, these same data are received by
agencies other than the USGS. Data and information of this type
should be classified as operational, having more uncertainty
than data and information that are subjected to verification,
interpretation, and review. Operational data and information
should not be considered the final answer for publication and
archiving.
The changing technologies of data collection and data pro-
cessing require changes in computer software. There is no
doubt that this will be a continuing process as new and better
computer technologies become available. In order to produce an
accurate and consistent data base, it is important that certain
procedures be standardized. The traditional hand methods, and
some of the more recent computer methods, have been
described in various USGS manuals, publications, and policy
memorandum. Probably the oldest and most well known of the
publications is Water Supply Paper 888 (Corbett and others,
1943). A recent update of that report is Water Supply Paper
2175 (Rantz and others, 1982). Two reports, "Computation of
Continuous Records of Streamflow" (Kennedy, 1983), and
"Discharge Ratings at Gaging Stations" (Kennedy, 1984) are
the most recent documentation of surface-water analysis proce-
dures. It is not the intent of this report to discount the applica-
bility or soundness of the above mentioned reports. In fact,
many of the field and office procedures, as well as the equip-
ment, described in those reports are still valid today. In particu-
lar, the concepts and theory of surface-water analysis are correct
and accepted. However, much of the information in those
reports apply to processing techniques where hand methods are
used either totally or partially. This report is intended to docu-
ment and establish a standard set of techniques for surface-
water data analysis and processing using electronic methods.
2. Purpose and Scope
The purpose of this report is to describe the standards to be
used in the automated processing of surface- water records by
computer. Although these standards are intended for use prima-
rily by the USGS, they may be used by other organizations
doing similiar work. By definition, surface-water records
include reservoir, stage-only, tide, and streamflow records. All
streamflow computation methods, including stage-discharge
relations, slope station method, index-velocity method, rate-of-
change in stage method, control structure methods, and
unsteady-flow model methods are described in this report. The
emphasis of the report concerns automated, electronic process-
ing and analysis, but by necessity, user interaction is required to
provide the necessary interpretation and quality control.
3. Surface-Water Data and Information
Surface-water data and information are composed of a
number of measured and computed variables. This section of
the report will describe some of these, and will define some of
the terminology used throughout the report. These definitions
should become part of the standards, just as the methodology is
part of the standards.
3.1 Definitions
The words data and information, as used in this report, are
intended to have special meanings. The term data is used for the
results obtained from the measurement of a basic variable,
which cannot be repeated. Data can be accepted, qualified, or
rejected, but they cannot be modified without compromising
their identity as data. Any change or modification of a data
value converts that value into information. For example, if an
original measurement of gage height is corrected for sensor
error (such as drift related to time, gage height, temperature, or
other factors), the new value of gage height is information.
3. Surface-Water Data and Information 3
Another example would be the use of a gage-height value and a
relation of gage height to discharge, to compute a value of dis-
charge. The computed discharge value is information. Unlike
data, information can be modified, as would be the case if a
stage-discharge relation were revised. Data generally are
treated as a primary record, whereas information usually is
treated as a secondary record.
The term unit value is used to denote a measured or com-
puted value that is associated with a specified instantaneous
time and date. In addition, unit values generally are part of a
time-series data set. For surface-water records, unit values for
all parameters always should be instantaneous values. Some
parameters, such as velocity, tend to fluctuate rapidly and a true
instantaneous value would be difficult to use in the analysis and
processing of the records. Some instruments are designed to
take frequent (for example, every second) readings, temporarily
store these readings, and then compute and store a mean value
for a short time period. For these situations, the field instru-
ments should be programmed to record mean unit values for
very short time intervals (1 to 2 minutes) so they can be consid-
ered for practical purposes to be instantaneous unit values.
Daily values are measured or computed values of a param-
eter for a specific date only. The time of the daily value is not
required, although for certain daily values, time sometimes is
stated. Examples of daily values are daily mean value, maxi-
mum instantaneous value for a day, and minimum instanta-
neous value for a day. In the case of maximum and minimum
instantaneous values for a day, the time of the value usually is
stated.
A hydrographer is defined for purposes of this report to be
a person who collects streamflow and other surface-water data
in the field. A user is a person who uses the electronic process-
ing system to input data, analyze data, and process streamflow
and other surface-water data and information. In many cases,
the hydrographer and user may be the same person, but some-
times may be different persons.
3.2 Gage-Height Data
The height of the surface of a water feature, such as a
stream, reservoir, lake, or canal, usually is referred to as gage
height, stage, or elevation. For a streamgaging station, gage
height is the more appropriate terminology, but the more gen-
eral term “stage” is sometimes used interchangeably (Langbein
and Iseri, 1960). For lakes, reservoirs and tidal streams, the
height of the water surface usually is referred to as elevation.
Gage height (also stage) is measured above an arbitrary gage
datum, whereas elevation is measured above National Geodetic
Vertical Datum (NGVD). Gage heights and elevations are prin-
cipal data elements in the collection, processing, and analysis of
surface-water data and information. Gage heights and eleva-
tions are measured in various ways, such as by direct observa-
tion of a gaging device, or by automatic sensing through the use
of floats, transducers, gas-bubbler manometers, and acoustic
methods. Gage heights and elevations should be measured and
stored as instantaneous unit values. Subsequent data processing
and analysis will provide the means for any required analysis,
such as averaging.
3.3 Velocity Data
Another data element in a streamgaging system is stream
velocity. Unit values of stream velocity are measured at some
sites for the purpose of computing stream discharge where vari-
able backwater conditions are present. The three principal
instruments for measuring stream velocity are the deflection
vane gage, the electromagnetic velocity meter, and the acoustic
velocity meter. The methods for using each of these to compute
stream discharge will be described in section 9.1.3. For pur-
poses of definition, the deflection vane gage readings are
simply an index of stream velocity, whereas the electromag-
netic and acoustic meters provide actual velocity readings.
Deflection vane gage readings are instantaneous values. Elec-
tromagnetic and acoustic velocity readings usually are recorded
as an average of a number of instantaneous readings. The aver-
aging period should be short, on the order of 1 or 2 minutes. The
recording interval is determined by the site characteristics and
the flashiness of the stream. For example, a typical electromag-
netic or acoustic gage setup may compute 1 minute averages of
stream velocity every 15 minutes and record these as instanta-
neous readings. The instrument would be active for 1 minute,
and idle for 14 minutes.
3.4 Control Structure Data
Control structures, for the purpose of this report, are
defined as manmade structures that are used to control the flow
of water in a river or stream. These structures are located mostly
at dams. A number of devices, such as free-flow spillways,
gated spillways, sluice gates, turbines, pumps, siphons, and
navigation locks convey flow through, over, and/or under a
structure. In many cases, these can be instrumented and cali-
brated so that the stream discharge can be accurately deter-
mined. At a control-structure streamgage site, instrumentation
may be required to record unit values of headwater gage height,
tailwater gage height, gate openings, turbine pressures, lock-
ages, and other variables that relate to the flow through the
structure. A control structure is frequently a very complex
system requiring numerous instruments and sensors to accu-
rately measure the flow. A special computer program is part of
the control-structure system and is used to process the structure
data and compute discharge.
3.5 Discharge Information
A very important element, and frequently the ultimate goal
in streamgaging, is the determination of stream discharge. Dis-
charge cannot be measured directly, but must be computed from
other measured variables such as gage height, stream depth,
4 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
stream width, and stream velocity. Therefore, discharge is con-
sidered to be information rather than data. It is common practice
to compute instantaneous unit values and daily mean values of
discharge for gage sites. Instantaneous unit values of discharge
are computed from various types of relations, such as a stage-
discharge relation, a stage-area-velocity-discharge relation, or a
stage-fall-discharge relation. Other relations might involve rate-
of-change in stage, unsteady-flow models, and various struc-
tures such as gates, turbines, navigation locks, pumps, and
siphons. Each of these computational procedures will be dis-
cussed in subsequent parts of this report.
Daily mean values of discharge are computed from instan-
taneous unit values of discharge. This method differs from
some of the methods used in the past where daily mean values
of discharge were computed from daily mean values of gage
height. It also differs from procedures where mean values of
gage height for subdivided parts of a day were used to compute
discharge. The procedure for computing daily mean values of
discharge from instantaneous unit values is described in section
9.2.
3.6 Field Measurements
Various kinds of data and information that are needed for
the calibration and maintenance of a streamgaging station are
obtained from field measurements. Most notable of these field
measurements is the current meter measurement that is obtained
periodically to define and check the discharge rating curve.
Other types of field measurements include gage-datum level-
ing, indirect discharge measurements, and crest-stage gage
measurements. Various measurements, other than discharge,
and gage inspection notes sometimes are made and reported on
field note sheets. For some stations with special methods for
determining discharge, field measurements will be made of
stream cross sections, estimates of stream roughness coeffi-
cients, and details of structures such as spillways, gates, and
others. It is beyond the scope of this report to describe the
details of most field measurements, but the surface-water anal-
ysis and processing system must provide an efficient method for
entry and use of the field data and information.
3.7 Accuracy, Precision, and Significant Figures
Accuracy, precision, and significant figures are terms that
are often confused and misinterpreted. This section of the report
will describe the meanings of these terms, and provide a stan-
dard for use with surface-water data and information.
Accuracy is defined as the closeness or agreement of a
measurement to the absolute or true value. Precision, refers to
the closeness or agreement of repeated measurements to each
other. Thus, precision also refers to the degree of refinement
with which a measurement is made and repeated. An accurate
measurement also is a precise measurement, but a precise mea-
surement is not necessarily an accurate measurement. For
example, a person making a measurement of gage height by
using a wire-weight gage carefully can perform all techniques
for setting the weight at the exact water surface, carefully can
read the gage dials, and can repeat the measurement a number
of times. The average reading obtained is a very precise mea-
surement of gage height. The reading may not be accurate, how-
ever, because error may be present in the wire-weight gage
mechanism, or expansion/contraction error in the cable, or error
in the datum setting of the gage, or a combination of these
errors.
Accuracy and/or precision also may vary according to the
magnitude of the measurement being made. Again, using the
measurement of gage height as an example, a gage reading at
low values may be more precise than a gage reading at high
values because the water surface may have more surging and
wave action at high values. Accuracy also may be different
between high and low values because gage-datum setting, or
other gage errors, may be different at high and low values.
Another way of expressing accuracy and precision is from
a statistical point of view. If an observer makes a number of
readings of a gage over a very short time period (minutes), and
during a time when the stream stage is not changing, then theo-
retically the same gage height is measured each time the gage is
read, assuming the equipment is in perfect working order,
including the observer’s ability to read the gage. Because equip-
ment and people are not perfect, the gage readings will not
always be the same. A statistical measure of the dispersion or
scatter of the gage readings is defined as precision. Generally,
the statistical measure used is the standard deviation, or the
spread of about two-thirds of the readings. Precision, or lack of
precision, is a random error having both plus and minus devia-
tions. Averages of individual readings usually have less scatter
than individual readings. Thus, the precision can be increased
by averaging readings. However, averaging does not totally
eliminate scatter and, thus, even the average has limited preci-
sion.
The preciseness of a gage reading, as described above, is
not the sole measure of the accuracy of the reading. For exam-
ple, if the cable of a wire-weight gage is longer or shorter
because of an uncorrected temperature difference, then this
error affects all gage readings during the short time period in
question. Averaging does not remove this error, because all of
the gage readings are affected by it with exactly the same mag-
nitude and sign. Such errors, which do not change during a
series of repeated gage readings, and that are not reduced by
averaging, are called systematic errors or biases.
Accuracy is expressed in terms of the difference between
a measurement result (whether a single measurement or the
mean of various measurements) and the true gage height. The
measurement result can differ from the true value because of
random errors (precision) or systematic errors (bias), or both.
Accuracy, or more properly, its obverse, uncertainty, normally
is expressed as the square root of the sum of squares of standard
deviation of random errors plus the sum of squares of estimated
systematic errors. A discussion of accuracy is given also by
Rantz and others (1982).
3. Surface-Water Data and Information 5
The precision of various types of measurements necessary
for processing surface-water records is given in table 1. The
value given for each parameter is not based on a statistical anal-
ysis, but has been based on experience and commonly accepted
precision used for surface-water analysis. For instance, it com-
monly is accepted that gage heights can be measured to a preci-
sion of 0.01 ft. Gage heights may not be that accurate, although
if gages are maintained properly, and gage datum is checked
and maintained carefully, it generally is accepted that gage-
height accuracy can be within 0.01 ft at most sites. Some sites
where conditions are not conducive to precise measurement of
gage height may require that gage-height precision be as low as
0.1 ft.
Table 1. Normal precision of measurements of surface water and related parameters
[ft, feet; ft/s, feet per second]
Parameter
Precision of Measurements
English Units Metric Units
Gage height or elevation of water surface 0.01 ft 0.001 meter
Gage height of zero flow, natural channel .1 ft .01 meter
Gage height of zero flow, manmade control structure .01 ft .001 meter
Gage height of gage features .01 ft .001 meter
Velocity (Electromagnetic meter (EM), ultrasonic velocity meter (UVM), Price
current meter)
.01 ft/s .001 meters per second
Depth (uneven streambed, deep streams) .1 ft .01 meter
Depth (smooth streambed, shallow streams) .01 ft .001 meter
Width (wading measurements, narrow cross sections) .1 ft .01 meter
Width (bridge, cable, boat, wide cross sections) 1 ft .1 meter
Ground elevation (cross section) .1 ft .01 meter
Reference and benchmarks .001 ft .001 meter
6 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
A third term to be defined is significant figures. As the
name implies, a significant figure is a figure that expresses
meaning, and can aid in evaluating the accuracy of a value.
Every digit in a number is considered significant except zeros
that are added for the purpose of locating the decimal. Zeros
usually are not considered significant when they are to the
extreme right of a number but to the left of the decimal, and
when they are at the extreme left of a number. Zeros to the
extreme right of a number and to the right of the decimal are
considered significant because they are not needed to locate the
decimal. All zeros that are between other digits are considered
significant.
For surface-water records, the standards for significant fig-
ures have been established and accepted for most of the data and
information values used (table 2). Exceptions to the standard
significant figures can be made when conditions warrant. For
instance, a daily mean discharge greater than or equal to 100 ft
3
/
s usually is shown to three significant figures, but an estimated
daily mean discharge might not be considered accurate to more
than two significant figures, or in some cases even one signifi-
cant figure. Such a reduction in the number of significant fig-
ures implies a reduction in the accuracy of the value.
Table 2. Standard significant figures for surface-water data and information (English units)
[x = significant figure, 0 = nonsignificant figure]
Data or Information Value Significant Figures
Water-surface gage height and elevation .0x, .xx, x.xx, xx.xx, xxx.xx, xxxx.xx
Stream depth .0x, .xx, x.x, xx.x xxx.
Stream width .xx, x.x, xx., xxx., xxxx., xxxx0.
Cross-section area .xx, x.x, xx.x, xxx., xxx0., xxx00., xxx000.
Cross-section conveyance x., xx., xxx., xxx0., xxx00., xxx000., xxx0000.
Stream velocity (mean or instantaneous) .0x, .xx, x.xx, xx.xx
Velocity adjustment factor (index-velocity) .0x, .xx, x.xx
Boyer factor (1/US
c
) .0x, .xx, x.xx
Reservoir contents xxxx., xxxx0., xxxx00., xxxx000., and so forth
Stream discharge (daily mean) .0x, .xx, x.x, xx., xxx., xxx0., xxx00., xxx000., xxx0000.
Stream discharge (measurement) .0xx, .xx, x.xx, xx.x, xxx., xxx0., xxx00., xxx000., xxx0000.
Water-surface fall (slope stations) .0x, .xx, x.xx, xx.xx
Fall ratio (slope stations) .0x, .xx, x.xx
Discharge ratio (slope stations) .0x, .xx, x.xx
Gage height of zero flow .0x, x.xx, xx.xx
Gage height of high water marks .xx, x.xx, xx.xx, xxx.xx
Gage height of gage features .xx, .xx, x.xx, xx.xx, xxx.xx
Reference and benchmark elevations .00x, .0xx, .xxx, x.xxx, xx.xxx, xxx.xxx, xxxx.xxx
Control structure elevations and gage heights .0x, .xx, x.xx, xx.xx, xxx.xx
Natural ground elevations and gage heights .x, x.x, xx.x, xxx.x
4. Entry of Data to the Electronic Processing System 7
4. Entry of Data to the Electronic Processing
System
The first step required for the processing of surface-water
data is the entry of field data and information to the electronic
processing system. This processing will include unit value data
and field measurement data and information. Field measure-
ment data can include discharge measurement data and infor-
mation, gage-datum leveling data, crest-stage gage data, chan-
nel and control cross-section data, and other miscellaneous
data, information, and notes.
4.1 Unit Value Data
The recording of unit value data has evolved from simple
hand written notes, to analog recorders, to digital recorders, to
sophisticated programmable data loggers, and to direct data
transmission to the computer by radio, telephone, or satellite.
Although the trend today is toward the use of programmable
data loggers and direct data transmission, digital recorders still
are widely used, and some use of analog recorders and hand
written observer records. Therefore, the electronic processing
system must accommodate each of these types of data formats.
Preparation of unit value data for electronic processing
should follow a basic sequence. However, because different
methods are available for collecting and recording field data,
there may be instances where the preferred sequence cannot be
followed. The following sequence is advised:
1. A copy of the original, unedited unit values should be
stored (archived) before any editing, conversions, or com-
putations are made. All editing, conversions, and computa-
tions should be performed using an electronic copy of the
original data.
2. The unit values should be translated into a standard format
(see section 4.1.4).
3. The unit value times should be corrected for clock errors,
if applicable (see section 5.2).
4. Conversions to UTC time should be made (see section 5.2)
so that all unit value data can be related to standard time or
daylight savings time, as required.
5. The unit values prepared in this manner then can be used
for all further computations, analysis, and archiving, as
described in this report.
Various types of unit value data can be entered into the
electronic processing system. These data include unit values of
gage height (stage or elevation), velocity or velocity index,
spillway gate opening or index, turbine pressures, navigation
lockages, and other readings associated with structures. For
some gage sites, multiple data sets of unit values may be avail-
able for a given parameter. For instance, a stream affected by
backwater may have two gages at different locations for the pur-
pose of measuring gage height. Unit values of gage height
(stage or elevation) is a mandatory entry for each gage site.
4.1.1 Sources of Unit Value Data
A brief description of the six methods of obtaining, record-
ing, and entering unit value data to the electronic processing
system is given in the following paragraphs. Each set of unit
values must be identified as to the source and method of aquisi-
tion.
Observer data—At some gage sites, gage readings are
made by an observer. These readings are recorded, along with
date and time of the reading, on a preprinted form. Such read-
ings may be used as the primary set of unit values for the station,
or they may be used only for backup and verification of another
measuring and recording method. The hand written unit values
made by an observer must be entered into the electronic pro-
cessing system by direct keyboard entry. The date and time
must be entered for each unit value, and the time zone designa-
tion must be entered for each set of unit values.
Analog recorders—Analog, or graphical, recorders are
frequently used to record the gage height, or other parameters,
as sensed by a float, pressure system, or other measuring device
connected to the recorder. Analog recorders provide a continu-
ous trace of the measurements on a graphical chart that is driven
by a clock to provide a time scale. Unit value data from these
charts are entered to the electronic processing system through
the use of an automatic, or hand operated, digitizer. The digi-
tizer enters unit values from the chart at time intervals specified
by the user. Beginning and ending dates and times, and the time
zone designation, must be entered for each segment of chart that
is digitized. Analog records may be used as the primary unit
values for a station, but are more frequently used for backup and
verification of unit values collected with a different method.
Automated digital recorders—The automated digital
recorder (ADR) is a device that records data on a narrow paper
strip by punching a series of holes that digitally are coded to
represent the unit value reading. The paper strip advances after
each punch and data are recorded at a specified time interval,
commonly 5, 15 or 60 minutes. Other time intervals may be
used in some instances, but the time interval is uniform for each
gage. Unit value data are entered to the electronic processing
system by passing the paper strip through a digital tape reader.
Starting and ending dates and times, and the time zone designa-
tion, must be entered for each processing period. ADR's fre-
quently are used as the primary recording instrument for a gage
site, but also are used as backup and verification for other types
of instruments.
Electronic data loggers—Various types of electronic data
loggers are in use for recording unit value data. These devices
receive data from a sensing instrument and record the unit value
in electronic memory. Data are extracted from the data logger
either by removing the memory chip or by reading data from the
memory into an external storage module or field computer.
Because of the many configurations and types of data loggers
8 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
currently in use, and because changes occur frequently, it is not
practical to attempt a description in this report. The process of
entering data from these types of recorders primarily is elec-
tronic. Electronic data loggers have the advantage over analog
recorders and ADR’s because they can be programmed to sense
and record according to pre-defined rules, as discussed in sec-
tion 4.1.2. A recording system of this type results in a variable
time interval between unit values, and necessitates the record-
ing of the time and date associated with each unit value. If the
recording time interval is constant, then most electronic data
loggers do not record the time and date associated with each
unit value. For either method, variable or constant recording
interval, the starting and ending date and time must be entered
for the period of record being processed. Electronic data loggers
frequently are used for the primary recording instrument, but in
some cases they may be used only for backup and verification.
Data-collection platforms—Data-collection platforms
(DCP's) are field systems whereby data are stored electronically
for a relatively short time (from 2 to 4 hours) and then transmit-
ted by radio, telephone, or satellite to an office computer. For
some types of DCP's, storage may be comparable to an elec-
tronic data logger and the data can be retrieved in similar fash-
ion. DCP's are frequently operated in conjunction with an elec-
tronic data logger, ADR, or analog recorder. A variety of gage
and recorder configurations is possible. Where two or more
recorders are used, one should be designated the primary instru-
ment, and the DCP frequently is given that distinction. In some
instances, the DCP is the only instrument used and the primary
record is received directly in the office. Unit value data trans-
mitted and received by satellite automatically are tagged with
date and time, which is determined from Universal Coordinated
Time (UTC).
Other—Unit value data that are stored on other computer
systems can be transferred to the electronic processing system
by use of card images or other standard data formats.
One of the recorder types described above usually is des-
ignated as the primary recorder for computing the primary
records of gage height, discharge, reservoir contents, or other
parameters. Frequently, a second recorder is operated in con-
junction with the primary recorder, and is designated the
backup recorder. In the event of the malfunction of the primary
recorder, the electronic processing system should allow the
entry of unit values from the backup recorder as a substitute for
the primary recorder values. These substitute unit values should
be identified with a flag as to the source of the backup records.
These records also should be subject to all further analysis, such
as time corrections, parameter value corrections, and others, as
described in section 5.
4.1.2 Unit Value Recording Time Interval
The time interval between recorded unit values may be a
constant value, or the time interval may be variable. The pro-
grammable data logger allows the recording interval to be
varied according to user- specified rules. The variable time
interval can be based on the value of the parameter being
recorded, the time length since the last recording, the rate of
change of the parameter value being recorded, the value or rate
of change of some other parameter, or some combination of
these. The electronic processing system can accommodate
either method of data recording, constant or variable time inter-
val.
4.1.3 Time System Requirements
The time system used in most field data-collection systems
is based on the local time in use at each gaging location. For
most parts of the United States, the local time is a changing time
system where the clock is advanced 1 hour in the spring, and set
back 1 hour in the fall. The time during the summer period com-
monly is referred to as daylight savings time, and the remainder
of the year as standard time. The advent of the satellite data col-
lection platforms (DCP) has required the use of Universal Coor-
dinated Time (UTC) for DCP field instruments. Additionally,
some gage sites are operated year around on local standard time
without making the change for daylight savings time. Conse-
quently, there is a mixture of time systems being used for col-
lection and recording of surface-water data. The surface-water
electronic processing system must accommodate the entry of
data in any of the time systems. Therefore, all data entry must
include a designation of the time system at which the data were
recorded. Time system designations will be an acronym based
on the time zone, or time system, to which the gage is operated.
Standard and daylight savings time zones, and the UTC offset,
for the United States and possessions are shown in table 3.
4. Entry of Data to the Electronic Processing System 9
All times, both for time series data and for measurement
data, automatically will be converted to UTC time for storage
within the electronic processing system. Therefore, time adjust-
ments for the 1-hour daylight savings time offset automatically
will be accounted for when times are converted to UTC. The
user will be able to perform computations, such as for daily
mean values of streamflow, using any specified time system.
The electronic processing system automatically will make the
necessary time conversions, including changes between stan-
dard and daylight savings times, prior to making the computa-
tions. Likewise, unit values of gage height, discharge, or other
parameters, would be retrieved using a time system of the user's
choice.
4.1.4 Standard Format
All unit value data stored in the electronic processing
system should conform to a standard unit value format. This
format essentially means that the electronic processing system
should convert all unit values to engineering units, including a
decimal, and assign times and dates based on the time system
used for field recording of data. Time adjustments for the pur-
pose of converting the unit value times to standard UTC time
are made automatically. Time corrections made for clock errors
should be made after the data are converted to a standard for-
mat. Parameter value corrections are made on the basis of user
instructions after data are entered to the electronic processing
system. Additional details regarding time and parameter cor-
rections are described in section 5.
4.2 Field Measurement Data
Various types of field measurements are made at surface-
water gaging stations, each providing various kinds of data and
information. These include measurements of stream discharge,
leveling for gage datum checking, crest-stage gage measure-
Table 3. Standard and daylight savings time zones of the United States and
possessions
Designation Time Zone Name
1
UTC Offset
2
(hours)
UTC Universal Coordinated Time 0
AST Atlantic Standard Time + 4
ADST Atlantic Daylight Savings Time + 3
EST Eastern Standard Time + 5
EDST Eastern Daylight Savings Time + 4
CST Central Standard Time + 6
CDST Central Daylight Savings Time + 5
MST Mountain Standard Time + 7
MDST Mountain Daylight Savings Time + 6
PST Pacific Standard Time + 8
PDST Pacific Daylight Savings Time + 7
YST Yukon Standard Time + 9
YDST Yukon Daylight Savings Time + 8
AHST Alaska-Hawaii Standard Time +10
BST Bering Standard Time +11
BDST Bering Daylight Savings Time +10
1
Time zone names and designations not defined for the United States Trust Territory west of
the international date line, where UTC offsets vary from -10 to -12 hours.
2
UTC offsets are added to the standard and daylight savings local times to obtain Universal
Coordinated Time (UTC)
10 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
ments, channel and control cross-section measurements, and
other miscellaneous data and information. Usually, each type of
field measurement is recorded on a form designed especially for
that type of measurement. The electronic processing system
should be able to receive, process, and store the field measure-
ment data and information so the data can be used in other parts
of the electronic processing system.
Most field data are recorded on paper forms and must be
transferred to the electronic processing system by keyboard
entry. Field data and information that are recorded electroni-
cally in a field computer will require an interface between the
field computer and the office computer to transfer the data auto-
matically.
4.2.1 Discharge Measurements
The electronic processing system should have the capabil-
ity to receive and store essentially all of the data and informa-
tion recorded on discharge measurement note sheets. This
capability would include the information shown on the front
sheet of the notes and the detailed measurement data shown in
the body of the notes. In the case where discharge measure-
ments and associated information are recorded in electronic
field computers, the electronic processing system would receive
the data and information automatically through an interface.
Although the electronic processing system should be able
to receive all data (front sheet and inside body) from a discharge
measurement recorded on paper forms, it is not mandatory that
the inside body data and information be entered. This part of the
measurement is not normally used in the processing of daily
discharge records. The main purpose for entering the data and
information from the inside body would be for computational
checking (see section 6.1), and for special studies.
The original measurement is either the data and informa-
tion recorded on paper notes, or the data and information
recorded in an electronic field notebook. If the measurement
was recorded on paper, those original paper notes are saved for
archival. If the measurement was recorded electronically, the
first electronic copy entered to the electronic processing system
becomes the archival copy. For this reason, it is mandatory that
the entire measurement recorded in an electronic field note-
book, including all of the individual data elements, be entered
in the electronic processing system. Additional information
about archiving requirements can be found in section 17.
4.2.1.1 Discharge Measurement Entry Requirements
Discharge measurement data will be acquired from 1 of 10
different methods of measurement. These methods include
1. standard current meter measurements (wading, bridge-
board, handline, bridge crane, cableway, and stationary
boat),
2. ice measurements,
3. moving boat measurements (manual and automated),
4. acoustic Doppler profiler measurements (ADCP),
5. tracer-dilution measurements,
6. portable weir and flume measurements,
7. indirect measurements (slope area, contracted opening,
culvert, stepbackwater, and critical depth),
8. surface velocity measurements (timing of floats or drift,
optical, and others),
9. volumetric measurements, and
10. simple estimates of discharge.
The input forms presented to the user with the electronic
processing system should be designed to conform with the mea-
surement method. That is, the input form for measurement sum-
mary information for a specific method of measurement (for
example, portable flume) would have input items specific to
that method of measurement, and would omit input items that
are not applicable to that method of measurement. Data-entry
requirements for entry of summary information for discharge
measurements, according to the method of measurement are
listed in table 4.
The specific measurement data on the inside of the dis-
charge measurement, although not mandatory, would be
entered on separate input forms. The data and information
required for these forms are listed in table 5. For some measure-
ment methods the inside data may require multiple entries of
some items.
4. Entry of Data to the Electronic Processing System 11
Table 4. Items to be entered to the electronic processing system from a discharge measurement front sheet
Item
Number
Measurement
Item
Discharge Measurement Method
Standard Current Meter
Ice
Moving Boat (Manual and Automated)
Acoustic Doppler Current Profiler
Dye Dilution
Portable Weir or Flume
Indirect
Surface Velocity
Volumetric
Estimate
1
1 Station identification number XXXXXXXXXX
1
2
Station name (Obtain from site file, if
available)
X X X X X X X X X X
1
3 Measurement type
1
XXXXXXXXXX
1
4 Measurement sequence number X X X X X X X X X
1
5 Party XXXXXXXXXX
1
6 Start date (date of flood for indirects) X X X X X X X X X X
7 End date XXXXXX XXX
8 Start time X X X X X X X X X
9 End time XXXXXX XXX
10 Time zone X X X X X X X X X X
11 Gage readings (table) XXXXXX XXX
1
12 Mean gage height, Inside Gage X X X X X X X X X X
13 Mean gage height, Outside Gage XXXXXXXXXX
14 Gage-height change X X X X X X X X X
15 Gage-height change time XXXXXX XXX
16 Mean index velocity X X X X X X X X X X
17 Mean auxiliary gage height XXXXXXXXXX
18 Stream width X X X X X
19 Stream area XXXX X
20 Mean velocity X X X X X
21 Number of sections XXXX X
1
22 Measured discharge X X X X X X X X X X
23 Channels measured XXXXXXXXXX
24 Adjusted discharge X X X X X X
12 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
25 Adjustment method
2
XXXXX X
26 Measurement location
2
X X X X X X X X X X
27 Current meter type
2
XXX X
28 Current meter number X X X X
29 Initial current meter inspection X X X X
30 Final current meter inspection X X X X
31 Suspension method
2
XX X
32 Observation method
2
X X X
33 Description of measuring section XXXXX X X
34 Flow conditions
2
X X X X X X X
35 Horizontal angle coefficient X X X
36 Method coefficient
2
X X X X
37 Suspension coefficient
2
XX
38 Average time for point velocities X X X
39 Accuracy rating
2
XXXXXXXXXX
40 Computed accuracy X
41 Control description
2
XXXXXXXXXX
42 Control conditions
2
X X X X X X X X X X
43 Control cleaned X X X X X X
44 Time of control cleaning X X X X X X
45 Gage-height change from cleaning X X X X X X
46 Maximum stage indicator X X X X X X X X X
47 Minimum stage indicator XXXXXX XXX
48 Highwater marks
2
X X X X X X X X X X
49 Air temperature XXXXXX XXX
Table 4. Items to be entered to the electronic processing system from a discharge measurement front sheet—Continued
Item
Number
Measurement
Item
Discharge Measurement Method
Standard Current Meter
Ice
Moving Boat (Manual and Automated)
Acoustic Doppler Current Profiler
Dye Dilution
Portable Weir or Flume
Indirect
Surface Velocity
Volumetric
Estimate
4. Entry of Data to the Electronic Processing System 13
Table 5. Items to be entered to the electronic processing system from the inside body of a discharge measurement
Discharge Measurement Method
Item
Number
Measurement Item
Standard Current Meter
Ice
Moving Boat (Manual Only)
1
Acoustic Doppler current profiler
1
Dye Dilution
2
Portable Weir orFflume
Indirect
2
Surface Velocity
Volumetric
Estimate
2
3
1 Station identification number X X X X X X
3
2 Station Name X X X X X X
3
3 Measurement sequence number X X X X X X
4 Channel number or name X X X X X X
5 Distance from initial point X X X X
6 Subsection width X X X
7 Horizontal angle coefficient X X X
8 Depth, water surface to streambed X X X X
50 Water temperature X X X X X X X X X
51 Base flow
2
XXXXX
52 Gage height of zero flow X X X X X X
53 Gage height of zero flow accuracy X X X X X X
54 Remarks, written comments X X X X X X X X X X
1
Mandatory.
2
Requires supplementary table or menu selections.
Table 4. Items to be entered to the electronic processing system from a discharge measurement front sheet—Continued
Item
Number
Measurement
Item
Discharge Measurement Method
Standard Current Meter
Ice
Moving Boat (Manual and Automated)
Acoustic Doppler Current Profiler
Dye Dilution
Portable Weir or Flume
Indirect
Surface Velocity
Volumetric
Estimate
14 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
9 Velocity observation depth(for example, .2,
.6, .8, Surface)
XX X
10 Current meter revolutions X X X
11 Time of current meter revolutions X X X
12 Velocity at point X X X
13 Mean velocity in vertical X X X X
14 Subsection area X X X
15 Depth, water surface to bottom of ice X
16 Effective depth X X
17 Air line distance (for vertical angle correc-
tions)
X
18 Vertical angle X
19 Horizontal angle, manual moving boat X
20 Pulses per second X
21 Boat travel distance X
22 Vector velocity X
23 Sine of horizontal angle X
24 Subsection discharge X X X
25 Surface velocity measuring distance X
26 Surface velocity travel time X
27 Surface velocity X
28 Total container volume X
29 Starting volume X
30 Ending volume X
31 Flow volume (difference of start and end
volumes
X
32 Fill time X
Table 5. Items to be entered to the electronic processing system from the inside body of a discharge measurement—Continued
Discharge Measurement Method
Item
Number
Measurement Item
Standard Current Meter
Ice
Moving Boat (Manual Only)
1
Acoustic Doppler current profiler
1
Dye Dilution
2
Portable Weir orFflume
Indirect
2
Surface Velocity
Volumetric
Estimate
2
4. Entry of Data to the Electronic Processing System 15
33 Total volume (sum of flow volumes) X
34 Total time (sum of fill times) X
35 Subsection number (items 35-39 for volu-
metric-incremental method)
X
36 Subsection width X
37 Sample width X
38 Subsection/sample width ratio X
39 Subsection discharge X
40 Head X
41
Average head X
42
Total width
X X X X
43
Total area X X X X
44
Total discharge X X X X X X
1
Inside notes are entered electronically for automated moving boat and accoustic Doppler current profiler (ADCP).
2
Inside notes not required.
3
These items may not require direct entry. They should correspond to the front sheet entries for the given measurement, and may be provided directly with the
electronic processing system.
Table 5. Items to be entered to the electronic processing system from the inside body of a discharge measurement—Continued
Discharge Measurement Method
Item
Number
Measurement Item
Standard Current Meter
Ice
Moving Boat (Manual Only)
1
Acoustic Doppler current profiler
1
Dye Dilution
2
Portable Weir orFflume
Indirect
2
Surface Velocity
Volumetric
Estimate
2
16 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
4.2.1.2 Numbering Discharge Measurements
Although separate input formats are used for the various
types of measurements, all measurements are numbered con-
secutively and are maintained in only one file of discharge mea-
surements. The numbering sequence should begin with 1 for the
first discharge measurement of record, and continue consecu-
tively throughout the period of record, with all discharge mea-
surements numbered in chronological order. Discharge mea-
surement numbers may contain alphabetic characters (for
example, 127A, 127B, and others) to allow insertion of a mea-
surement in an established sequence. Renumbering of discharge
measurements should be discouraged.
4.2.2 Gage Datum Leveling
Leveling for the purpose of establishing or checking the
datum of reference marks, benchmarks, staff gages, wire-
weight gages, and other gage features is performed occasionally
at most gaging stations. Guidelines for leveling procedures are
described by Kennedy (1990). The electronic processing
system should provide capability to accept leveling data and
should be able to produce an analysis and summary of the lev-
eling information. Items that may be entered from the leveling
field notes are listed in table 6.
Table 6. Items that may be entered to an electronic processing system from level notes
[Note—Items 4–9, 11–21, and 23–24 may require more than one entry. For example, more than one reference mark, such as RM2, RM 3, RM 4, and others may
be present.]
1
1.
1
2.
1
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
Station identification number
Date of leveling
Party—initials and last name of each person
Benchmark number (Benchmark, or Reference mark, that is used for the base should be separately identified)
Benchmark elevation, as found by levels
Reference mark number
Reference mark elevation, as found by levels
Reference point number
Reference point elevation, as found by levels
Electric tape reference point elevation, as found by levels
Inside gage reference point elevation, as found by levels
Inside gage reference point elevation, as read on gage
Outside gage reference point elevations, as found by levels
Outside gage reference point elevation, as read on gage
Wire-weight elevation (bottom of weight), as found by levels
Wire-weight elevation, as read on dial and corresponding to above item
Wire-weight check bar elevation, as found by levels
Wire-weight check bar elevation, as read on dial
Outside water surface elevation, as read on outside reference gage
Inside water surface elevation, as read on inside reference gage
Time of reading outside and inside gages, for two above items
Base (primary reference gage) correction, as found by levels
Highwater mark elevation
Crest-stage gage reference point elevation, (top of rod/stick, bottom pin, etc), as found by levels
Orifice elevation, by levels
Point of zero flow elevation, as found by levels
Remarks—written comments from level notes
1
Mandatory.
4. Entry of Data to the Electronic Processing System 17
4.2.3 Crest-Stage Gage Data
Crest-stage gages are special gages capable of recording
the highest level that a flood peak reaches. These gages may be
operated independently as a partial record site, or they may be
operated at a continuous record site for the purpose of verifying
the peak gage height. A special note sheet is used to record data
and information for crest-stage gages. The electronic process-
ing system should be able to accept these data. Items that can be
entered from crest-stage gage note sheets are listed in table 7.
4.2.4 Channel and Control Cross Sections
Data defining cross sections of the stream channel and/or
control are useful in rating curve analysis. Also, unsteady-flow
model methods of computing stream discharge must have
cross-section data at intervals along the stream reach for which
the model is defined. The electronic processing system should
allow input of items necessary for defining the cross-section
location and the descriptors for each cross section. In addition,
Manning roughness coefficients may be required and should be
variable, both horizontally and vertically. For some cross sec-
tions that are considered section controls, a weir coefficient (C)
should be an optional entry, which also may be variable with
stage. Transverse stationing for cross sections should begin on
the left bank of the stream and increase from left to right. If
survey data are entered with transverse stationing that increases
from right to left, the electronic processing system should pro-
vide an automatic conversion of the data to the left-to-right for-
mat. The electronic processing system also should accomodate
input of cross-section data that were collected and recorded
electronically. A listing of data that should be allowable entries
for cross sections is listed in table 8.
Table 7. Items that may be entered to an electronic processing system from crest-stage gage notes
[Items 4–9 may require multiple entries to accomodate more than one crest-stage gage or highwater mark.]
1
1.
1
2.
1
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Station identification number
Date of crest-stage gage inspection
Party—Initials and last name of each person
Crest-stage gage identification (for example, upstream gage, downstream gage, and others)
Elevation of crest-stage gage reference point (top of rod/stick or bottom pin), as given in station description
Distance measured from crest-stage gage reference point to high water mark on rod/stick
Highwater mark elevation, as calculated from two above items
Highwater mark elevation, as determined from marks outside the crest-stage gage
Estimated date of highwater mark
Gage height of current water surface
Gage read to obtain corresponding item 10 above (staff gage, wire weight, tape down, or other)
Time of gage reading
Time zone
Remarks—written comments from notes
1
Mandatory.
Table 8. Items that may be entered to an electronic processing system from cross-section notes
[Multiple cross sections may be entered. For items 7–14 multiple entries may be entered]
1
1.
1
2.
1
3.
1
4.
1
5.
1
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Station identification number
Date of survey
Party—initials and last name of each person
Cross-section ID number—an alpha-numeric ID unique for each cross section.
A descriptive identification of the cross section, such as "section control" or "typical channel control section".
Longitudinal stationing, in ft, that locates the section relative to the gage. Positive stationing increases in the downstream direction
and negative stationing increases in the upstream direction. The gage is station 0.
Transverse stationing along the cross section, with the initial point beginning on the left bank.
Ground elevation for each transverse station.
Sub-area breakpoint station (rightmost transverse station of a sub-area).
Sub-area low elevation breakpoint for roughness coefficients.
Sub-area high elevation breakpoint for roughness coefficients.
Sub-area low elevation roughness coefficient, Manning’s n.
Sub-area high elevation roughness coefficient, Manning’s n.
Cross-section weir coefficient, C, if applicable (can be variable with stage).
Remarks
1
Mandatory.
18 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
4.2.5 Miscellaneous Field Notes
Miscellaneous field notes occasionally are made at most
gage sites. These may be just a gage reading, a measurement of
some feature or variable, or simply some written comments.
The electronic processing system should allow entry of these
notes. Items that might be entered from miscellaneous field
notes are listed in table 9.
5. Verification and Editing of Unit Values
Unit values for the various parameters, such as gage height
and velocity, must be carefully checked and verified before
used in further analysis. Erroneous or suspicious data may
require editing and appending special identification codes
(flags) to individual values. Before any editing is performed, the
original unit values should be set aside for archiving. Details of
archiving requirements are described in another part of this
report. This section of the report describes techniques for veri-
fication and editing, which includes time corrections, unit value
corrections, datum adjustments, various comparisons and cross-
checking, and flagging requirements. All verification, editing,
and time corrections must be performed on a copy of the origi-
nal data, and not on the original. This copy will become the
work file, and also will be archived following completion and
finalization of the records.
5.1 Times and Dates
Unit values of gage height and other streamflow parame-
ters generally are recorded in field instruments at a fixed time
interval, such as every 15 minutes, 1 hour, and so forth. The
time and date associated with each unit value are not always
recorded, but are determined on the basis of the initial time and
date, and the recording time interval. Times and dates are
recorded for each unit value when field recorders are pro-
grammed for variable time-interval data. Field instrument
clocks are fairly reliable, but occasionally clock errors will
result. True times and dates are those noted by the hydrographer
using his watch and calendar at the time the field instrument is
serviced. Servicing would be at the beginning and end of a
record period, and occasionally at intermediate points of a
record period. Also, the hydrographer should note the time-
system designation, such as CST, CDST, PST, and others,
whenever the time and date are noted. Times, dates, and time
system designations noted by hydrographers will be used as the
basis for making time corrections, standard and daylight sav-
ings time adjustments, and conversion to UTC of the unit value
data.
Data acquired by satellite DCP installations will have UTC
times and dates assigned automatically. These times and dates
are considered accurate and do not need adjustment or correc-
tion.
5.2 Time Corrections and Adjustments
Time corrections to account for clock errors may be neces-
sary for unit value data recorded in the field. In addition, all unit
value times must be adjusted to UTC time for purposes of
archiving. These time corrections and adjustments do not apply
to data collected by way of a satellite DCP because those data
are considered correct as collected.
5.2.1 Clock Error Corrections
The simplest case of clock error is where the beginning
time and date are correct and the ending time and date are incor-
rect by a known amount. Lacking any evidence of intermediate
clock or recorder problems, it usually is assumed that the clock
error is a gradual and uniform error. The correction for this type
of error should be prorated uniformly throughout the record
period.
A somewhat more complex case involves a clock or
recorder malfunction somewhere in the middle of the record
period, or where the clock was set wrong at the beginning of a
Table 9. Items that may be entered to an electronic processing system from miscellaneous field notes
[Items 4–6 and 8 may have multiple entries.]
1
1.
1
2.
1
3.
4.
5.
6.
7.
8.
9.
10.
Station identification number
Date of field notes
Party—initials and last name of each person
Gage reading of water surface
Gage read to obtain corresponding item 4 above (IG, OG, Tape, WW, recorder dial, other)
Time of gage reading
Time zone
Highwater mark elevation
Gage height of zero flow as determined from field measurement
Remarks—written comments from notes
1
Mandatory.
5. Verification and Editing of Unit Values 19
record period. One or more instances of intermediate clock
problems may result in some cases. The time-correction proce-
dure should allow the user to assign time and date values at
more than one place within a record period, and the electronic
processing system should adjust all intermediate or intervening
unit value times accordingly. Occasionally, it may not be possi-
ble to determine why the time for a record is incorrect, or at
what point in a record that timing problems occurred. A user
may need to make arbitrary time assignments, based on their
best judgement.
In some cases, intermediate time and date readings may be
available from discharge measurement notes or miscellaneous
field notes when the gage was visited but the record was not
removed. The electronic processing system should automati-
cally retrieve dates and times from the field note entries for
checking clock performance. This requires that the unit value
file has been marked or tagged in some way so the user can
identify the place in the record where the correct times and dates
apply. Such readings would be treated the same as described
above, and corrections would be made by linear proration
between adjacent readings.
Past methods for making time corrections, such as used in
ADAPS, provide a method referred to as the "historical"
method, whereby occasional unit values are dropped, or added,
in order to account for a time error. This method is not consid-
ered as good as the linear proration method and should not be
used.
The standard time-correction method, or linear proration
method, described herein will result in unit values of gage
height (or velocity, or other parameter) that will not be on the
even hour, or 15 minutes, or other even time. This is not consid-
ered detrimental to the record. If unit values of gage height (or
other parameter) are needed on the even hour or other even time
interval, they can be obtained by interpolation between the
time-adjusted values.
Time differences caused by a change into or out of daylight
savings time should not be treated the same as a clock error. If
a clock error exists during a period of record where the time
changed because of daylight savings time, the clock error
should first be prorated by assuming a uniform time designation
for all of the period of record being processed. The electronic
processing system should adjust times and dates input from
field notes to the same time designation. The clock error is then
corrected according to the user's instructions. After clock error
corrections are made, the record is automatically converted with
the electronic processing system to UTC time for storage and
archiving. No unit values would be dropped or artificially added
because of the daylight savings time change.
5.2.2 Universal Coordinated Time (UTC) Adjustments
All data and information should be stored and archived
with Universal Coordinated Time (UTC). Therefore, following
the standard time-correction method for making clock error
adjustments, the electronic processing system should automati-
cally adjust all local times to UTC. This is a simple process of
adding the time offset shown in table 3 to the recorded local
times. The recorded local times must have a time-zone designa-
tion as part of the input to define the time-zone system used for
recording.
Unit values used in other analyses, such as computation of
daily values, will adjust the UTC times to whatever time system
is designated by the user. In this way, the electronic processing
system can produce records on the basis of any designated time
system. The time adjustments resulting for a period where time
changes from standard time to daylight savings time, and for a
period where time changes from daylight savings time to stan-
dard time is illustrated in figure 1. Also shown are unit values
that would be used for computing daily values for days that
change between standard time and daylight savings time. Note
that all unit values are used in the computations, and none are
dropped or artifically added. The day when time changes into
daylight savings time will contain 23 hours, and the day when
time changes out of daylight savings time will contain 25 hours.
5.3 Parameter Value Verifications
Unit values of gage height and other parameters that have
been automatically measured and recorded by field instruments
always should be carefully inspected and verified before
accepting them for further analysis and computations. Various
methods are available in electronic data processing to make this
task relatively easy. The most frequently used methods are
threshold comparisons, rating comparisons, direct reading com-
parisons, and graphical methods. Of these, graphical methods
are the most versatile and can be easily adapted to any of the
other methods.
5.3.1 Threshold Comparisons
A threshold is a minimum or maximum value that can help
detect unit values that might be erroneous. Thresholds can be
compared directly to unit values, or to differences between
adjacent unit values. Testing a period of record against a set of
thresholds is performed automatically with the electronic pro-
cessing system. The user is alerted whenever a unit value
exceeds the threshold value. Thresholds can be established by
the user, or they can be automatically computed based on a
period of record.
The set of thresholds should consist of (1) a high-value
threshold, (2) a low-value threshold, (3) a maximum difference
threshold, and (4) a flat-spot threshold (maximum time for con-
stant values). Thresholds should be used to detect values that
are unusual and outside the normal expected range of the data.
For instance, an ADR punch recorder malfunctions and punches
additional holes in the paper tape, which translates to unit
values outside of the expected range of values. The threshold
check should alert the user to this condition. Maximum and
minimum threshold values should be set at or near the maxi-
mum and minimum values actually experienced during the past
20 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
3 to 5 years of record. The difference threshold also should be
set at or near the largest valid difference during the past 3 to 5
years.
Selection of threshold values should be based, if possible,
on an analysis of the observed record for the past 3 to 5 years.
This analysis should be performed with the electronic process-
ing system and should furnish listings of the 20 highest peak
unit values, and the 20 lowest trough unit values during the
period. The electronic processing system also should provide
the 20 greatest differences between consecutive unit values, and
the 20 longest time periods during which there was no change
in unit values (flat spots). This type of analysis would provide
data for the user to use in selecting appropriate thresholds and
would be performed every three years, or whenever it is desired
to change thresholds.
Threshold checking, if used primarily for the purpose of
identifying unit values that are outside the range of most expe-
rience, is a very valuable tool for identifying erroneous unit val-
ues. However, caution should be exercised if high-value thresh-
olds are set too low, or low-value thresholds set too high, so that
many unit values within the range of experience are identified
by the threshold test. In this case, the user always should apply
other methods to verify, or disqualify, unit values that have
failed the threshold test.
5.3.2 Rating Comparisons
A simple comparison, similar to threshold comparisons, is
the rating comparison. This comparison identifies all unit
values that exceed the high end or fall below the low end of the
rating currently in use. This comparison can be performed auto-
matically with the electronic processing system, because ratings
are stored in the electronic processing system. This test would
Unit
Value
Local
Date
Local
Time
UTC
Time
Time
Zone
Unit
Value
Local
Date
Local
Time
UTC
Time
Time
Zone
xxxx 04/03 2300 0400
EST xxxx 10/24 2300 0300 EDST
xxxx 04/03 2400 0500
xxxx 10/24 2400 0400
xxxx 04/04 0100 0600 xxxx 10/25 0100 0500 EDST
xxxx 0200 0700
EST xxxx 0100 0600 EST
xxxx 0400 0800
EDST xxxx 0200 0700
xxxx 0500 0900 xxxx 0300 0800
xxxx 0600 1000 xxxx 0400 0900
xxxx 0700 1100 xxxx 0500 1000
xxxx 0800 1200 xxxx 0600 1100
xxxx 0900 1300 xxxx 0700 1200
xxxx 1000 1400 xxxx 0800 1300
xxxx 1100 1500 xxxx 0900 1400
xxxx 1200 1600 xxxx 1000 1500
xxxx 1300 1700 xxxx 1100 1600
xxxx 1400 1800 xxxx 1200 1700
xxxx 1500 1900 xxxx 1300 1800
xxxx 1600 2000 xxxx 1400 1900
xxxx 1700 2100 xxxx 1500 2000
xxxx 1800 2200 xxxx 1600 2100
xxxx 1900 2300 xxxx 1700 2200
xxxx 2000 2400 xxxx 1800 2300
xxxx 2100 0100 xxxx 1900 2400
xxxx 2200 0200 xxxx 2000 0100
xxxx 2300 0300 xxxx 2100 0200
xxxx 04/04 2400 0400 xxxx 2200 0300
xxxx 04/05 0100 0500 xxxx 2300 0400
xxxx 0200 0600 xxxx 10/25 2400 0500
xxxx 0300 0700 xxxx 10/26 0100 0600
xxxx 04/05 0400 0800 EDST xxxx 10/26 0200 0700 EST
Example A—Time changes from standard time to daylight
savings time.
Example B—Time changes from daylight savings time to
standard time.
24 unit values used to compute daily value for April 4 26 unit values used to compute daily value for October 25
Figure 1. Comparison of time system examples where daylight savings time is used. [UTC, Coordinated Universal Time;
EST, Eastern Standard Time; EDST, Eastern Standard Daylight Savings Time.]
5. Verification and Editing of Unit Values 21
alert the user to possible erroneous unit values as well as to the
possible need to extend the rating currently in use.
5.3.3 Direct Reading Comparisons
Various types of direct readings may be available for com-
parison and verification of recorded unit values. These include
actual gage readings made by an observer or hydrographer,
readings obtained from maximum and minimum indicators,
highwater mark readings, and crest gage readings. All of these
various direct readings should be input to the electronic pro-
cessing system and automatically displayed to the user in con-
junction with the unit values being verified.
At some gaging stations auxiliary and/or backup gages are
operated in conjunction with the primary gage. In many cases,
the records from these gages can be used as an independent
check, or comparison, to the primary record.
5.3.4 Graphical Comparisons
Graphics can be the most important and easily used
method to verify a period of unit values. All of the methods
described in sections 5.3.1 through 5.3.3 should be incorporated
into a graphic system to automatically scan and review a period
of record for the purpose of verification. The primary record of
unit values should be plotted as a time series, with a unit-values
scale that allows the user to see each value clearly and that does
not distort the general shape of the record. The time scale should
automatically default to the time zone normally used for the sta-
tion, but there should be provision for the user to change to any
other time zone. A basic plot of unit values can be used to iden-
tify erroneous data by an experienced user. With the addition to
the plot of thresholds, rating limits, observer and hydrographer
gage readings, high water marks, maximum and minimum indi-
cator readings, and auxiliary gage records, much more can be
done to verify the primary record.
The primary record of recorded unit values should be plot-
ted and considered the base plot. The processing system should
plot all direct gage readings by observers and streamgagers at
the correct time on the base plot. High and low thresholds, high
and low rating limits, highwater mark readings, maximum and
minimum indicator readings, and crest-stage gage readings
should be plotted at their respective elevations as a horizontal
line that extends throughout the period of record being verified.
This process will allow the user to compare these readings to
peaks and troughs in the primary record. Auxiliary and backup
records should be plotted as a time series for comparison to the
primary record. The plotting system should use different colors
and symbols to easily distinguish the various components. Unit
values that trigger the difference threshold and the flat spot
threshold also should be easily identified by color or symbol.
5.4 Parameter Value Corrections
The verification process described in section 5.3 will
sometimes identify unit values of gage height or other parame-
ters that are either erroneous or suspected of being erroneous.
By definition, an erroneous gage reading results when the
recording instrument does not record the true parameter value
(for example, stage, velocity, and other) occurring in the stream,
lake, or other water body. A base, or reference gage, usually is
used for determining the true parameter value.
An erroneous gage reading can result from either instru-
ment errors or datum errors, or both. Instrument errors are
those errors resulting from a malfunction, an incorrect setting,
an incorrect calibration, or other problem with the recording
instrument. An instrument error usually can be detected by
comparing a recorded parameter value with a corresponding
reference gage reading. Datum errors, on the other hand, are
those errors resulting from a change in the reference gage, and
apply only to gage heights or elevations. A datum error usually
can be detected only by running levels to the reference gage,
using a stable benchmark of known elevation as a reference.
Another distinction between datum errors and instrument
errors, is that datum errors generally occur over a long period of
time (many months or years), whereas instrument errors usually
are short term (a few days or weeks). Consequently, corrections
for datum errors and instrument errors usually are made sepa-
rately. However, correction for datum errors should use the
same methods as those used for instrument errors, as described
in section 5.4.2 below for instrument error corrections.
When a parameter value, or series of values, has been
determined to be erroneous, it may be corrected, or edited, if the
user has a sufficient basis for doing so. Editing of individual
unit values should be allowed with the electronic processing
system at any of the verification steps, including the graphical
display. In the graphical display, the user should be allowed to
edit unit values directly on the graph, or in a supplemental table
of unit values. In addition to correcting and editing unit values,
the electronic processing system also should allow the user to
flag unit values in such a way that they will not be used in fur-
ther analysis.
5.4.1 Datum Adjustments and Conversions
The gage datum of a gage site usually is an arbitrary
datum, unique and specifically selected as a convenient work-
ing reference for each gage site. The datum frequently is located
at a level just below the lowest expected gage height, or just
below the gage height of zero flow. For some stations, such as
at reservoirs and coastal streams, the gage datum may not be
arbitrary, but is established to be the same as sea level, or other
known and common datum. In any case, there are times when
datum adjustments must be made to correct a datum error. Also,
there are some stations for which it is necessary to convert an
arbitrary datum to a known datum, such as sea level. These are
described in sections 5.4.1.1 and 5.4.1.2.
22 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
5.4.1.1 Adjustments For Gage Datum Error
Gage datum adjustments generally are considered to be
corrections applied to recorded gage heights and water-surface
elevations to make them consistent with the gage datum. Phys-
ical movement of a gage or gage structure can sometimes occur,
thereby causing an error of gage readings in relation to the gage
datum. Such a change may be gradual over a long period of
time, such as from settling or subsidence, or the change may be
sudden, such as from an earthquake, flood damage, or accident.
Whether the change is gradual or sudden, the result is the same,
in that the gage no longer records gage heights and elevations
that are correct in relation to the original gage datum. Gage
movement, relative to gage datum, is quantitatively measured
by leveling from stable reference marks or benchmarks of
known elevation. Leveling procedures for surface-water gaging
stations are well established and are described by Kennedy
(1990).
Datum errors should be carefully analyzed to determine
the best method to make corrections. Frequently, it cannot be
determined when a datum error occurred, and the best method
of correction is to prorate it uniformly throughout the period in
question. If a specific time of occurrence can be defined, then
the correction can be made starting at that time and carrying the
correction forward until the datum is restored. As a general rule,
corrections for gage-datum errors of 0.02 ft or less are not
applied, except in cases where smaller gage-datum errors are
critical in correctly defining another parameter, such as for res-
ervoir contents computations. Small errors of this kind usually
are absorbed by ratings and rating shifts.
5.4.1.2 Conversion to NGVD or Other Datum
In addition to making datum adjustments for the purpose
of correcting gage-height values that are incorrect because of a
change of the base (reference) gage, it is sometimes necessary
to convert recorded gage heights to a different datum. The most
common conversion is where the recorded values must be con-
verted to National Geodetic Vertical Datum (NGVD), some-
times referred to as mean sea level. This type of conversion
requires that a constant value be added to, or subtracted from,
the recorded gage heights throughout the record period. A gage
datum adjustment for gage movement, as described in section
5.4.1.1, also may be needed at times. In such cases, two simul-
taneous adjustments would be needed.
5.4.2 Instrument Error Corrections
Recording instruments and parameter sensors may, at
times, produce erroneous gage readings for a number of rea-
sons. For example, float tapes may slip, recorders may punch
incorrectly, gage drawdown because of high velocity may occur
at some stages, stage or velocity sensors may drift because of
temperature or other reason, and the recorder even may be set
wrong by the user. These, and numerous other causes, will
result in erroneous unit values of gage height, velocity, or other
parameters.
The electronic processing system must provide easy and
quick ways to make corrections when instrument errors are
identified. Corrections should be possible through a graphical
interface, such as the one described above for review and veri-
fication, and also with a tabular format. The user should be able
to make corrections to individual unit values, or to sequences of
unit values. Three types of corrections should be available for
use; (1) constant value corrections, (2) parameter (usually
stage) variable corrections, and (3) time variable corrections.
To make entry and application of the corrections as easy as pos-
sible, each of these types of corrections should be definable on
the same entry form or graphical interface. In addition, the same
methods and entry form should be applicable to datum error
corrections.
5.4.2.1 Constant Value Corrections
Constant value corrections are simply the addition or sub-
traction of a constant value from a sequence of unit values. The
user should be able to specify the constant value correction to
be used, and the dates and times for which the correction is to
be applied. The electronic processing system then should apply
the correction automatically.
5.4.2.2 Parameter Variable Corrections
Certain types of parameter errors may vary according to
the value of the parameter. For instance, for some gaging sta-
tions the stage measurements may not reflect actual river stage
because of drawdown caused by high flow velocity near the
gage intake or orifice. The resulting stage error is directly
related to the velocity, which in turn is often related to the stage.
A relation between stage and stage-correction can sometimes be
defined that is reasonably consistent for long time periods and
can be used to determine the gage-height correction on the basis
of the recorded stage.
Parameter variable corrections require a relation between
the parameter and the correction. The user should be able to
input this relation to the electronic processing system, along
with a starting date and time, and if needed an ending date and
time. The electronic processing system should calculate and
apply the corrections automatically. When a correction relation
of this type is entered, and no ending date and time are speci-
fied, then it should be continued in use until such time that an
ending date and time are specified.
A parameter variable correction relation should be defined
by entering point pairs of parameter and corresponding correc-
tions for as many points as necessary through the intended range
of correction. The processing system should automatically
interpolate corrections that are needed between the input points.
If parameter values occur below the lowest point of the correc-
tion relation, then the correction value for the lowest point of the
relation should be used for all corrections below this point.
Likewise, the correction values above the highest point of the
correction relation should be the same as the highest correction
5. Verification and Editing of Unit Values 23
value of the relation. Alternatively, the correction relation can
be entered as an equation. Upper and lower limits of the input
parameter should be specified for the equation. The correction
values corresponding to these limits should be held constant
when parameter values are less than the lower limit or greater
than the upper limit.
5.4.2.3 Time Variable Corrections
Time variable corrections are corrections that are distrib-
uted between specified dates and times. This type of correction
usually is referred to as time proration. Time proration should
apply to singular correction values and to parameter variable
correction relations. Likewise, time variable corrections should
apply to datum corrections as well as instrument error correc-
tions.
Corrections that do not vary with parameter value are con-
sidered a singular correction for a given point in time. However,
such a correction may vary with time. For example, at the
beginning of a time series of unit values, a correction of +0.15
ft is defined, which does not vary with stage. At a subsequent
date and time, a correction of +0.10 ft is defined, which likewise
does not vary with stage. The electronic processing system
should allow the user to make a linear, time proration between
these two correction values and defined times.
Corrections that vary with parameter value (as defined by
a parameter variable correction relation) sometimes gradually
may change shape or position with time. The electronic pro-
cessing system should allow time proration between two con-
secutive parameter variable correction relations. Time proration
between two correction relations should be made on the basis of
equal parameter values. For example, assume that a correction
relation is entered with a date and time. A second correction
relation is entered with a subsequent date and time. At some
intermediate date and time, assume that the gage height is 4.23
ft. Correction values are determined from each of the two cor-
rection relations for a gage height of 4.23 ft, resulting in two
correction values, one at the start of the proration period, and
one at the end of the proration period. The correction that
applies to the intermediate date and time, for the gage height of
4.23 ft., is determined by time interpolation between the two
correction values.
5.4.3 Numbering Correction Relations
Parameter variable correction relations should be num-
bered for ease of identification, reuse, and archiving. A simple
consecutive number sequence for each year is preferred, such as
1997.1, 1997.2, 1997.3, and so forth.
5.4.4 Additive Corrections
Sometimes, more than one correction for the same period
of unit values may be needed. For instance, a datum correction
may be needed during the same period of time that a parameter
variable correction relation is needed. If both corrections are
defined, and the dates and times overlap, the electronic process-
ing system automatically should apply both corrections simul-
taneously for the overlapping period. In other words, all correc-
tions that are defined for the same date and time, or for the same
type of correction, become additive. There should be no limit as
to the number of corrections that can be used for a given date
and time, but it is not likely that more than two or three would
be required.
5.4.5 Identification of Corrections
The electronic processing system should provide the
option to identify the separate corrections entered by the user. It
is recommended that a standard group of correction types be
defined as (1) instrument error, (2) datum error, (3) datum
adjustment, (4) velocity drawdown error, and (5) other. When a
correction is entered by the user, one of these types can be
selected to describe the correction. Each type should have pro-
vision to enter additional descriptive text, if necessary.
5.4.6 Flagging of unit values
Corrections cannot always be determined for unit values,
and in fact, corrections are not always desired for unit values.
For certain situations it is recommended that daily values be
estimated rather than attempting to correct, or estimate, unit val-
ues. In these situations, the user should be able to mark, or flag,
specific unit values to specify the reason they are not used. The
flags also will be an indicator in other parts of the electronic
processing system, such as the primary computations, to ignore
the unit values for certain kinds of computations. The following
flags are recommended.
•Affected—This flag is for unit values that are correct
and representative of the true stage (or other parame-
ter), but because of some irregular condition the rating
is severely affected and may not be applicable. This flag
should be used for severe conditions of backwater from
irregular downstream conditions, backwater from ice,
and other conditions. The flag should not be used for
normal shifting control conditions.
• Erroneous—This flag is for incorrect unit values. For
instance, the float is resting on mud in the stilling well,
and the recorded unit values do not represent the stage
in the stream.
•Missing—This flag is reserved for situations where unit
values were expected, but because of some malfunction
of equipment where no data were recorded.
• Estimated—This flag is used for estimated unit values.
It should be automatically attached to unit values that
are changed by the user.
The first three types of flags defined above are intended
primarily for the original, archivable, unit values. These flags
will document, for historical purposes, the evaluation and inter-
24 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
pretation of the validity of the recorded unit values. They also
should be carried forward for the analysis and computation of
records. In the analysis and computations, it may be desirable to
estimate unit values in certain situations. The fourth type of flag
is reserved for estimated values, which may replace affected,
erroneous, or missing data. The estimated flag only wll be used
for unit values in data sets generated subsequent to the original
data set. Unit values flagged as affected or erroneous should not
be used in the primary computations.
6. Verification and Analysis of Field
Measurement Data
Field measurement data and information that are entered
into the electronic processing system include discharge mea-
surements, gage datum leveling measurements, crest-stage gage
data, channel and control cross-section data, and miscellaneous
field notes. All of these data usually are entered by keyboard,
except that some discharge measurements are entered from
electronic field computers. Various computations and compari-
sons should be made to verify the accuracy and insure the con-
sistency of the information. Sections 6.1.1 through 6.1.3
describe some of the verification, computations, and cross
checking that should be performed with the electronic process-
ing system. Errors resulting from data entry and incorrect com-
putation should be corrected by the user.
It is important to emphasize that measurement data should
not be deleted or erased from the original notes, which in most
cases are the paper note sheets. Editing of data that are entered
from paper notes to the electronic processing system is permit-
ted, provided the data were entered by keyboard. This editing
allows for correction of keyboard entry errors without compro-
mising the integrity of the original paper notes. On the other
hand, data entered electronically, such as from an electronic
field computer, should not be edited, changed, or deleted
because once they are entered to the electronic processing
system they become the original copy which will be used for
archiving. It is assumed that no errors occur during an electronic
transfer. All information in measurement notes (for example,
computed values such as area, velocity, width, discharge, and
others) may be edited and changed regardless of the entry
method. Obviously, these values should be arithmetically cor-
rect and based on the original data.
6.1 Discharge Measurement Analysis
All discharge measurements should be checked wherever
possible for arithmetic errors, logic errors, and other inconsis-
tencies, with the electronic processing system. In addition, the
electronic processing system should compute the standard error
for regular current meter measurements. If a rating is available
for the gaging station, the electronic processing system should
compute the shift, or deviation, of the measurement from the
rating. The shift analysis would apply to stage-discharge, slope,
rate-of-change in stage and velocity-index ratings.
Most of the following checking and computation steps
apply only to standard current meter measurements. See section
6.1.5 for other types of measurements where checking proce-
dures differ.
6.1.1 Arithmetic Checking
A summary of the numerical results of a discharge mea-
surement is entered to the electronic processing system from
what usually is referred to as the front sheet of the measurement.
Most of these numbers are computed from the field measure-
ment data, that are part of the inside body of the measurement.
For discharge measurements recorded on paper forms, the com-
putations are made by the hydrographer in the field with a cal-
culator. If an electronic field notebook was used for recording
the discharge measurement data, then the computations were
made automatically by the field notebook, and little or no arith-
metic checking is required.
When original computations are made on paper forms, the
following checks of the inside part of the measurement should
be made with the electronic processing system:
• Subsection width—The width for a subsection is com-
puted as one-half the distance between the preceeding
vertical stationing and the succeeding vertical station-
ing. For verticals at the edge of a channel or bridge pier,
the subsection width is computed as one-half the dis-
tance to the adjacent vertical.
• Point velocities—If a current meter rating or equation
has been entered for the current meter used in making
the discharge measurement, then each point velocity
should be checked.
•Mean velocity for each vertical—The mean velocity
for each vertical is computed as follows:
For the one-point method, the mean velocity is equal to
the point velocity at the 0.6 depth. If the point velocity
was measured at a depth other than the 0.6 depth, then
the mean velocity for the vertical is computed by mul-
tiplying the point velocity by the method coefficient. If
a method coefficient has not been entered for the verti-
cal, then the electronic processing system should warn
the hydrogapher and provide an opportunity to enter a
method coefficient. The user can choose to ignore the
warning.
For the two-point method, the mean velocity is equal to
a mean of the point velocities for the 0.2 and 0.8
depths.
For the three-point method, the mean velocity is equal
to a weighted mean of the 0.2 depth velocity, the 0.6
depth velocity, and the 0.8 depth velocity, where the 0.6
depth velocity is given double weight.
6. Verification and Analysis of Field Measurement Data 25
• Subsection mean velocity—The mean velocity for each
subsection is computed as the product of the mean
velocity of the vertical and the horizontal angle coeffi-
cient. If a horizontal angle coefficient is not entered for
the vertical, then the electronic processing system
should assume a value of 1.00.
• Subsection area—The area for each subsection is com-
puted as the product of the subsection width and the
depth at the vertical.
• Subsection discharge—The discharge for each subsec-
tion is computed as the product of the subsection area
and the subsection mean velocity.
•Total width—The total width for each channel is com-
puted by summing the subsection widths.
•Total area—The total area for each channel is com-
puted by summing the subsection areas.
•Total discharge—The total discharge for each channel
is computed by summing the subsection discharges.
•Total number of verticals—The total number of verti-
cals for a measurement is simply a count of the number
of verticals, and includes the beginning and ending
points where depth often is equal to zero.
•Average velocity—The average velocity for each chan-
nel is computed by dividing the total discharge by the
total area.
•Totals for multiple channels—When the discharge
measurement has two or more channels, such as for a
braided stream, or a flood measurement that has a main
channel and one or more overflow channels, the grand
total of width, area, discharge, and number of verticals
is computed. These grand totals are the values used to
summarize the discharge measurement on the front
sheet. The average velocity for the measurement is the
grand total of discharge divided by the grand total of
area.
6.1.2 Logic and Consistency Checking
Information entered to the electronic processing system
from one part of the discharge measurement notes should be
automatically compared and cross checked with information
from other parts of the measurement to verify that it is logical
and consistent. The electronic processing system should alert
the user when inconsistencies occur and provide an opportunity
to make a change. In addition, when specific information items
are entered, the electronic processing system then should limit
the entry of other items so that the choices are consistent among
themselves. For instance, if the type of measurement is entered
as a wading measurement, then the choices for equipment entry
would be limited to the various types of wading rods. A listing
of some of the possible logic and consistency checks are given
below:
• Compare measurement sequence number with mea-
surement date and time—Measurement numbers gen-
erally are in sequential order according to date and
time.
• Compare measurement mean gage height(s) to gage
readings—The mean gage height should be a value that
falls between the lowest and highest gage readings
recorded during the course of making the discharge
measurement.
• Compare gage-height change to gage readings—The
gage-height change should be the difference between
the gage heights at the start and end of the discharge
measurement.
• Compare gage-height change time to start and end
time—The gage-height change time should be the dif-
ference between the start and end time of the discharge
measurement.
• Compare stream width on summary input to stream
width for inside note input—The stream width on the
summary input should be exactly the same as the
stream width computed and entered for the inside note
input. For multiple channels the stream width should be
the sum of individual channel widths.
• Compare stream area on summary input to stream area
for inside note input—The stream area on the summary
input should be exactly the same as the area computed
and entered for the inside note input. For multiple chan-
nels the stream area should be the sum of the individual
channel areas.
• Check mean velocity—The mean velocity should be
checked by dividing the measured discharge by the
stream area.
• Compare number of sections on summary input to
number of section for inside note input—The number
of sections should be the total number of verticals used
for making the discharge measurement. This total
includes each end section of the measurement, even
though depth and velocity at these points may be zero.
For multiple channels, the number of sections should be
the sum of the sections for individual channels.
• Check adjusted discharge—If an adjusted discharge is
entered, the electronic processing system should com-
pute an adjusted discharge based on the adjustment
method, if stated. This computed value should be com-
pared to the entered value.
• Check average time of point velocities—The average
time of point velocities on the summary input should
agree with the average of the time of current-meter rev-
olutions entered for the inside note input.
• Compare gage height of zero flow to gage read-
ings—The gage height of zero flow should be less than
the mean gage height of the discharge measurement,
26 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
and less than the gage heights in the gage-height table,
except in the cases of a zero flow measurement.
6.1.3 Computation of Measurement Error
The standard error of regular open-water, current-meter
discharge measurements can be computed based on the method
described by Sauer and Meyer (1992). Specific information
needed to make this computation includes current-meter type
(Price AA or Pygmy), current-meter rating type (standard or
individual), streambed conditions, suspension method, average
observation time of individual velocities, average channel
depth, average velocity, number of verticals, horizontal angle
information, and velocity measurement method (one-point,
two-point, and so forth). Much of this information is part of the
regular entry of discharge measurement data. The discharge
measurement entry form should allow for the entry of any miss-
ing items of information, and when all requirements are met the
electronic processing system should automatically compute the
measurement standard error and display it on the measurement
entry form.
The standard error computation described above only can
be used for regular open-water, current-meter discharge mea-
surements, according to the limitations described by Sauer and
Meyer (1992). It should not be used for ice measurements,
moving boat measurements, and acoustic velocity measure-
ments, indirect measurements, portable flume measurements,
dye dilution measurements, volumetric measurements, and dis-
charge estimates.
6.1.4 Shift Analysis
Discharge measurements are used primarily to check
rating curves to insure that currently used rating curves still are
applicable and have not changed. The electronic processing
system should automatically compute the shift information for
each discharge measurement The shift information should, by
default, be computed on the basis of the rating curve applicable
for the time and date of the discharge measurement; however,
the user should be allowed to specify a different rating curve for
which the shift information is computed. If, at a later date, a new
rating curve is prepared, then the shift information should be
automatically updated for all measurements that fall within the
period of time that the new rating is applicable. Shift informa-
tion, as noted in sections 6.1.4.1 through 6.1.4.4, should be dis-
played as part of the output for each discharge measurement.
Sections 6.1.4.1 through 6.1.4.4, respectively, describe the
methods of computing shift information for discharge measure-
ments made at stage-discharge stations, slope stations, rate-of-
change in stage stations, and velocity-index stations. Shifts are
not computed or used for structure stations and BRANCH
model stations. Definition of shift curves, use of partial or aver-
age shifts, and other aspects of shift application are described in
section 8.
All shift information should be computed on the basis of
standard rounding for discharge measurements, which usually
is three significant figures for discharge and hundredths of a
foot for gage height. Percent differences should be rounded to
tenths of a percent.
6.1.4.1 Shifts for Stage-Discharge Ratings
The shift information that should be computed for dis-
charge measurements applicable to stage-discharge rating
curves is as follows:
• Rating shift, S
r
—This shift is the numerical difference
between the gage height, G
r
, that corresponds with the
rating curve discharge for the measurement, and the
gage height, G
m
, of the discharge measurement. The
resulting algebraic sign should be observed. The equa-
tion is
(1)
• Measurement percent difference, D
%
—This is the per-
cent difference between the measured discharge, Q
m
,
and the rating curve discharge, Q
r
, that corresponds to
the gage height of the discharge measurement. This
represents the difference between the measured dis-
charge and rating discharge if no shift is applied. The
equation is
D
%
= 100 (Q
m
– Q
r
)/Q
r
(2)
• Shifts for the gage height of zero flow, S
0
—If the gage
height of zero flow, G
0
, is determined either when a reg-
ular discharge measurement is made, or independently
during a visit to the gaging station, then it is possible to
compute a shift for that gage height if the rating curve
is defined down to zero flow. This information can be
very useful as an aid in defining the low end of a shift
curve. The equation for computing the shift for the gage
height of zero flow is similar to equation 1 for comput-
ing the rating shift, and is
(3)
Because the discharge corresponding to G
0
is by definition
zero, it is not possible to compute a measurement percent differ-
ence.
6.1.4.2 Shifts for Slope Ratings
Slope ratings usually are referred to as complex ratings
because they involve two sites for measuring gage height (a
base gage and an auxiliary gage) and three individual ratings of
different parameters. The required ratings are (1) a stage-dis-
charge rating, (2) a stage-fall rating, and (3) a fall ratio-dis-
charge ratio rating. The use of these ratings for computing dis-
charge are described in section 9.1.4. The purpose of this
section is to describe how shift information is computed for
S
r
G
r
G
m
–=
S
0
G
r
G
0
–=
6. Verification and Analysis of Field Measurement Data 27
individual discharge measurements at stations with slope rat-
ings.
The stage-discharge rating is the only rating of the three
slope station ratings that is allowed to be shifted, and shift infor-
mation is referenced to this rating. If either the fall rating or the
ratio rating change, then new ratings should be prepared. It also
should be noted that slope ratings only may apply to certain
ranges of stage, and in some cases only when the fall is less than
a specified amount.
For slope ratings, the measured discharge, Q
m
, is consid-
ered the true discharge. The adjusted discharge, Q
adj
, is an
adjustment of the measured discharge that is computed by using
the observed stages at the base gage and the auxiliary gage, the
observed fall, which is the difference between the two observed
stages, and the defined rating curves. This adjusted discharge is
used for comparison to the rating discharge, Q
r
, to determine
shift information. If no shift is present, then Q
adj
and Q
r
will be
equal. The method for computing Q
adj
and shift information is
given in the following paragraphs.
• Adjusted discharge, Q
adj
—Compute the measured fall,
F
m
, as the difference between the observed mean gage
height for the measurement at the base gage, G
b
, and
the auxiliary gage, G
a
. The equation is
(4)
1. If the auxiliary gage is upstream from the base gage,
reverse the order of G
b
and G
a
in equation 4.
2. Determine the rating fall, F
r
, that corresponds to the base
gage height, G
b
, from the stage-fall rating.
3. Compute the fall ratio, R
f
, of the measured fall to the
rating fall. The equation is
(5)
4. Determine the discharge ratio, R
q
, corresponding to R
f
from the ratio rating.
5. Compute the adjusted discharge, Q
adj
, based on the
measured discharge, Q
m
, and the discharge ratio, R
q
, is
(6)
• Stage-discharge rating shift, S
r
—Determine the gage
height, G
r
, corresponding to the adjusted discharge,
Q
adj
, from the stage-discharge rating.
Compute the shift, S
r
, based on the observed gage
height, G
b
, for the base gage and the rating gage height,
G
r
. The equation is
(7)
• Measurement percent difference, D
%
—The percent
difference, D
%
, between the adjusted discharge, Q
adj
,
and the rating discharge, Q
r
, also should be computed.
This percentage represents the error of the adjusted dis-
charge from the rating discharge if no shift is applied.
The equation is
D
%
=100(Q
adj
-Q
r
)/Q
r
(8)
6.1.4.3 Shifts For Rate-of-Change In Stage Ratings
Rate-of-change in stage ratings are complex ratings that
include a stage-discharge rating, and a rating of stage and the
factor, 1/US
c
. This type of rating is referred to as the Boyer
method (see Rantz and others, 1982), and applies for streams
where rapid changes in stage affect the stage-discharge rating.
The term 1/US
c
is a measure of flood-wave velocity, U, and the
constant discharge stream slope, S
c
. This term usually is
defined empirically from the discharge measurements. The
greatest effect of changing stage occurs on streams having rela-
tively mild slopes, and rapid changes in discharges. Frequently,
this effect will happen when the flow regime of a stream has
been changed artificially, such as below a dam when releases
are made quickly, or in urban areas where basin development
causes rapid increases in flow rates for a stream that was previ-
ously sluggish.
Shift information for Boyer ratings should be computed
only for the stage-discharge rating. The rating of stage-1/US
c
should not be shifted. If this rating changes, then a new rating
should be prepared. The shift and percent difference should be
based on the rating discharge, Q
r
, and the adjusted discharge,
Q
adj
.
The method for computing the adjusted discharge and the
shift information for Boyer ratings is as follows.
• Adjusted discharge, Q
adj
—Compute the change in
stage, dG, for the discharge measurement as the differ-
ence between the ending gage height, G
e
, and the start-
ing gage height, G
s
. For rising stages the difference is
positive, and for falling stages the difference is nega-
tive. The equation is
(9)
1. Compute the elapsed time, dt, for the discharge measure-
ment as the difference between the ending time, t
e
and the
starting time, t
s
. The equation is
(10)
2. Compute the rate-of-change in stage, dG/dt, for the
discharge measurement.
3. Determine the factor, 1/US
c
, for the mean gage height of
the discharge measurement, from the stage-1/US
c
rating.
4. Compute the adjustment factor, F
adj
, using
. (11)
5. Compute the adjusted discharge, Q
adj
, as
F
m
G
b
G
a
–=
R
f
F
m
F
r
⁄=
Q
adj
Q
m
R
q
⁄=
S
r
G
r
G
b
–=
dG G
e
G
s
–=
dt t
e
t
s
–=
F
adj
1
1
US
c
---------
〈〉
dG
dt
-------
〈〉+=
28 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
(12)
6. The adjusted discharge, Q
adj
, represents the discharge that
would be computed from the two ratings and the observed
gage height if no shift is applied.
• Rating shift, S
r
—Determine the rating gage height, G
r
,
corresponding to the adjusted discharge, Q
adj
, from the
stage-discharge rating.
Compute the shift, S
r
, as the difference between the
rating gage height, G
r
, and the measured gage height,
G
m
, as
(13)
• Measurement percent difference, D
%
—Determine the
rating discharge, Q
r
, from the stage-discharge rating
using the measured mean gage height, G
m
.
Compute the percent difference, D
%
, between the
adjusted discharged, Q
adj
, and the rating discharge, Q
r
,
as
D
%
= 100(Q
adj
– Q
r
)/Q
r
(14)
This percent difference represents the error between the
Boyer adjusted discharge and the rating discharge if no shift
adjustment is applied.
6.1.4.4 Shifts for Velocity-Index Stations
Ratings at gaging stations with velocity index as part of the
rating system are considered complex ratings, and in some
cases can be extremely complex if two or more velocity meters
are in use. Stream channels may be subdivided either vertically
or horizontally, with each subdivision having a specific set of
ratings, or in some cases the individual meters may be averaged
for use with one set of ratings. Also, for some stations discharge
measurements may be made so that only the total discharge is
computed, with no accurate method of subdividing the mea-
sured discharge into the various rating components. Because of
this variability in the way velocity-index stations are processed,
it is not possible to describe all of the ways that rating shifts are
computed. The electronic processing system should provide an
interactive mode that allows the user to define the shifts and the
shifting method.
Shift information for a basic velocity-index rating is
described in the following paragraphs. A basic velocity-index
rating includes a single rating of stage and cross-section area, a
single rating of index velocity and mean velocity, and in some
cases an optional rating of stage and a velocity correction factor.
The rating discharge, Q
r
, is computed by multiplying the cross-
section area, A
r
, from the area rating, times the mean velocity,
V
r
, from the velocity rating, and times the velocity correction
factor, K
r
, from the stage-factor rating. If the velocity correc-
tion factor is not used, it is set to a default value of 1.00. The
basic velocity-index equation for discharge is
(15)
Shifts are allowed only for computation of V
r
from the
velocity rating. The stage-area and stage-factor ratings should
not be adjusted through the use of shifts. If either the stage-area
or the stage-factor ratings change, then new ratings should be
prepared.
It also should be noted that a standard cross section must
be used for the ratings and for computing shifts. That is, a spe-
cific cross section in the stream channel should be designated as
the rating section. This cross section may be the same section as
used for making discharge measurements or it may be a differ-
ent section. All computations should be related to and based on
the standard cross section. For instance, the mean stream veloc-
ity, as used for rating purposes, should be computed by dividing
the measured discharge by the cross-section area determined
from the stage-area rating of the standard cross section. This
mean stream velocity is the velocity that should be used to
check or define the velocity rating, and the one to be used for
plotting purposes on the velocity rating, for those sites where a
stage-factor rating is not used. If a stage-factor rating is used,
then this velocity should be adjusted by dividing it by the appli-
cable factor before using it to check or define the velocity rat-
ing.
The order of computations for shift determinations is
important because two, and in some cases three, ratings are
involved. The following step-by-step procedure should be used:
Standard cross-section area, A
r
—Determine the cross-
sectional area, A
r
, of the standard cross section from the stage-
area rating, using the mean gage height, G
m
, of the discharge
measurement.
Velocity correction factor, K
r
—Determine the velocity
correction factor, K
r
, from the rating of stage and velocity cor-
rection factor, using the mean gage height, G
m
, of the discharge
measurement. If this rating is not used, then set the velocity cor-
rection factor to a default value of 1.00.
Adjusted mean stream velocity, V
m
—Compute the mean
stream velocity, adjusted for the velocity correction factor, for
the standard cross section using
, (16)
where Q
m
is the measured discharge, and the other vari-
ables are as previously defined.
Rating index velocity, V
ir
—Determine the rating index
velocity from the rating of index velocity and mean stream
velocity, by entering the rating with the adjusted mean stream
velocity, V
m
, as computed in equation 16.
Index velocity shift, S
v
—Compute the index velocity shift
as the difference between the rating index velocity, V
ir
, and the
mean measured index velocity, V
im
, for the discharge measure-
ment. The shift, S
v
, is defined by
. (17)
Q
adj
Q
m
F
adj
⁄=
S
r
G
r
G
m
–=
Q
r
A
r
V
r
K
r
××=
V
m
Q
m
A
r
K
r
×
-----------------=
S
v
V
ir
V
im
–=
6. Verification and Analysis of Field Measurement Data 29
S
v
should retain the resulting algebraic sign (+ or -) for
application purposes. When the computed shift is applied to the
measured index velocity, V
im
, it will yield a corrected index
velocity to use for entry to the velocity rating when determining
the rating mean velocity, V
r
.
• Measurement percent difference, D
%
—The measure-
ment percent difference is the percentage of error
between the measured discharge, Q
m
, and the discharge
computed by using the ratings without shifts. To com-
pute this unshifted rating discharge, Q
r
, first determine
the standard cross-section rating area, A
r
, correspond-
ing to the observed stage of the discharge measurement.
Then determine the rating mean velocity, V
r
, corre-
sponding to the index velocity observed for the dis-
charge measurement. If a factor rating is used for the
site, determine the rating factor, K
r
, corresponding to
the observed stage of the discharge measurement. If a
factor rating is not used for the site, the rating factor
defaults to 1.00. Finally, compute the rating discharge,
Q
r
, using equation 15.
The measurement percent difference is computed as
D
%
= 100(Q
m
– Q
r
)/Q
r .
(18)
6.1.5 Special Procedures for Other Types of Discharge
Measurements
Some discharge measurements are made under conditions
that require computational procedures that are different than the
standard open-water, current-meter discharge measurement
described in preceding sections. In some cases, the differences
are minor, but in other cases the measurement method is com-
pletely different. Also, some measurement methods use highly
specialized equipment and recording methods that differ
entirely from those of standard discharge measurements. The
following sections describe some of the verification, editing,
and computations that should be performed with the electronic
processing system for each of the various types of measure-
ments.
6.1.5.1 Ice Measurements
Ice measurements, in most respects, are the same as a stan-
dard open-water discharge measurement. All of the same arith-
metic checking, logic and consistency checking, and shift anal-
ysis should be performed on ice measurements. Differences
between computations for a standard discharge measurement
and an ice measurement are listed below:
• Computation of effective depth—The inside body of
the discharge measurement notes for ice measurements
contains two additional columns of data and informa-
tion. One of the extra data columns is a field measure-
ment of the vertical distance between the free water
surface and the bottom of the ice (solid or slush ice).
These measurements should be compared to the total
depth for each vertical, and if in any given vertical the
depth from the water surface to the bottom of the ice is
found to be greater than the total depth, a warning mes-
sage should be issued by the electronic processing
system to the user.
The second additional column is effective depth, d
e
, for
each vertical and is computed as the difference between the total
depth, D, and the vertical distance, d
i
, between the free water
surface and the bottom of the ice. The equation is
(19)
• Computation of subsection area—The area of each
subsection is computed by multiplying the subsection
width times the effective depth, d
e
, of the vertical.
• Velocity coefficient—For verticals where the 0.6 depth
method is used to observe velocity, it is frequently nec-
essary to apply a velocity coefficient to correct for the
ice effect on the vertical velocity distribution. This
velocity coefficient is similar to the use of a method
coefficient for computing the mean velocity in a verti-
cal, as described in section 6.1.1 on arithmetic check-
ing. The mean velocity in the vertical is computed by
multiplying the velocity coefficient times the point
velocity observed at the 0.6 depth. If a velocity coeffi-
cient is not given, then it should default to 1.00. If the
two-point method (0.2 depth/0.8 depth) is used to
observe velocity, then no velocity coefficient is neces-
sary.
• Shift computations—Shifts are not usually computed
for ice measurements, but in some cases may be
desired. The user should have the option to specify if
shifts should be computed, and if so, they should be
computed just as they are for a regular open-water mea-
surement.
• Percent difference from rating curve—The difference,
in percent, between the measured discharge and the
rating curve should be computed for all ice measure-
ments, based on the same method as described in sec-
tion 6.1.4.1 for standard discharge measurements.
• Discharge ratio—For some gaging stations, the dis-
charge-ratio method is used for computing ice records.
The user should have the option to specify the compu-
tation of the ratio if it is used. The electronic processing
system then should compute the ratio, K
i
, for each ice
measurement as the ratio of the measured discharge,
Q
m
, to the open-water rating discharge, Q
r
, that corre-
sponds to the mean gage height of the measurement as
. (20)
d
e
Dd
i
–=
K
i
Q
m
Q
r
⁄=
30 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
6.1.5.2 Measurements With Vertical Angles
Depth measurements of deep, swift streams that are made
with cable suspension equipment from bridges, cableways, and
boats cannot always be made directly. Frequently, the sounding
weight is carried downstream by the current, and consequently
the observed depth is greater than the true vertical depth. In such
cases, corrections must be made to the observed depth in the
field at the time the measurement is made. The body of the field
notes for these measurements contain additional columns for
recording air-line vertical distance, observed depth, vertical
angle, and computed vertical depth. The corrections, which usu-
ally are not recorded in the field notes, account for an air-line
correction and a wet-line correction of the sounding cable. In
some cases, such as when sounding line tags are used, the air-
line correction may be eliminated or reduced to a negligible
amount.
The electronic processing system should contain the air-
line correction table and the wet-line table so that the computed
vertical depth can be checked. These tables are given by Rantz
and others (1982), which also provides a detailed description of
the computation methods. A brief summary of the procedure is
listed below.
1. Determine the air-line correction based on the observed air-
line vertical distance between the sounding equipment and
the water surface, the observed vertical angle, and the air-
line correction table.
2. Subtract the air-line correction (if used) from the
uncorrected observed depth of water. This subtraction
must be made before determining the wet-line correction.
3. Determine the wet-line correction based on the air-line
corrected observed depth, the observed vertical angle, and
the table of wet-line corrections.
4. Compute the true vertical depth by subtracting the wet-line
correction from the air-line corrected observed depth.
5. Air-line and wet-line corrections should be interpolated
from their respective tables to the nearest tenth of a foot.
All other computations and checking are essentially the
same for measurements with vertical angles as they are for stan-
dard discharge measurements, including the computation of
measurement standard error.
6.1.5.3 Moving Boat Measurements
Two types of moving boat measurements utilize a horizon-
tal axis current meter. The primary difference between these
two types of measurements is the data-recording method and
the computation method. The original type of moving boat mea-
surement is defined here as the manual method, and the more
recent type is defined as the automatic method. In the manual
method, some of the data are acquired by visual observation and
recording on paper field notes as the measurement progresses
across the stream. All computations in the manual method are
performed by hand calculator and look-up tables. In the auto-
matic method, almost all data collection, data recording, and
computations are performed by an on-board computer. The
manual method is still in use at the time of this report (2001),
however, it is rapidly being replaced by the automatic method.
Also, some moving boat measurements now utilize an acoustic
Doppler current profiler (ADCP) for measurement of stream
velocity. This method is described in section 6.1.5.5.
6.1.5.3.1 Moving Boat Measurement, Manual Type
The discharge measurement front sheet (summary) for the
manual type of moving boat measurement is different than the
standard current meter front sheet, but the differences are minor
and for practical purposes can be considered the same. There-
fore, entry of summary data and information for a manual type
of moving boat measurement should use the same entry form as
the standard current meter measurement (see table 4). A few
special items that show on the front sheet can be entered as part
of the inside of the measurement described below.
The inside notes of the manual type of moving boat mea-
surement are considerably different than those of a standard dis-
charge measurement. A typical inside note sheet is shown in
figure 2. The data columns required are as follows.
• Angle,
α
—The horizontal angle of the current meter is
read visually from an angle indicator as the boat
progresses across the stream.
• Depth—Depths at each vertical are taken from an
acoustic sounding chart.
• Pulses per second—These readings are instantaneous
values of current meter response, related to velocity,
taken visually from the rate indicator at each vertical.
• Remarks—The remarks column provides data and
information that relate to the individual verticals and
subsections.
6. Verification and Analysis of Field Measurement Data 31
Angle
α
L
b
Dist.
from
initial
point
Width Depth
Pulses
per
second
V
v
Sin α
V
v
Sin α
Area
Dis-
charge
Remarks
IP 0 IP to LEW=28’
LEW 28.0 19.5 0 0
20 39.0 67.0 36.0 9.0 250 4.50 .342 1.54 324 499
25 33.1 100.1 48.2 39.0 340 6.09 .423 2.58 1880 4850 (1/2 count)
30 63.2 163.3 63.5 38.0 370 6.62 .500 3.31 2410 7980
29 63.8 227.1 60.2 37.5 340 6.09 .485 2.95 2260 6670
39 56.7 283.8 56.3 37.0 340 6.09 .629 3.83 2080 7970
40 55.9 339.7 57.8 35.0 330 5.91 .643 3.80 2020 7680
35 59.8 399.5 57.8 35.5 330 5.91 .574 3.39 2050 6950
40 55.9 455.4 52.4 33.0 330 5.91 .643 3.80 1730 6570
48 48.8 504.2 48.8 32.5 350 6.27 .743 4.66 1590 7410
48 48.8 553.0 50.6 32.0 340 6.09 .743 4.52 1620 7320
44 52.5 605.5 50.2 31.5 340 6.09 .695 4.23 1580 6680
49 47.9 653.4 48.4 31.0 320 5.74 .755 4.33 1500 6500
48 48.8 702.2 52.4 30.0 330 5.91 .743 4.39 1570 6890
40 55.9 758.1 53.8 28.5 320 5.94 .643 3.69 1530 5650
45 51.6 809.7 52.5 26.5 300 5.38 .707 3.80 1390 5280
43 53.4 863.1 54.2 27.0 330 5.91 .682 4.03 1460 5880
41 55.1 918.2 50.5 27.0 350 6.27 .656 4.11 1360 5590
51 45.9 964.1 51.3 26.0 330 5.91 .777 4.59 1330 6100
39 56.7 1020.8 55.0 25.0 320 5.74 .629 3.61 1380 4980
43 53.4 1074.2 54.6 25.0 320 5.74 .682 3.91 1360 5320
40 55.9 1130.1 57.4 25.0 330 5.91 .643 3.80 1440 5470
36 59.0 1189.1 51.4 24.5 330 5.91 .588 3.48 1260 4380
53 43.9 1233.0 48.2 23.5 320 5.74 .799 4.59 1130 5190
44 52.5 1285.5 53.8 22.5 320 5.74 .695 3.99 1210 4830
41 55.1 1340.6 58.8 22.5 330 5.91 .656 3.88 1320 5120
31 62.6 1403.2 60.8 22.0 330 5.91 .515 3.04 1340 4070
36 59.0 1462.2 55.4 22.5 320 5.74 .588 3.38 1250 4220
19 51.8 1514.0 55.4 12.0 340 6.09 .326 1.99 665 1320 (3/4 counts)
REW 59.0 1573.0 29.5 0 0
FP 1596.0 REW to FP=23’
1545.0 1544.7 42,039 157,369
x1.022 x1.022 Width/Area
Width/Area Adjustment Coefficient: 1579 1545=1.022 Adj. Coef.
43,000 160,831
x .91 Vel.Corr.Coef.
146,000
Figure 2. Discharge measurement inside notes for manual type of moving boat measurement.
32 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
All other columns in the inside notes are computed and/or
determined from look-up tables. These are considered informa-
tion, not data, and after verifying that the data have been
entered correctly, the information columns should be checked
with the electronic processing system. This checking will
require that the electronic processing system have access to the
tables and equations used for moving boat measurements. Fol-
lowing are the information columns required.
• Boat travel distance, L
b
—Most of the L
b
values are
determined from the look-up table, based on the angle,
α, and range number used for the control panel during
the moving boat measurement. Special methods apply
for the determination of L
b
values at the beginning and
end of each run. The first L
b
value, corresponding to the
first measured angle, is an actual field measurement of
the distance from the edge of water to the float marker.
This measurement is a field data value, and should not
be changed. The second L
b
value, corresponding to the
second measured angle, always is entered as one-half of
the table value. The next-to-last L
b
value is entered on
the basis of the proportion shown in the remarks
column of the field notes. The last L
b
value is an actual
field measurement, and should not be changed. All L
b
values between the two points at each end of the mea-
surement are determined directly from the look-up
table. The total boat travel distance should be computed
as the sum of all subsection distances.
• Distance from initial point—These distances mostly
are computed values, and should begin at the edge of
water on one side of the stream and end at the edge of
water at the other side of the stream. The water edges
usually are designated LEW (left edge of water) and
REW (right edge of water). All distances are referenced
to an initial point (IP), which usually is designated as
having a distance of zero (0). A final point (FP) also is
included in the notes. The distance for the edge of water
at the beginning of the measurement is based on the
actual field measurement of the distance from the IP to
the edge of water. All other distances are computed by
adding Lb to the preceding distance.
• Width—These are incremental widths for each subsec-
tion, and are computed just as they are in a standard cur-
rent meter measurement, based on one-half the distance
from the preceding vertical to one-half the distance to
the next vertical. The total width should be computed as
the sum of all subsection widths.
• Vector velocity, V
v
—These are instantaneous vector
velocities, and are determined from the rating table (or
equation) for the current meter, and correspond to the
pulses per second recorded for each vertical.
• Sine of angle, Sine
α
—These values are the sine func-
tion values corresponding to the angle, α, for each ver-
tical.
• Product of V
v
and Sine
α
—The stream velocity normal
to the cross section, for each vertical, is computed as
the product of V
v
and sine α.
• Area—The subsection area is computed as the product
of the subsection width and the vertical depth, just as in
a standard current meter measurement. The total area
also should be computed as the sum of all subsection
areas.
• Discharge—The subsection discharge (unadjusted) is
computed as the product of the subsection area and the
normal stream velocity (see above). The total unad-
justed discharge also should be computed as the sum of
all unadjusted subsection discharges.
A number of individual data items and computations are
included in the inside note sheet, and should be entered to the
electronic processing system and/or checked for computational
accuracy. These items and computations are listed below and
grouped as data items and computations.
Data items:
• Run number—This number indicates the run number
for a series of runs.
• Control panel range number—This number is used to
determine the correct look-up table for determining L
b
.
• Measured width—This is the total measured width of
the stream, water's edge to water's edge.
• Velocity adjustment coefficient, k
v
—This is the vertical
velocity coefficient used to adjust the total discharge for
the effect of velocity measurements taken near the
stream surface.
• Distance from IP to beginning edge of water—This is
a measured distance.
• Distance from ending edge of water to FP—This is a
measured distance.
• Distance from beginning edge of water to initial
float—This is a measured distance.
• Distance from final float to ending edge of water—This
is a measured distance.
Computations:
• Width/area adjustment coefficient, k
b
—This coeffi-
cient is a computed value equal to the ratio of the mea-
sured stream width to the computed stream width.
• Total adjusted area—The total adjusted area is com-
puted by multiplying the total unadjusted area times the
coefficient, k
b
.
• Total adjusted discharge—The total adjusted dis-
charge is computed by multiplying the total unadjusted
discharge times the coefficient, k
b
, and times the coef-
ficient, k
v
.
6. Verification and Analysis of Field Measurement Data 33
6.1.5.3.2 Moving Boat Measurement, Automatic Type
Moving boat measurements increasingly are being made
with integrated computerized equipment, including an on-board
computer that is used for recording all data and fully computing
the discharge measurement. The body (inside) of the measure-
ment is stored in electronic format, and should be transferred
directly to the electronic processing system. The summary front
sheet information is similar to a standard discharge measure-
ment and can be entered by keyboard, except for those items
that can be transferred to the summary from the inside body of
the measurement. The same entry form, as for a regular current
meter measurement, should be used (see table 4).
6.1.5.4 Acoustic Doppler Current Profiler (ADCP) Measurements
The ADCP is used to define the complete (or nearly com-
plete) velocity profile in a stream vertical. This velocity profile
provides a much more accurate measure of the mean stream
velocity than other techniques where only one or two measuring
points are used, and sometimes adjusted by velocity coeffi-
cients. The ADCP can be incorporated into the moving boat
method of measurement, providing a fast, accurate type of dis-
charge measurement for wide and deep streams. This type of
measurement is fully computerized, with all data collected and
computed automatically.
Data and information from the ADCP measurement should
be transferred to the electronic processing system through an
interface. These data and information become the original,
archivable record. Summary information for the measurement
is much the same as for a regular discharge measurement and
can be entered using the same entry form (table 4).
6.1.5.5 Indirect Measurements
Indirect discharge measurements include slope area, con-
tracted opening, critical depth, culvert, step backwater, and
flow over dams and embankments. These types of measure-
ments are almost always made after a flood event, rather than at
the time of the flood event. Data collection, recording of field
notes, and computation procedures are appreciably different
than standard measurements made during a flood event. For
most indirect measurements, special computer programs are
used for the computations and detailed reports are prepared.
Entry of information from indirect measurements to the elec-
tronic processing system should include only the summary
information. The same entry form can be used as for a standard
discharge measurement (table 4).
6.1.5.6 Portable Weir and Flume Measurements
Measurements of low discharge can be made using a por-
table weir or flume. Various types of weirs and flumes are avail-
able for these measurements and usually are rated in the labora-
tory so that coefficients and discharge ratings are defined for
each. Field setup and measuring methods are described by
Rantz and others (1982), and are relatively simple and easy to
follow. After the weir or flume is installed and a sufficient
period of time is allowed for streamflow to stabilize, a series of
upstream head measurements are taken for a period of about 3
minutes. The average of these head measurements is used to
determine the discharge, either from a rating table (flume mea-
surement) or from an equation (weir measurement). Down-
stream head measurements usually are not taken because the
flume or weir is installed so that free fall or minimum backwater
results; thus, negating the need for downstream head measure-
ments.
Entry of the inside body of the discharge measurement is
relatively simple and includes only the weir or flume head data,
and the determined discharge. Some hydrographers enter this
information on the front sheet of the measurement, rather than
in the inside body. Regardless of where these notes are
recorded, the electronic processing system should provide a
form for entering the basic data and computations, and should
check the computations. The data and information required are
as follows.
• Head measurements—These are the individual obser-
vations of head. The recommended number of observa-
tions is about seven, one observation every 30 seconds
for a period of 3 minutes. However, this number can
vary and in some cases only one observation will be
recorded. The electronic processing system should
allow for at least 10 entries.
• Average head, h—This is an unweighted average of the
individual head observations. The electronic processing
system should calculate the average head, h, and com-
pare it to the entered value. If the two values are differ-
ent, a message to this effect should be given to the user.
The user should be allowed to select the average head
value for use in computing discharge.
• Discharge, Q—The discharge should be calculated,
either from a rating table or from an equation. Rating
tables and/or equations for standard weirs and flumes
should be included in the electronic processing system.
However, if they are not directly available, the user
should be allowed to enter one.
Entry of front-sheet information for weir and flume mea-
surements greatly is abbreviated from that of a standard dis-
charge measurement and is described in table 4.
6.1.5.7 Tracer-Dilution Measurements
Tracer-dilution discharge measurements are highly spe-
cialized techniques that utilize one of a number of different trac-
ers, different types of measurement equipment, and different
measurement methods. Data collection, recording, and calcula-
tion of measurement information varies depending on the
method and tracer used. Details of each type of tracer-dilution
measurement are described by Rantz and others (1982).
Although the methods are well standardized, it is not recom-
mended that complete details of tracer-dilution measurements
be entered to the electronic processing system. Summary infor-
34 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
mation from each measurement should be entered, according to
the details given in table 4.
6.1.5.8 Volumetric Measurements
Low flows sometimes are measured by diverting the flow
into a calibrated container, and measuring the time required to
fill, or partially fill, the container. If the container is filled com-
pletely, the flow volume equals the container volume. If the
container is partially filled, the flow volume equals the differ-
ence of the ending volume and the starting volume. This proce-
dure usually is repeated 3-4 times to improve accuracy of the
measurement. The discharge, in cubic feet per second, is com-
puted by dividing the total volume (sum of the volume measure-
ments from each repetitive run), in cubic feet, by the total time
of diversion (sum of the time measurements from each repeti-
tive run), in seconds.
Data entry from the inside field notes includes the follow-
ing:
•Total container volume, in cubic feet.
• Starting volume, in cubic feet, for each repetitive
run—This value should be equal to or greater than zero,
but less than the total container volume.
• Ending volume, in cubic feet, for each repetitive
run—This value should be greater than the starting vol-
ume, and equal to or less than the total container vol-
ume.
• Flow volume, in cubic feet, for each repetitive
run—This is the difference between the ending volume
and the starting volume, and must be equal to or less
than the total container volume.
• Fill time, in seconds, for each repetitive run.
•Total volume, in cubic feet—This is a summation of the
individual flow volumes of each repetitive run.
•Total time, in seconds—This is a summation of the
individual fill times of each repetitive run.
• Discharge, in cubic feet per second—This is the total
volume divided by the total time.
The electronic processing system should make the checks
and computations indicated above, and report any discrepan-
cies.
The procedure described above is used where the total
flow can be easily diverted into a container. In some cases, such
at a broad-crested weir or dam the flow may be too shallow to
measure using conventional methods, but volumetric measure-
ments may be applicable to small segments (samples) of the
flow. This is the volumetric-incremental sampling method. In
this method, volumetric flow measurements are made as
described in the preceding paragraphs at 5-10 subsections along
the weir or dam. The flow rate of each sample is increased by
the ratio of the subsection width to the sampled width to obtain
a flow rate for each subsection. The total flow of the stream is
the summation of the discharge rates of each subsection. The
electronic processing system should perform these computa-
tions from the input data and report any discrepancies.
Front sheet information is an abbreviated version of the
standard discharge measurement. Details are given in table 4.
6.1.5.9 Discharge Estimates
Low flows sometimes are estimated when no suitable mea-
suring method is available. Various techniques for estimating
the flow are used, which usually are described in the paper field
notes. It is not recommended that the details of making the esti-
mate be entered into the electronic processing system, because
they generally cannot be checked or verified, and the paper
notes are considered the original archivable record. A summary
of the measurement can be entered using the standard discharge
measurement entry form (see table 4), but abbreviated consid-
erably to accommodate only the information pertinent to the
estimate.
6.1.6 Rounding and Significant Figures
All data (actual field measurements) for discharge mea-
surements should be entered to the electronic processing system
with the same precision and significant figures as recorded in
the field notes. Table look-up values and calculated values
should be rounded to standard significant figures (table 2),
unless specified otherwise by the user. Exceptions to the stan-
dard significant figures are required for calculations of the sub-
section values of width, area, and discharge in the inside body
of the field notes, as follows.
• Subsection width—The width of each subsection
should be used and displayed as an unrounded value.
• Subsection area—Each subsection area should be
rounded and displayed with one additional significant
figure from that of the expected total area. For instance,
if the total area is expected to be between 10.0 and 99.9
ft
2
, the individual subsection areas should be rounded
and displayed to hundredths of a square foot.
• Subsection discharge—Each subsection discharge
should be rounded and displayed with one additional
significant figure over that of the expected total dis-
charge, similar to that described above for subsection
area. For instance, if the total discharge is expected to
be between 100 and 999, then each subsection dis-
charge should be rounded and displayed to the nearest
0.1 ft
3
/s.
All summary information for discharge measurements
should be rounded and displayed with significant figures that
conform to those listed in table 2, unless specified otherwise by
the user.
6. Verification and Analysis of Field Measurement Data 35
6.1.7 Summary of Discharge Measurements
Discharge measurement information and data from all
types of discharge measurements should be summarized in
chronological order, and grouped by water year, to provide a
history of the measurements. The basic format of the summary
output form should conform closely to the historical USGS
standard form 9-207. The items required for this form are listed
in table 10. In addition to the summary format (short-form) of
discharge measurements, an output format (long-form) that
includes all of the data and information entered for each mea-
surement, as shown in table 10, should be available to the user.
The user also should be able to define a custom output format
that only would include selected items.
Table 10. Discharge measurement items that should be shown in U.S. Geological Survey long-form output and in
short-form output (historical form 9-207)
Item Long-Form Output
Short-Form Output
(9-207)
Station identification number X X
Station name X X
Measurement sequence number X X
Date of measurement X X
Mean time of measurement X X
Time zone X X
Party X X
Mean gage height, inside gage X X
Mean gage height, outside gage X
Gage-height change X X
Gage-height change time X X
Stream width X X
Stream area X X
Mean velocity X X
Number of sections X X
Measured discharge X X
Rating number X X
Shift adjustment X X
Percent difference X X
Adjusted discharge X X
Adjustment method X X
Number of channels measured X
Measurement type X
Measurement location X
Observation method X X
Accuracy rating (field assigned) X X
Computed accuracy X X
36 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
6.2 Gage Datum Analysis
The gages at streamgaging stations are referenced to a per-
manent datum (zero level) that must be maintained as accu-
rately as possible throughout the lifetime of the station. In order
to maintain this accuracy, leveling is performed periodically to
check the gages and reference marks for vertical movement, so
that if appreciable movement is detected, corrections can be
made. Generally, leveling at gaging stations is performed once
every 2 to 4 years, but the time frame varies according to gage
stability conditions and other factors. For complete details of
leveling procedures for gaging stations, see Kennedy (1990).
Complete gage levels are recorded on paper field notes that
include all turning point elevations, instrument setup heights,
elevations of gage reference marks, and other miscellaneous
gage features. These notes also may include various adjust-
ments required to account for instrument error and closure
error. In some instances, the field notes may include more than
one level circuit, and a summary field note sheet is included that
shows average elevations for benchmarks, reference marks, and
other gage features. These paper field notes are the original lev-
eling notes, and are archived as part of the permanent record. It
is not required that the complete field notes be entered to the
electronic processing system.
The electronic processing system should provide for the
entry of a summary of the field notes for gage- datum leveling.
Data and information that should be entered to the electronic
processing system from leveling notes are listed in table 6. In
addition, established elevations should be entered for each
benchmark, reference mark, and other gage feature for refer-
ence and comparison purposes. For each set of level notes the
electronic processing system should perform datum error com-
parisons as described in section 6.2.2.
6.2.1 Established Elevations
All benchmarks, reference marks, reference points, gage
features, and other permanent points that may be referenced to
the gage datum should be included in a gage datum reference
list. Each mark, feature, and point should be given a short,
abbreviated name that conforms with the usual surveying termi-
nology, such as BM1 (Benchmark No. 1), BM2 (Benchmark
No. 2), RM1 (Reference Mark No. 1), WWCB (Wire Weight
Check Bar), IGRP (Inside Staff Gage Reference Point), and
OGRP (Outside Staff Gage Reference Point). For each gaging
station, the list will be different and the user should be allowed
to establish the initial list and add new points at any time. In
Control conditions X X
Control cleaned X
Time of control cleaning X
Gage-height change from cleaning X
Maximum stage indicator X
Minimum stage indicator X
Air temperature (degrees Celsius) X
Water temperature (degrees Celsius) X X
Base flow (Yes or No) X
Gage height of zero flow X X
Gage height of zero flow accuracy X X
Mean index velocity X
Mean auxiliary gage height X
Remarks X X
Table 10. Discharge measurement items that should be shown in U.S. Geological Survey long-form output and in
short-form output (historical form 9-207)—Continued
Item Long-Form Output
Short-Form Output
(9-207)
6. Verification and Analysis of Field Measurement Data 37
addition to the abbreviated names, an optional, short description
of each point should be included for easy reference. This
description also would provide a place to document the status
(active, abandoned, destroyed, and others) of benchmarks, ref-
erence marks, reference points, and other gage features.
Established elevations should be provided for each bench-
mark, reference mark, reference point, and gage feature. These
elevations generally are the initial elevation defined by levels
for each point when the gaging station was first established.
However, as new points and features are established at later
times in the life of the gaging station, these new established ele-
vations should be added to the reference list. Also, it is some-
times found that the elevation of a point or feature may have
changed so that the new elevation is considered reasonably per-
manent. The user should be allowed to make a change to the
established elevation, but the electronic processing system
should maintain a history of all elevation changes, along with
dates of change, and names of persons making the change. An
optional "remarks" entry should be allowed for the purpose of
describing the reason for making an established elevation
change. Established elevations should be maintained as perma-
nent "known,” or "given" elevations, and changes should not be
made arbitrarily. These elevations become the basis for datum
error comparisons, as described in section 6.2.2, and are the
basis for making datum corrections to gage readings.
6.2.2 Datum Error Comparisons
One of the permanent benchmarks or reference marks at a
gaging station usually is defined and referred to as the base
benchmark. This is the benchmark at the station considered to
be the most stable of the various marks that may be used for lev-
eling purposes. Leveling at the station usually will start at this
benchmark, using it as the base, and all other elevations are
computed from that base. The base benchmark should be main-
tained as a permanent base so long as it remains stable.
For each set of levels, comparisons should be made
between established elevations and elevations determined by
leveling, for each benchmark, reference mark, reference point,
and gage feature. The first, and primary, comparison should use
the base benchmark as the starting point for all computations.
6.2.2.1 Base Benchmark Comparisons
The first, and sometimes the only, comparison between
established elevations and elevations determined by leveling is
made using the established base benchmark as the starting point
to compute the elevations of other benchmarks, reference
marks, reference points, and gage features. This method of
comparison almost always conforms to the way the levels were
run, and the way level data are entered to the electronic process-
ing system. The electronic processing system should compute
the difference between the established elevation and the eleva-
tion found by leveling, for each benchmark, reference mark,
reference point, and gage feature. These differences should be
retained as part of the permanent record, and should be dis-
played to the user as part of the gage-datum summary.
If levels are field computed and entered to the electronic
processing system using a benchmark that is not designated as
the base, the user should be alerted. Various reasons may be
present as to why a designated base benchmark is not used. One
reason could be that the benchmark may have been damaged or
destroyed so that it is no longer a reliable mark. The user should
be given the option to allow the levels to remain as entered, with
no recomputation, or to designate a recomputation using the
established base benchmark if the base was included in the lev-
els.
6.2.2.2 Alternate Benchmark Comparisons
Instances may result where comparative elevations, using
alternate benchmarks as a base, are desired, even though the
designated base benchmark is still being used. The user should
be allowed to designate an alternate benchmark as a base, and
the electronic processing system should compute and display all
other elevations on this basis. These elevations should be con-
sidered temporary, or work-sheet computations for comparative
analysis only. If such comparisons reveal that a different bench-
mark should be designated as a new base, then the user should
be allowed to make the change, and the elevations computed
using this new base should be retained.
Recomputation of elevations cannot be made using the
original rod readings and instrument heights because these are
not entered to the electronic processing system. Therefore, the
recomputation must be based on relative differences between
the entered elevations of each benchmark, reference mark, and
other feature.
6.2.2.3 Rounding and Significant Figures
All elevations of benchmarks, reference marks, and gage
features usually are shown to thousandths of a foot in level
notes and level-note front sheets. This degree of precision may
not be justified for some gage features, gage heights of zero
flow, and ground elevations. It is recommended that the preci-
sion and significant figures conform to the commonly used
values shown in tables 4 and 5; however, the precision and sig-
nificant figures are optional and the electronic processing
system should retain the precision and significant figures
entered by the user.
6.2.2.4 Gage Datum Summary
A historical summary of benchmarks, reference marks,
and gage features should be maintained with the electronic pro-
cessing system. This summary should include the name and
abbreviation of each feature, a designation for the base bench-
mark, the original established elevations for all benchmarks and
features, the elevations determined by leveling for each set of
levels, the difference between the established elevation and the
elevation determined by leveling, and remarks for each feature.
The summary should be updated each time a new set of levels
is entered, showing the date of leveling, and the names of the
38 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
99111100 Example creek near Timbucktoo, SC
(Station ID Number) (Station name)
[B=Base benchmark; (xxx)=Difference from gage reading; R=Gage reset; BM=Benchmark; RM=Reference mark; RP=Reference point; OG=Outside gage;
IG=Inside gage; WWT=Wire-weight gage; Elev.=Elevation; —=No data]
Date of levels 10-12-42 06-18-44 03-21-47
Party DJS, VBS VBS, MBS JDC, DJS
Benchmarks Original Elev. Elevation Elevation Elevation Elevation Elevation Elevation
BM1 12.235 12.240 12.242
RM1 2.468 (B) 2.468 (B) 2.468 (B)
RM2 2.992 2.990 2.994
RP1 15.334 15.333 15.331
USC&GS 275 25.451 25.448 25.449
Other…
Gage Features
Instrument shelf 16.43 16.44 16.43
Bottom of well 0.34 0.37 0.33
Lower door sill 5.89 5.89 5.88
Lower intake 0.75 0.76 0.76
Upper intake 1.79 1.79 1.80
Point of zero flow 0.23 0.30 0.20
Orifice —
Gages
OG 3.3 - 6.8 4.500 (-0.002) 4.501 (+.001) 4.530(+.030)
4.504(+.004)R
IG 0.0 - 6.8 3.480 (+0.004) 3.492 (+.012) 3.478 (-.002)
WWT check bar 19.673 19.660 19.662
Elec. tape index 16.532 16.532 16.530
Steel tape RP 16.687 16.691 16.688
Other…
Remarks
Gage establ.
OG reset
History and summary of gaging station levels
leveling party. An example of a datum summary is shown in
figure 3.
6.3 Crest-Stage Gage Analysis
Crest-stage gages are vertical pipes containing a rod or
wooden stick, and powder or dust such as cork dust. When
water enters the intakes at the bottom of the pipe, it rises to a
level corresponding to the outside water level until it reaches the
peak stage and then recedes, leaving a line of cork dust on the
rod/stick at the peak water level. The gage is designed so that
measurements, either from the top of the rod/stick or the bottom
of the rod/stick to the line of cork dust, can be used to compute
the peak stage. Sometimes, more than one peak will occur
between gage visits; thereby, leaving more than one crest mark
on the rod/stick. Special paper field notes are used to record the
information for a crest-stage gage.
Crest-stage gages may be the primary gage at a site where
only peak stage data are collected. A crest-stage gage also may
be used as an auxiliary gage at a continuous record gage site. In
either case, the same paper field note form is used at both types
of gage sites. The paper field notes are the original data used for
archiving. A summary of the data and information on the notes
should be entered to the electronic processing system as shown
in table 7. Checking and comparisons should be performed as
indicated in sections 6.3.1 and 6.3.2.
Figure 3. Example of a streamflow station datum summary.
6. Verification and Analysis of Field Measurement Data 39
6.3.1 Arithmetic Checking
Only one type of computation is made for crest-stage
gages on the field notes. This is the computation of the peak
stage for each crest mark entered on the form. The electronic
processing system should check this computation by adding the
measured distance of the crest mark to the index gage height for
gages where the index mark is at the bottom of the rod/stick. If
the index mark is at the top of the rod/stick, the measured dis-
tance of the crest mark should be subtracted from the index gage
height. The calculated crest-gage height should be compared to
the entered crest-gage height; if a difference is found the user
should be alerted so that changes can be made, if necessary.
6.3.2 Logic and Consistency Comparisons
The electronic processing system should make the follow-
ing comparisons to confirm that the data and information
entered for each crest mark are consistent and logical for the
given gage setup.
• Date comparison—The date estimated for the crest
mark normally should fall between the date of the pre-
vious and current gage visit. The electronic processing
system should make this comparison, and if the esti-
mated date does not fall between the two visits, the user
should be alerted and given the opportunity to make a
change. It is not mandatory that the estimated date fall
between the two visits. Circumstances may result to
cause the apparent discrepancy.
• Maximum gage-height comparison—The computed
crest-gage height should be compared to the maximum
possible gage height for the crest-stage gage. If the
computed gage height is greater, the user should be
alerted and given the opportunity to make necessary
changes.
• Minimum gage-height comparison—The computed
crest-gage height should be compared to the minimum
possible gage height for the crest-stage gage. If the
computed gage height is less than the minimum, the
user should be alerted and given the opportunity to
make necessary changes.
• Crest sequence comparisons—The cork dust marks
that are deposited on the rod/stick are fairly fragile, and
can be erased by subsequent peaks that exceed a mark.
When two or more marks are entered from one set of
field notes, the electronic processing system should
make a sequence comparison. The highest crest-gage
height should have the earliest estimated date of occur-
rence, the second highest crest-gage height should have
an estimated date that is later than the highest crest-
gage height, and the third highest crest-gage height
should be later than the previous one. The lowest crest-
gage height in the sequence should have the latest esti-
mated date. Although the previous description is the
normal sequence of marks, circumstances can result
where a mark still may be visible that is exceeded by a
higher peak, and may be measured and entered in the
field notes. The electronic processing system should
alert the user about any sequence discrepancies and
given the opportunity to make changes.
6.3.3 Rounding and Significant Figures
The precision of crest-gage heights usually is hundredths
of a foot. However, some marks may be measured only to the
nearest tenth of a foot. In such cases, the precision of individual
marks should be retained as entered to the electronic processing
system.
6.3.4 Summary of Crest-Stage Gage Measurements
A summary of all crest-stage gage measurements should
be listed in chronological order, and grouped by water year. The
summary listing should include all items shown in table 11.
6.4 Cross Sections
Cross-section data have various uses, but are primarily
intended as an aid in rating-curve analysis. One or more cross
sections may be entered with specific identifying information
that make them unique to a particular gage site. The data and
information entered for each cross section are listed in table 8.
Some of the checking and computations that should be per-
formed with the electronic processing system are listed in sec-
tions 6.4.1 through 6.4.3.
6.4.1 Logic and Consistency Checking
Cross-section entry consists mainly of transverse station-
ing along the line of the cross section, and ground elevations at
each station. Station distances are measured from an initial
point located on the left bank of the stream. The electronic pro-
cessing system should check that each station distance is equal
to or greater than the preceding station distance. The electronic
processing system also should insure that ground elevations are
provided for each station. Negative values of stationing and
ground elevations are acceptable.
6.4.2 Graphical Review
The user should be required to view a graphical plot of
each cross section to review and edit for inconsistencies and
data-entry errors. The plot should be drawn to a scale ratio of 5
horizontal to 1 vertical, with an option to change the scale, if
necessary. The plot should include all ground points, vertical
subdivision boundaries, if entered, horizontal roughness bound-
aries, if entered, and Manning roughness coefficients, if
entered. A typical cross-section plot is shown in figure 4.
40 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
Table 11. Crest-stage gage items that should be shown in the summary output form
[Items 9–12 should be arranged in tabular format, with multiple entries, if necessary, to accommodate multiple highwater marks.]
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Station identification number
Station name
Party
Date of crest-stage gage inspection
Crest-stage gage identification (for example, upstream gage, downstream gage, and others)
Gage height on date of inspection
Time of gage-height reading
Time zone
Type of gage read (for example, outside gage, inside gage, wire weight, and others)
Elevation of crest-stage gage reference point (top of rod/stick, bottom pin, and others)
Measured distance from crest-stage gage reference point to high watermark
Highwater mark elevation (calculated from items 9 and 10)
Highwater mark elevation, determined from outside highwater marks
Estimated date of highwater mark
Remarks
+
+
+
+
+
+
+
+
+
+++
+
+
Left bank Right bank
n=Manning roughness coefficient
n=0.03
n=0.045
n=0.04
n=prorated
n=prorated
n=0.06
n=0.06
Horizontal distance (not to scale)
Vertical distance (not to scale)
Figure 4. Typical stream cross-section plot.
7. Rating Curves 41
6.4.3 Computation of Cross-Section Hydraulic
Properties
The electronic processing system should provide for com-
putation of cross-section hydraulic properties, using standard
WRD methods, as described by Dalrymple and Benson (1967).
A computer program such as Hydraulic Information Exchange
(HYDIE), developed by Fulford (1993), can be used to compute
cross-section properties. These computations should be
optional, and not required for every cross section. The details
for computing the various cross-section properties will not be
described here, however, a typical summary listing of cross-
section properties is shown in table 12.
6.4.4 Rounding and Significant Figures
All data entered for cross sections should conform to the
precision given in table 1, and all computed information for
cross sections should be rounded to the precision given in table
2. The user should have the option to change the standard pre-
cision, as required, and numbers entered with a non-standard
precision should be retained as entered.
7. Rating Curves
Rating curves are relations between dependent and inde-
pendent variables. For instance, a rating curve expressing the
mathematical or graphical relation between stage (independent
variable) and discharge (dependent variable) is referred to as a
stage-discharge relation. The processing of most surface-water
records requires the application of one or more rating curves.
This section of this report will describe the various types of
rating curves, the methods of rating curve development, the
methods of rating curve entry to the electronic processing sys-
tem, and other related aspects of rating curves as they apply to
the electronic processing system.
Rating curves are an integral part of the computation of
most streamflow records, and become a part of the permanent
records for each station. However, the electronic processing
system also should allow the entry, development, and display of
rating curves independent of computing streamflow records for
specific gaging stations. That is, the user should be allowed to
use the rating curve aspects of the electronic processing system
and choose any one of the rating types listed below for entering,
editing, developing, refining, and experimenting with the data.
7.1 Types of Rating Curves
A number of rating curve types are available for the pro-
cessing of surface-water records. Following is a brief descrip-
tion of each type.
• Stage-discharge relation—This type of rating is the
most common rating used for the processing of surface-
water records. It is a relation between water-surface
gage height and the rate of flow of the stream. Much of
the descriptive information about rating curves that
follow in this report will be discussed in terms of stage-
discharge relations; however, many of the basic princi-
ples, entry procedures, plotting procedures, and other
Table 12. Summary of calculated cross-section properties that should be listed in tabular format
[ft, foot]
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Station identification number
Station name
Date of cross-section survey
Party
Cross-section identification number (a sequential number unique for each cross section)
Location of cross section (longitudinal stationing, in feet, relative to the gage)
Type of control that cross section represents, if applicable (for example, section control or channel control)
Gage height, incremented according to user specifications (for example, 0.5 ft intervals, 1.0 ft intervals, 2.0 ft intervals)
Number of sub-areas
Total cross-section top width
Total cross-section area
Total cross-section conveyance
Wetted perimeter
Hydraulic radius
Critical discharge
Maximum depth (for natural sections), or head (for weirs and flumes).
Mean depth
Remarks
NOTE—For each cross section, items 8–12 should be arranged in tabular format, beginning with the lowest specified gage height and incre-
mented at the specified interval to the highest specified gage height.
42 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
processing methods also are applicable to the other
types of ratings. For stage-discharge ratings, the mini-
mum allowable discharge is zero. Also, discharge
values always should increase as gage height increases.
• Stage-area relation—This is a relation between gage
height and area for a standard cross section of the
stream. This type of rating commonly is used for veloc-
ity-index methods of computing discharge. Cross-sec-
tion area always should increase as gage height
increases. The minimum value of area is zero, and neg-
ative values of area are not permitted.
• Velocity-index and mean velocity relation—This is a
relation between an index velocity (electromagnetic,
acoustic, and others) and the mean velocity for a stan-
dard cross section of the stream. This type of rating
commonly is used for velocity-index methods of com-
puting discharge. The mean velocity usually increases
as the index velocity increases, but sometimes may
decrease. Negative values of either parameter, the
velocity index or the mean velocity, are permitted; most
velocity ratings of this type will extend into the nega-
tive range. For this reason, logarithmic ratings are
seldom used for this type of rating.
• Stage and velocity factor relation—This is a relation
between gage height and an adjustment factor used in
the velocity-index method of computing discharge. The
adjustment factor almost always increase as stage
increases, but in some instances it will decrease. It
always should be a positive value.
• Stage-fall relation—This is a relation between gage
height and the water-surface fall between the base gage
and an auxiliary gage. This relation is used in the slope
method of computing discharge. Fall may increase or
decrease as stage increases, but it always should be a
positive value. Negative values of fall should not be
allowed.
• Fall ratio and discharge ratio relation—This is a rela-
tion between the fall ratio, F
m
/F
r
, and discharge ratio,
Q
m
/Q
r
, as used in the slope method of computing dis-
charge. The discharge ratio always should increase as
the fall ratio increases. Neither ratio should be negative.
The upper limit of both ratios usually is less than 1.5,
but in rare cases may exceed 1.5.
• Stage-1/US
c
relation—This is a relation between gage
height and a flood-wave factor, 1/US
c
, and is used in the
rate-of-change in stage method of computing dis-
charge. The flood-wave factor may increase or decrease
as stage increases, however, it always should be a posi-
tive value.
• Elevation and reservoir contents relation—This is a
relation between the water-surface elevation of a reser-
voir and the contents of the reservoir. The reservoir
contents always should increase as elevation increases,
and always should be a positive value. The minimum
allowable value for reservoir contents is zero. This
rating should allow for large numbers, with reservoir
contents sometimes exceeding 4,000,000 acre-feet and
elevation sometimes exceeding 6,000 ft above sea level.
Elevation usually is shown to a precision of hundredths
of a foot (for example, 2,345.67).
Gaging stations at control structures such as dams require
a number of different rating curves and rating equations for
spillways, gates, turbines, and other flow conveyances. These
ratings specifically are designed for each individual structure
and are a part of the structure computation program, as
described by Collins (1977).
The BRANCH model method for computation of stream-
flow records does not require the use of individual rating
curves. That model has internal calibration procedures as
described by Schaffrannek and others (1981).
All ratings may be defined as logarithmic plots, linear
plots, or equations. A summary of rating curve characteristics,
limitations, and requirements is given in table 13. All ratings
should be tested with the requirements and limitations listed in
table 13.
7. Rating Curves 43
7.2 Rating Selection Default Procedure
When a user is working on a specific gaging station with a
specific computation method defined, and where ratings may,
or may not, already be defined, the electronic processing system
automatically should default to the rating type applicable to the
defined computation method. For instance, if the computation
method is stage-discharge, then the electronic processing
system should default to a stage-discharge rating, or if a slope
computation method is required, then the electronic processing
system should default to the three rating types applicable to
slope stations (stage-discharge, stage-fall, and fall ratio-dis-
charge ratio ratings). The electronic processing system should
not allow a rating type to be entered for a gaging station other
than those applicable to the defined computation method for
that station.
Stage-discharge ratings are the most commonly used rat-
ings, and should, therefore, be the default rating of choice when
the rating procedure is used independently; that is, not in con-
junction with a specific gaging station.
7.3 Entry of Rating Curve Information
Rating curve information required for defining the relation
between the independent and dependent variables, such as gage
heights and discharges, can be entered into the electronic pro-
cessing system using various methods, including tabular, equa-
tion, and graphical methods. Tabular entry is the use of a table
of descriptor data pairs, each representing a specific location of
the rating curve. Equation entry is the use of a mathematical
expression to define the rating curve algebraically. Graphical
entry is a method whereby a series of points are entered directly
on a rating curve plot displayed on the computer monitor, and
the electronic processing system automatically evaluates the
points, connects the points, and displays the rating curve.
Tabular entry and graphical entry are similar in that both
utilize user-defined descriptor points. The primary difference is
that tabular entry is based on descriptor points that are hand
picked from a paper rating curve plot, whereas graphical entry
is based on descriptor points defined on the computer monitor,
thus, negating the need for a paper plot. An individual rating
curve can be entered by using only one or the other of these two
entry modes, or in combination. However, the electronic pro-
cessing system should not allow either of these entry modes to
Table 13. Rating curve characteristics, limitations, and requirements
[1/US
c
, Boyer coefficient]
Computation
Method
Rating Type
Independent Variable
Plot Scale
Preference
Minimum
Value
Allowed
Maximum
Value
Allowed
Negative
Values
Allowed
Rating
Reversals
Allowed
Dependent Variable
Stage—discharge Stage—
discharge
Gage height Ordinate No limit No limit Yes No
Discharge Abscissa Zero No limit No
Velocity Stage—
area
Gage height Ordinate No limit No limit Yes No
Area Abscissa Zero No limit No
Index velocity
and mean
velocity
Index velocity Ordinate No limit No limit Yes Yes
Mean velocity Abscissa No limit No limit Yes
Stage and
velocity
factor
Gage height Ordinate No limit No limit Yes Yes
Velocity factor Abscissa Zero No limit No
Slope
1
Stage—fall Gage height Ordinate No limit No limit Yes Yes
Water-surface fall Abscissa Zero No limit No
Fall ratio and
Q ratio
Fall ratio Abscissa Zero 1.5 No No
Discharge ratio Ordinate Zero 1.5 No
Change in stage
1
Stage—1/US
c
Gage height Ordinate No limit No limit Yes Yes
Factor, 1/USc Abscissa Zero No limit No
Reservoir Elevation—
contents
GHt or elevation Ordinate No limit No limit Yes No
Reservoir contents Abscissa Zero No limit No
1
Requires a stage-discharge rating in addition to rating types shown.
44 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
be used in combination with the equation mode of entry. The
requirements for each type of entry mode are described in sec-
tions 7.3.1 through 7.3.3.
7.3.1 Tabular Entry
Rating curves may be entered to the electronic processing
system by keyboard as a series of descriptor points, sometimes
referred to as point pairs. Each point pair contains the indepen-
dent variable and the corresponding dependent variable for one
position on the rating curve. The electronic processing system
should not limit the number of point pairs that can be entered.
Point pairs always should be entered in ascending order of the
independent variable, starting with the lowest point on the
rating curve. If the user incorrectly enters a point pair in which
the independent variable is not ascending, the electronic pro-
cessing system immediately should issue a warning message to
alert the user that an entry error was made. This checking
method also should be used for the dependent variable for those
ratings where the dependent variable is not allowed to decrease.
A similar warning message also should be given if negative
values are entered for ratings where they are not allowed.
Rating curves that are entered as linear scale ratings will
require only the table of point pairs. No other descriptive infor-
mation is needed for either plotting or expanding (interpolating)
a linear scale rating.
Rating curves entered as logarithmic scale ratings will
require entry of scale offset information, in addition to the table
of point pairs. A scale offset is a value that is subtracted from
the independent variable before interpolating between point
pairs of the rating. It is important that the scale offset entered at
this point is the same as the one used for the plotted rating curve.
Because there is no way to verify that the offset used for a paper
plot and the entered offset are the same, the electronic process-
ing system should include a reminder at the point of offset entry,
that states, “Offsets entered here must be identical to offsets
used for the rating curve plot to provide exact duplication in the
rating table.” If the user does not enter a scale offset for a loga-
rithmic rating, the electronic processing system should not
accept the rating, and should prompt the user that an offset is
required.
The electronic processing system should allow one, two,
or three scale offset values for each logarithmic rating curve,
with each respective offset applicable to a designated range, or
segment, of the rating. The offsets should be entered starting
with the lowest rating curve segment and progressing upward,
with a defined breakpoint between successive offsets. The
breakpoint is the value (usually gage height) of the independent
variable above which the succeeding offset should be used. The
following combinations of offsets and breakpoints are allow-
able.
• One offset, no breakpoints—In this case, a single offset
is used throughout the range of the rating.
• Two offsets, one breakpoint—In this case, the first
offset is used for all values of the independent variable
that are less than or equal to the breakpoint value. The
second offset is used for all values of the independent
variable that are equal to or greater than the breakpoint
value.
• Three offsets, two breakpoints—In this case, the first
offset is used for all values of the independent variable
that are less than or equal to the first breakpoint value.
The second offset is used for all values of the indepen-
dent variable that are equal to or between the first and
the second breakpoints. The third offset is used for all
values of the independent variable that are equal to or
greater than the second breakpoint value.
A point pair entry in the table of point pairs is required at
each breakpoint of the rating. If the user omits the point pair
corresponding to a breakpoint, the electronic processing system
should issue a warning message and should not accept the rating
unless this requirement is met. The point pair at each breakpoint
is used as the ending point for the rating-curve segment below
the breakpoint, and the beginning point for the rating-curve seg-
ment above the breakpoint This process insures continuity of
the rating-curve segments. Scale offsets are described in more
detail in section 7.7.6.2.
7.3.2 Equation Entry
Some ratings may be easily expressed in equation form,
and if so, they may be entered to the electronic processing
system as a mathematical expression. Such ratings usually are
of simple form, consisting of a smooth curve or straight line,
with no unusual shapes or sharp bends. For all equation ratings,
a basic format as given in equation 21 should be used.
(21)
where
Y = dependent variable (usually discharge),
X = independent variable (usually gage height),
a = equation constant (default value is zero),
b = multiplier (default value is 1),
e = scale offset (default value is zero),
c = exponent (default is 1).
Equation 21 can be used for rating curves interpolated
either linearly or logarithmically. Other types of equations, such
as parabolic equations, are not recommended for surface-water
rating curves.
Upper and lower equation limits also should be required as
part of the input for equation ratings. These limits should, by
default, be in terms of the independent variable; however, the
user should have the option to specify the limits in terms of the
dependent variable. When extrapolation of equation ratings is
needed, and can be justified, a modification of the approved
limits should be allowed. The electronic processing system
automatically should not extrapolate the equation beyond the
approved specified limits.
YabXe–()
c
+=
7. Rating Curves 45
The electronic processing system should allow up to three
equations for the definition of a rating curve. Breakpoints, in
terms of the independent variable, between two consecutive
equations are required to define the exact point of the ending of
one equation and the beginning of the next equation. Consecu-
tive equations must intersect at the given breakpoint. The elec-
tronic processing system should calculate the dependent vari-
able at the breakpoint by using each equation, and if the two
calculated values of the dependent variable are not identical the
electronic processing system should alert the user and not
accept the equations until appropriate changes are made. These
checks and modifications should be made at the time of equa-
tion entry, and before application of the equations.
When multiple equations are used to define a rating curve,
a lower limit should be specified for the lower equation, and an
upper limit should be specified for the upper equation. The
same rules and guidelines apply to these limits as stated previ-
ously for single equation limits.
7.3.3 Graphical Entry
Graphical input of rating curves is presently the most auto-
mated and preferred method of entering a rating curve to the
electronic processing system. Historically, rating curves have
been drawn manually on paper work sheets, and descriptor
points visually are read from the plot. The electronic processing
system should provide a method whereby the user can automat-
ically plot, from the electronic processing system files, selected
discharge measurements and other rating curve information on
the computer monitor, and then fit a rating curve to the plotted
points directly on the monitor. The fitting process will be done
by specifying a series of descriptor points, either directly on the
computer monitor or in a table displayed on the monitor. After
the user is satisfied with the accuracy and smoothness of the
rating curve, the electronic processing system should automati-
cally transform the plotted rating curve into a rating table.
7.4 Rating Tables
The rating table is primarily for the purpose of displaying
values of the dependent variable for the complete range of the
independent variable. Rating tables should be generated with
the electronic processing system for all rating curves. The tables
are populated by interpolating values of the dependent variable
for the complete range of the independent variable, at intervals
equal to the stated precision of the independent variable or other
user-defined interval. For instance, if the independent variable
is gage height, and its stated precision is hundredths of a foot,
then values of the dependent variable (for example, discharge)
would be computed for every hundredth of a foot of gage height
for the full range of gage height defined by the limits of the rat-
ing. The interpolation methods and other requirements of pro-
ducing rating tables are described in sections 7.4.1 through
7.4.5.
7.4.1 Interpolation Methods
The method used to interpolate between rating input points
should be based on the method used to develop the rating.
Rating curves defined as linear scale ratings should be interpo-
lated between input points using a simple linear interpolation
method.
Rating curves defined as logarithmic scale ratings should
be interpolated between log-transformed input points using a
linear interpolation method. The applicable scale offset must be
subtracted from all input values of the independent variable
before making the logarithmic transformations. If the rating is
defined with two or three scale offsets, then each offset only
should be applied within the range defined by the respective
breakpoints.
It is very important that the interpolation process use the
same offset, or offsets, that are used for the development of the
rating curve plot, so that the resulting rating table precisely
duplicates the plotted curve. If the rating is plotted on the elec-
tronic processing system monitor, the rating curve automati-
cally is converted to a rating table, and the offset will automat-
ically be the same for both the plotted curve and the resulting
table. If the rating curve is entered as a table of descriptor
points, then the interpolation method must use the scale offset,
or offsets, entered with the descriptor points. The user is respon-
sible for insuring that the offsets are identical.
Note that the subtraction of the scale offset from the inde-
pendent variable is made only for the purpose of transformation
and interpolation. The subtraction should not alter the original
values of the independent variable that are displayed in the
rating table or plotted on rating curve plots.
The dependent variable (for example, discharge) for many
rating curves has a minimum value of zero, which theoretically
cannot be transformed to a logarithm. A simple linear interpo-
lation between the zero point and the next larger input value of
the dependent variable should be used for logarithmic ratings
beginning with zero. To avoid appreciable distortion of the low
end of the rating, it is recommended that the input value of the
dependent variable that follows the zero input value be equal to
or less than 0.1. The electronic processing system should issue
a warning message to the user if 0.1 is exceeded, and provide an
opportunity to make changes.
The independent variable (for example, gage height) can
sometimes be zero or negative at the low end of a rating curve.
This value is permissible only when subtraction of the scale
offset from the independent variable results in a positive num-
ber. See section 7.7.6.2.1 for additional details.
Rating curves defined by one or more equations also
should be transformed into rating tables. This is a simple
method of computing the dependent variable for the entire
range of each equation, as defined by the breakpoints and input
limits.
46 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
7.4.2 Rating Table Precision and Significant Figures
Rating tables should be defined and displayed using either
standard precision or expanded precision methods. Standard
precision involves using only the number of significant figures
required for each variable as defined in tables 1 and 2.
Expanded precision involves the addition of one additional sig-
nificant figure for the dependent variable. For instance, if the
standard number of significant figures for the dependent vari-
able (for example, discharge) is three, then standard precision
would display three significant figures and expanded precision
would display four significant figures.
7.4.3 Rating Table Smoothness Analysis
One method of analyzing the smoothness of a rating curve
and/or rating table can be done by studying the differences
between successive values of the dependent variable. To make
this task easy for the user, the rating table should display the
computed differences (traditionally referred to as first differ-
ences) of the dependent variable between every tenth value of
the independent variable displayed in the rating table. For
instance, if gage height is incremented every 0.01 ft in the rating
table, then the difference between discharges corresponding to
gage heights at 0.1 ft intervals should be computed and dis-
played.
7.4.4 Other Rating Table Information
The rating table should include descriptive information
that identifies the gaging station, type of rating, period of use,
and other items that are unique for that rating. At a minimum,
the following items should be included in the table.
• Station number—The downstream order number that
identifies the station.
• Station name—The official name of the station.
• Rating table number—The unique number assigned to
identify the rating table.
• Processing information—The time and date the rating
was entered, and name of the person making the entry.
If the rating is edited (minor changes only) or extrapo-
lated and the rating number is not changed, then addi-
tional times, dates, and names should be shown that
identify when these changes were made. Information
explaining a change, or extrapolation, can be given in
the narrative rating description (see descriptions
below).
• Type of rating—The rating type, such as stage-dis-
charge, stage-area, and others. This rating type also will
identify the input parameter (independent variable) and
the output parameter (dependent variable). The units of
measurement (for example, feet, cubic feet per second,
square foot, and so forth) should be shown for the inde-
pendent and dependent variables.
• Method of rating definition—The method by which the
rating is defined, either logarithmic plot, linear plot, or
equation.
• Scale offset, or offsets (for logarithmic ratings
only)—The scale offset(s) used for the working plot of
the rating.
• Scale offset breakpoints (for logarithmic ratings
only)—The value of the independent parameter that
defines the point of change from one scale offset to the
next. Breakpoints only are required if the rating is
defined with more than one scale offset.
• Period of use—The date, time, and time zone that iden-
tifies the beginning and ending of the period of time for
which the rating is to be used. If the rating is still in use,
then the ending date, time, and time zone should be left
open.
• Rating description (optional)—A narrative description
of the rating definition. This is an optional entry at
which point the user can describe how the rating was
defined, the number of measurements used, strong and
weak points of the rating, how the rating was extrapo-
lated (if done), use of theoretical methods in developing
the rating, and any other information that might qualify
the rating.
• Significant figures—The use, or non-use, of expanded
precision should be identified.
• Input values—If the rating was entered using descriptor
points, each of the entered points should be identified in
the body of the table. This traditionally has been done
by flagging each entered point with an asterisk (*).
An example of an expanded rating table for a logarithmic
stage-discharge rating curve is shown in figure 5. This sample
rating table illustrates the header information and a typical
arrangement of table information.
7.5 Rating Curve Numbers
Every rating curve for a specific gaging station should be
identified with a number. The preferred numbering system
should be a simple, consecutive number, with the earliest used
rating as number 1, the next rating number 2, and so forth.
Although not recommended, alpha-numeric numbers should be
permitted, as well as decimal number combinations such as 3a.2
or 4.2b. Gaging stations with long periods of record may have
old ratings that either are identified only by dates of use, or con-
secutive numbers. These older ratings may no longer be in use,
and in many cases may not be entered to the electronic process-
ing system. It is recommended, however, that the old numbers
be retained whenever possible, and that newer ratings that are
entered to the electronic processing system be numbered in the
same sequence. Changing original rating numbers, breaking the
numbering sequence, or using duplicate numbers for different
ratings at a gaging station, should be avoided, if possible.
7. Rating Curves 47
UNITED STATES DEPARTMENT OF THE INTERIOR—GEOLOGICAL SURVEY—WATER RESOURCE DIVISION
EXPANDED PRECISION RATING TABLE TYPE: LOG
RATING NO: 001 [10-01-1996] Scale offset=1.00
USGS 99410000 COMPUTER PROCESSED: 03-20-1997 BY vbsauer
Alabama River stage-Q test site
BASED ON ___DISCHARGE MEASUREMENTS, NOS___, AND ___, AND IS___WELL-DEFINED BETWEEN___AND___CFS
RATING ANALYSIS BY _____________________DATE__________RATING
DESCRIPTION______________________________________________________________________________________________________
GAGE
EIGHT
(FEET)
DISCHARGE, IN CUBIC FEET PER SECOND DIFF IN
Q PER
TENTH
FT
.00 .01 .02 .03 .04 .05 .06 .07 .08 .09
3.00
3.10
3.20
3.30
3.40
2.000*
2.998
4.337
6.346
8.346
2.086
3.115
4.493
6.294
8.602
2.175
3.236
4.653
6.501
8.864
2.267
3.360
4.817
6.713
9.132
2.362
3.489
4.985
6.930
9.406
2.460
3.620
5.158
7.152
9.687
2.561
3.756
5.336
7.379
9.974
2.666
3.895
5.518
7.613
10.27
2.773
4.039
5.705
7.851
10.57
2.884
4.186
5.896
8.096
10.87
.998
1.339
1.756
2.253
2.844
3.50
3.60
3.70
3.80
3.90
11.19
14.71
19.03
24.26
30.52
11.51
15.11
19.51
24.84
31.21
11.83
15.51
20.00
25.43
31.91
12.17
15.92
20.50
26.02
32.62
12.51
16.34
21.01
26.63
33.34
12.86
16.77
21.53
27.25
34.08
13.21
17.20
22.05
27.88
34.83
13.58
17.65
22.59
28.53
35.59
13.95
18.10
23.14
29.18
36.36
14.33
18.56
23.69
29.84
37.15
3.520
4.320
5.230
6.260
7.430
4.00
4.10
4.20
4.30
4.40
37.95
46.68
56.88
68.69
82.30
38.76
47.63
57.98
69.97
83.76
39.58
48.60
59.10
71.26
85.25
40.42
49.58
60.24
72.58
86.75
41.28
50.58
61.40
73.91
88.28
42.14
51.59
62.57
75.26
89.83
43.02
52.61
63.76
76.63
91.39
43.92
53.66
64.97
78.02
92.98
44.82
54.71
66.19
79.42
94.59
45.75
55.79
67.43
80.85
96.22
8.730
10.20
11.81
13.61
15.57
4.50
4.60
4.70
7.80
4.90
97.87
115.6
135.7
158.4
183.8
99.54
117.5
137.8
160.8
186.5
101.2
119.4
140.0
163.2
189.2
103.0
121.4
142.2
165.7
192.0
104.7
123.3
144.4
168.2
194.8
106.5
125.3
146.7
170.7
197.6
108.2
127.4
149.0
173.3
200.5
110.0
129.4
151.3
175.9
203.4
111.9
131.5
153.6
178.5
206.3
113.7
133.6
156.0
181.1
209.3
17.73
20.10
22.70
25.40
28.50
5.00
5.10
5.20
5.30
5.40
212.3
244.0
279.2
318.1
361.1
215.3
247.3
282.9
322.2
365.7
218.3
250.7
286.6
326.4
370.2
221.4
254.1
290.4
330.6
374.8
224.5
257.6
294.3
334.8
379.5
227.7
261.1
298.2
339.1
384.2
230.9
264.6
302.1
343.4
389.0
234.1
268.2
306.0
347.8
393.8
237.3
271.8
310.0
352.2
398.6
240.6
275.5
314.1
356.6
403.5
31.70
35.20
38.90
43.00
47.30.
5.50
5.60
5.70
5.80
5.90
408.4
460.3
517.1
579.1
646.6
413.4
465.8
523.1
585.6
653.7
418.4
471.3
529.1
592.1
660.8
423.5
476.8
535.1
598.8
668.0
428.6
482.4
541.3
605.4
675.2
433.8
488.1
547.4
612.1
682.6
439.0
493.8
553.6
618.9
689.9
444.2
499.5
559.9
625.8
697.3
449.5
505.3
566.3
632.7
704.8
454.9
511.2
572.7
639.6
712.4
51.90
56.80
62.00
67.50
73.40
6.00
6.10
6.20
6.30
6.40
720.0*
780.8
845.1
913.0
984.6
725.9
787.1
851.7
920.0
992.0
731.9
793.4
858.4
927.0
999.4
737.9
799.7
865.1
934.1
1007
743.9
806.1
871.8
941.2
1014
750.0
812.5
878.6
948.3
1022
756.1
819.0
885.4
955.5
1029
762.2
825.4
892.2
962.7
1037
768.4
832.0
899.1
970.0
1045
774.6
838.5
906.0
977.3
1052
60.80
64.30
67.90
71.60
75.40
6.50
6.60
6.70
1060*
1140
1223
1068
1148
1232
1076
1156
1241
1083
1164
1249
1091
1173
1258
1099
1181
1267
1107
1189
1276
1115
1198
1284
1123
1206
1293
1131
1215
1302
80.00
83.00
88.00
Figure 5. Example of expanded precision rating table.
48 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
Ratings that are defined with two or more segments (for
example, a rating defined with three equations that intersect at
specified breakpoints) should be considered as one rating and
only have one assigned number. In other words, the individual
equations that define that one rating should not have different
numbers.
A separate numbering sequence for each rating type
should be used for gaging stations that require two or more rat-
ings of different parameters. For instance, a velocity-index sta-
tion may have a stage-area rating, another rating of velocity
index and mean velocity, and a third rating of stage and velocity
factor. Each of these ratings should be numbered within their
own sequence of numbers, and consequently, in many cases
each of the three ratings would have the same number. The rat-
ings would be distinguished by rating type and rating number,
not only by number.
7.6 Updating and Renumbering Existing Rating Curves
Rating curves occasionally may require updating, or revi-
sion. Updates usually are composed of extrapolating either the
low end or the high end of the rating. If no change is made to the
available part of the rating, and it is simply extrapolated (either
end, or both ends), then the electronic processing system should
retain the rating with no change in the rating number. However,
the user should have the option to renumber the rating, if
desired. Revisions to an existing rating, or to a segment of an
existing rating, require renumbering, and revision of the period
of use. In effect, a new rating is established.
All updating and revisions of rating curves should be made
a part of the record processing notebook, as described in
section14.1. The date, users name, nature of the update, and
reason for updating should be required input to the log.
7.7 Rating Curve Plots
A graphical presentation of a rating curve is useful to the
user. Rating curves plotted on paper graphs traditionally have
been used for studying the relation between parameters (mainly
gage height and discharge), and very high standards have been
established for this purpose. For the relation between stage and
discharge, for instance, the hydraulics of the stream and control
are expressed in the rating curve plot. Therefore, the user can
make basic interpretations regarding the stream hydraulics if
the plot is made by observing specific guidelines. Details of
rating curve analysis and interpretation can be found in various
reports, and specifically by Rantz and others (1982), and by
Kennedy (1984).
Rating curves may be plotted either to linear scales or log-
arithmic scales. Certain types of ratings are better plotted with
linear scales, whereas other rating types are best plotted with
logarithmic scales. Preferences are frequently subjective, with
either type of plot as acceptable. The most frequently used
rating is the stage-discharge, and for hydraulic analysis pur-
poses the working plot should be done with logarithmic scales.
The electronic processing system should provide the capa-
bility to display more than one rating on the same plot. These
plots allows the user to compare ratings easily. Each rating dis-
played on a plot should be identified with rating number and
dates of application.
7.7.1 Reversal of Ordinate and Abscissa
A peculiarity of most rating curve plots is that the param-
eters plotted along the ordinate and abscissa scales are inter-
changed from the standard engineering practice. For rating
curves where gage height is the independent variable, gage
height always is plotted as the ordinate, and the dependent vari-
able as the abscissa. This designation allows gage height, which
is measured in a vertical direction, to be plotted in a vertical
direction. The rating curve slope for this method of plotting is
defined as a horizontal distance divided by a vertical distance.
The plotting scale preference for other ratings is given in table
13.
7.7.2 Electronic Processing System Monitor Plots
The electronic processing system should provide for plot-
ting of rating curves on the electronic processing system moni-
tor with interaction by the user to manipulate, draw, and define
ratings electronically. The requirements for electronic process-
ing system monitor plots are essentially the same as for paper
plots, as described in sections 7.7.3 through 7.7.8. These moni-
tor plots should be a highly flexible part of the electronic pro-
cessing system and also should provide the capability to pro-
duce a paper plot of the same rating, if required.
7.7.3 Paper Plots
The electronic processing system should be able to pro-
duce a paper plot of rating curves that are entered either through
the use of descriptor points or equations. Paper plots also should
be producible from system monitor plots. Requirements for
paper plots are described in sections 7.7.4 through 7.7.8.
7.7.4 Plotting Forms for Paper Plots
The electronic processing system should develop and print
the entire plotting form for a paper plot. It should print the grid
as well as the rating curve and other rating curve information.
Preprinted plotting forms are not advised. The combination
linear and log-log plotting form that traditionally has been used
for stage-discharge ratings (see fig. 6) should be included as a
paper plot option.
7.7.5 Linear Scale Plots
An arithmetically divided, linear, plotting scale is the sim-
plest type of rating curve plot. Linear scale plots are convenient
7. Rating Curves 49
to use and easy to read. Zero values can be plotted on the arith-
metic scale, whereas these values cannot be plotted on logarith-
mic scales. For this reason, linear scale plots frequently are used
for analyzing the low end of stage-discharge ratings. However,
for detailed hydraulic analysis linear scale plots have little or no
advantage over logarithmic scale plots. A stage-discharge rela-
tion plotted to a linear scale is almost always a curved line, con-
cave downward, which can be difficult to shape correctly if only
a few discharge measurements are available. Logarithmic scale
plots, on the other hand, have a number of analytical advantages
as described in section 7.7.6.
Linear scale plots are excellent for displaying a rating
curve. Usually, a rating curve is first drawn on a logarithmic
scale plot for shaping and analysis, then transferred to a linear
scale plot for display, (usually a paper plot). The electronic pro-
cessing system should make this process simple and easy.
7.7.5.1 Linear Scale Selection Procedure
Linear scale subdivisions should be established to cover
the complete range of the independent and dependent variables,
or a selected range. If only part of the rating is to be plotted, the
user should specify the range of either the independent variable
or the dependent variable for the desired plot. The electronic
processing system should make an initial determination of
scales, subdivided in uniform, even increments that are easy to
read and interpolate. The scales also should be chosen so that
the plotted rating curve is not very steep or very flat. Usually,
the curve should follow a slope of between 30 and 50 degrees.
The user should be able to change the scales easily and quickly
so that various plots can be viewed. The electronic processing
system should replot all measurements and rating curve infor-
mation each time a scale change is made.
7.7.5.2 Linear Scale Breaks
If the range of the variables is large, it may be necessary to
break the plotting scale and plot the rating curve in two or more
segments to provide scales that are easily read with the neces-
sary precision. This method may result in separate curves for
low water, medium water, and high water. Although two or
three separate curves are plotted, they should be plotted within
the same plotting form, if possible. The electronic processing
system should arrange the individual plots on the form so that
they are separate and distinct, properly scaled, and not overlap-
ping. Optionally, the separate curves could be plotted on sepa-
rate forms.
Figure 6. Linear and log-log combination plotting form.
50 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
7.7.6 Logarithmic Scale Plots
Many rating curves, and especially the relation between
gage height and discharge, can be analyzed best by plotting the
rating on logarithmic scale plots. Hydraulic characteristics that
are evident in logarithmic plots relate to the type of control, the
stream cross section, cross-section shape changes, and shifting
control patterns as described by Rantz and others (1982), and by
Kennedy (1984).
7.7.6.1 Logarithmic Scale Selection Procedure
The electronic processing system should plot rating curves
and rating curve information to logarithmic scales, by default, if
the rating is defined as a logarithmic rating. Ratings defined as
linear ratings, or equation ratings, may be plotted to logarithmic
scales at the users option. The initial plot should cover the full
range of the rating, or a selected range if defined. A normal log-
arithmic scale (no offset) always should be used for the
abscissa, or dependent variable. However, the ordinate scale
should be adjusted, by default, by an amount equal to the offset
defined for the primary rating being plotted. If multiple offsets
are defined with this rating, and the user chooses to plot a con-
tinuous rating for the complete range of all segments, then the
electronic processing system should default to the offset corre-
sponding to the lowest segment of the rating to make the initial
plot. If this is a plot for a new rating, where no other rating is to
be plotted, then the electronic processing system should define
the ordinate scale as a normal log scale (no offset), or use an
offset selected by the user. Although default scale selections
and offsets are prescribed, the user should be allowed to over-
ride the defaults and provide his/her own selections.
Generally, it is advised that full log cycles be used for log-
arithmic scale plots; however, the user should have the option
to set lower and/or upper limits so that only partial log cycles
are used at each end of the scales. The setting of scales should
be highly flexible and easily changed so the user can plot and
position the rating to the best advantage.
Logarithmic scale cycles always should be square. That is,
the linear measurement of a log cycle, both horizontally and
vertically, must be equal. Unless this requirement is met, it is
impossible to hydraulically analyze the resulting plot of the rat-
ing.
7.7.6.2 Scale Offsets
Many rating curves, and especially stage-discharge rating
curves, are analyzed and drawn on logarithmic scale plots,
using a scale offset for the ordinate, or gage-height scale. A
scale offset is a constant value that, when subtracted from the
independent variable (gage height), changes the plotting rela-
tion between the dependent and independent variables. The
results are a change to the curvature of the line of relation. If the
offset value is too large, the line will plot as a curve concave
downward. Conversely, if the offset value is too small, the
curve will plot concave upward. Theoretically, a segment of a
rating curve that is controlled by a specific cross section, or spe-
cific channel reach, only one scale offset will cause that seg-
ment of rating to plot as a straight line on a logarithmic scale
plot. This specific scale offset is referred to as the effective gage
height of zero flow for that specific segment of rating. For the
extreme low end segment of a stage-discharge relation, the
scale offset frequently will be equal to the true gage height of
zero flow. Defining the best scale offset for each segment of a
rating curve is a goal in rating curve analysis because it allows
the rating curve segment to be drawn as a straight line, which is
easier and usually more precise than drawing a curved line. The
electronic processing system should allow up to three scale off-
sets for each rating curve. This procedure conforms to many
stage-discharge rating curves, where three major segments are
present; (1) the extreme low water segment that usually is con-
trolled by a section control, (2) the within bank segment that can
be either a section control or channel control, and (3) the over-
bank segment that usually is channel control. Short transition
curves that join major rating segments usually are curved lines
that will not plot as a straight line, regardless of the scale offset.
7.7.6.2.1 Scale Offset Limitations
Scale offsets must be limited to values that are less than the
lowest value of the independent variable for the rating curve, or
segment of a curve, being defined. Otherwise, the mathematics
would produce zero or negative results, for which logarithms
cannot be determined. The electronic processing system should
not accept scale offsets that are equal to or greater than the
lowest value of the independent variable for the range in which
the offset applies.
Negative scale offsets are acceptable. A negative offset for
the low segment of a stage-discharge relation would indicate
that the gage height of zero flow is negative. Although such a
condition usually is not advised, this condition can result at
some gaging stations.
7.7.6.2.2 Determination of Best Scale Offset
When drawing a new rating curve, or rating curve seg-
ment, the best value for the scale offset is not always apparent.
A trial-and-error procedure usually is used, and therefore, the
electronic processing system should provide an easy method to
change the scale offset and quickly produce a new plot of the
measurements and rating curve. In this way, the user can work
with different scale offsets to find the one best suited for the
rating curve in question. Three or four trials usually are suffi-
cient to find the best offset, but the electronic processing system
should not limit the number of trials.
The electronic processing system should provide an option
to compute a scale offset. The computation method is one
defined by Johnson (1952), and is further described by Kennedy
(1984) and Rantz and others (1982). The following computation
steps are required for the procedure.
1. Choose two points on the rating curve segment for which a
computation of the scale offset, e, is desired. One of the
chosen points should be near the lower end of the segment,
7. Rating Curves 51
and one point should be near the upper end of the segment.
The two point coordinates are G
1
, Q
1
, and G
2
, Q
2
.
2. Compute a value, Q
3
, based on Q
1
and Q
2
, and the
equation
(22)
3. Determine a value, G
3
, from the rating curve that
corresponds to Q
3
.
4. Compute the value, e, based on the equation
. (23)
5. Round the resulting value of the scale offset, e, to one that
easily is used for the logarithmic plot.
7.7.6.3 Rating Curve Shaping
Stage-discharge rating curves usually are shaped by fitting
a curve or straight line to a series of plotted discharge measure-
ments. For paper plots, this fitting is easily performed by hand
with straight edges and preformed plastic curves. For electronic
processing system monitor plots, a method, or methods, should
be provided whereby the user similarly can fit a smooth curve
or straight line to points plotted on the electronic processing
system monitor. This should be a highly interactive process
between the electronic processing system and the user.
Certain helps should be made available for electronic pro-
cessing system plots to ensure that stage-discharge ratings are
hydraulically correct. One such help is to plot a theoretical
rating based on the control properties and the governing hydrau-
lic equations. The computations and plotting of theoretical rat-
ings should be performed with the electronic processing system,
but will require interaction with the user. Methods of computing
theoretical ratings will be described in more detail in section
7.8. The theoretical ratings are used primarily for defining the
rating shape, and not necessarily for locating the rating position.
The user must use such ratings with caution, and should make
discharge measurements to verify these ratings whenever possi-
ble.
Another help, when working with logarithmic scale ratings
for stage-discharge stations, is to measure the slope of straight
line rating segments for comparison to theoretical slopes that
correspond to various control conditions. Rating slope compu-
tations should be done automatically with the electronic pro-
cessing system on command. The user first should designate the
end points of the segment of rating where slope is to measured.
The electronic processing system should check to be sure the
selected rating curve segment is reasonably close to a straight-
line segment. This checking can be done by computing percent-
age differences of discharge between the actual rating and the
straight line defined by the selected end points, at intermediate
points along the rating segment. If any difference exceeds + or
- 1 percent (default value), the rating segment should be consid-
ered curvilinear and the slope should not be computed. The
electronic processing system should issue a statement to the
user to this effect, and simultaneously provide an opportunity
for the user to select a different percentage to use for checking
the differences, or to select a different rating segment to check.
On the other hand, if the rating segment is found to be a straight
line (within the default, or selected, percentage difference), then
the slope should be computed and displayed. When displaying
a computed slope, the electronic processing system also should
include the statement “section control” for slopes greater than
2.0, and “channel control” for slopes less than 2.0.
The slope of a logarithmic rating is computed as the run
(horizontal distance) divided by the rise (vertical distance). The
run and rise are measured as linear distances on logarithmic
plotting scales. They should not be measured in terms of the
independent and dependent variables, but rather in terms of the
logarithms of these variables. For a straight-line segment, two
points [(Q
1
, G
1
) and (Q
2
, G
2
)] on the segment can be used to
compute the slope using
, (24)
where
c = the rating curve slope, and
e = the scale offset for the independent variable.
7.7.7 Mathematical Fitting of Rating Curves
As previously stated, rating curves are hydraulic functions
that should conform to the laws of hydraulics. For this reason,
rating curves should not be defined with statistical methods,
such as regression techniques, or by fitting curves with mathe-
matical methods such as quadratic equations. All measurements
used in a mathematical or statistical derivation are assumed to
lie on the same rating curve. Frequently, this is an incorrect
assumption, especially for streams with shifting controls.
7.7.8 Measurement Plotting
Selected field measurements and other computed parame-
ters should be plotted with the electronic processing system on
rating curve plots. The rating type will govern the parameters to
be plotted. For each respective rating, these may be measure-
ments of stage and discharge, stage and fall, index velocity and
mean velocity, stage and area, or elevation and reservoir con-
tents. Computed parameters such as discharge ratio and fall
ratio for slope ratings, velocity factor and stage for index veloc-
ity ratings, and 1/US
c
and stage for change-in-stage ratings also
should be plotted as required.
7.7.8.1 Selection of Measurements
The user should have considerable flexibility in the selec-
tion of measurements and computed parameters to be plotted.
The selection criteria should be based on measurement number,
measurement date, independent variable, dependent variable,
Q
3
Q
1
Q
2
=
e
G
1
G
2
G
3
2
–
G
1
G
2
2G
3
–+
-----------------------------------=
c
Qlog
2
Q
1
log–
Y
2
e–()log Y
1
e–()log–
------------------------------------------------------------=
52 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
and measurement type (for example, ice measurement, control
condition, and others). Various combinations of the selection
parameters also should be permitted; however, the electronic
processing system should not allow unlimited selection of all
possible combinations. Unlimited selection could lead to con-
flicting and sometimes biased plotting standards. Various selec-
tion criteria are given below.
1. Plot all measurements with numbers greater than a speci-
fied number, less than a specified number, and (or) between
two specified numbers.
2. Plot all measurements with dates subsequent to a specified
date, prior to a specified date, and (or) between two
specified dates.
3. Plot all measurements where the independent variable
exceeds a specified value, is less than a specified value, or
between two specified values.
4. Plot all measurements where the dependent variable
exceeds a specified value, is less than a specified value, or
between two specified values.
Plot combinations of the above selection criteria as fol-
lows:
1. Combinations of (1) and (3).
2. Combinations of (1) and (4).
3. Combinations of (2) and (3).
4. Combinations of (2) and (4).
Other combinations of plotting criteria are not recom-
mended.
For each of the above selection criteria and combinations,
the user should be allowed to select various types of measure-
ments, namely selected control conditions and measurement
method.
7.7.8.2 Selection of Independent Variable
Gage height is used as the independent variable for most of
the rating curve types, such as gage height and discharge, or
gage height and area. For these rating types, the selection of
inside or outside gage height becomes an important consider-
ation for rating curve plots. It is common practice that both an
inside gage reading and an outside gage reading will be mea-
sured. Frequently, these readings are identical, and either gage
height can be used. However, the inside and outside gages do
not read the same at some stations, sometimes by small amounts
of only .01 or .02 ft, but in other cases where drawdown is
present the difference could be large.
The electronic processing system should, by default, select
the inside gage height for those ratings that use gage height as
the independent variable. The user should have the option to
change the default to outside gage height, if desired. Rating
curve plots clearly should label the gage-height scale as “Inside
Gage Height” or “Outside Gage Height,” whichever is applica-
ble.
The electronic processing system should not allow a mix-
ture of inside and outside gage heights to be plotted on the same
rating curve plot. Such a practice could lead to confusion and
improper rating analysis.
Only two rating types use independent variables other than
gage height (or elevation). For velocity stations, the rating of
index velocity and mean velocity uses the mean index velocity
during the period of time of the discharge measurement. For
slope stations, the rating of fall ratio and discharge ratio uses the
computed value of the fall ratio at the time of the discharge mea-
surement as the independent variable.
7.7.8.3 Selection of Dependent Variable
The dependent variable is selected according to the type of
rating being plotted, as indicated in table 13. The dependent
variable for each rating type is given below.
• Stage-discharge rating—Discharge is the dependent
variable and should be plotted for all discharge mea-
surements. For discharge measurements where a mea-
sured discharge and an adjusted discharge are entered
in the discharge measurement file, they both should be
plotted, but with different symbols. A connecting line
between the measured discharge and the adjusted dis-
charge, as indicated below, should be shown on the
rating to indicate that the two discharges are for the
same measurement.
• Stage-area rating—The area measured at the standard
cross section is the dependent variable.
• Index velocity-mean velocity rating—The mean veloc-
ity in the standard cross section at the time of the dis-
charge measurement is the dependent variable.
• Stage-velocity factor rating—The mean velocity
adjustment factor is the dependent variable.
• Stage-fall rating—The mean fall between the base gage
and the auxiliary gage at the time of the discharge mea-
surement is the dependent variable.
•Fall ratio-discharge ratio rating—The computed dis-
charge ratio, Q
m
/Q
r
, at the time of the discharge mea-
surement is the dependent variable.
• Stage-1/USc rating—The flood wave factor, 1/US
c
, is
the dependent variable.
• Elevation-contents rating—The reservoir contents is
the dependent variable.
Connecting line
Measured
discharge
Adjusted
discharge
7. Rating Curves 53
7.7.8.4 Identification of Measurements on Rating-Curve Plots
Each measurement plotted on a rating curve should be
identified by measurement number. The identification method
should conform to the traditional USGS method used for paper
plots, where the measurement point is shown as a small circle,
a 45 degree line, 1-in long, is drawn from the measurement
point, and the measurement number is shown at the end of the
line. For some discharge measurements, an optional feature
should allow the user to show the rate of change in stage, in feet
per hour, on the measurement line. The following sketch illus-
trates these concepts.
7.7.8.5 Other Rating-Curve Plot Information
The rating curve plot should include information that iden-
tifies the gaging station by number and name, the rating type,
the period of use for each rating plotted, the selection criteria of
the plotted measurements, the date of rating development and
approval for each plotted rating, the name of the user responsi-
ble for developing each plotted rating, and the name of the
person approving each rating. Each rating shown on the plot
should be clearly identified by rating number. Scales should be
labeled with the correct parameter name, and the units of mea-
surement for the parameter.
The rating plot sheet should contain a disclaimer statement
that alerts the user that direct application of the rating may lead
to errors if undefined shifts and/or backwater occur. The word-
ing of the disclaimer statement should be designed to fit the spe-
cific gaging station and the type of rating. A typical statement
for a stage-discharge rating is
“This rating curve is applicable only for stream con-
ditions unaffected by backwater, ice, debris, scour,
and other undefined changes to the control.”
7.8 Rating Curve Development Procedures
Rating curves traditionally have been developed by hand
plotting of measurements and manually drawing curves of best
fit. Complex ratings, such as slope ratings and velocity-index
ratings, have been developed through a combination of hand
calculations and plotting methods. All of these methods are
time-consuming and tedious. The computer development meth-
ods that can assist the user in rating curve shaping and definition
are given in Sections 7.8.1 through 7.8.4.
7.8.1 Stage-Discharge Ratings
Stage-discharge ratings are graphical relations between
stream stage and stream discharge. These ratings can be devel-
oped within the electronic processing system using the plotting
and curve drawing functions described in section 7.7. However,
the user should use care in ensuring that the ratings are hydrau-
lically correct. The electronic processing system can be used in
providing computations that aid in the correct hydraulic shaping
of the rating curves. Three such methods, section control, chan-
nel control, and step-backwater, are described in sections
7.8.1.1 through 7.8.1.3.
7.8.1.1 Section Control Methods
Rating segments that are controlled by a specific cross sec-
tion of the stream, such as a sand bar, rock outcropping, man-
made weir, or other stream feature, can be approximated by
flow computations based on a surveyed cross section of the con-
trol and the weir equation. The input of cross-section data and
the computation of cross-section properties are given in Section
6.4.
Flow computations can be made for the section control by
using the cross-section properties, a coefficient of discharge, C,
and the weir equation. For purposes of defining the theoretical
rating shape (not exact rating position), the method defined here
is simplified and some of the more detailed intricacies of weir
computations are not accounted for in the method.
The general form for the weir equation to be used for sec-
tion control computations is as follows:
, (25)
where
Q = discharge, in cubic feet per second,
C = the discharge coefficient,
L = the top width, in feet, of the water surface at the con-
trol section and for the gage height of interest, and
h = the head, in feet, (difference between the gage height
and lowest point of the control section).
The discharge coefficient, C, used in the weir equation
may be input directly by the user at the time the cross-section
data are entered. A value of C should be required for the lower
limit of gage height for the computations and for the upper limit
of computations. Optionally, C- values may be specified for
intermediate gage heights. The electronic processing system
should use linear interpolation, based on gage height, for inter-
mediate values of C.
For control sections where C is not known, the user may
choose to obtain estimates of the C values computed from dis-
charge measurement data. The electronic processing system
should allow the user to designate specific discharge measure-
ments for which a C value would be computed, based on the
gage height and discharge of the measurement, the cross sec-
tion, and the weir equation. The computation of C would be
based on the weir equation
-0.04
123
Q CLh
1.5
=
54 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
(26)
The electronic processing system should display the com-
puted values of C in tabular format for each of the discharge
measurements. The user can use this information to choose
values of C to input as described above. The electronic process-
ing system should allow the user the option to plot gage height
and C, and draw a smooth curve of relation. This curve could be
used for defining C for the range of theoretical rating curve
computations.
The range of theoretical computations for a given cross
section should be specified by defining the lower and upper
limit gage height. Intermediate computations should be spaced
at 0.1 intervals of gage height. The theoretical rating curve
should be plotted on the rating curve plot, and clearly identified
as theoretical.
7.8.1.2 Channel Control Methods
Rating curve segments that are controlled by channel con-
ditions such as cross-section area, channel slope, channel shape,
and roughness of the bed and banks, can be defined by theoret-
ical computations using the Manning equation and a typical
cross section near the gage. Such computations can define the
correct hydraulic shape of the rating, but not necessarily the cor-
rect position of the rating. Computations of this type have been
historically referred to as the conveyance-slope method as
described by Rantz and others (1982).
The Manning equation is
, (27)
where
Q = discharge, in cubic feet per second,
n = the Manning roughness coefficient,
A = the cross-section area, in square feet,
R = the hydraulic radius, in feet, computed as the area, A,
divided by the wetted perimeter of the cross section,
and
S = the energy slope, in feet/feet.
The first part of the equation, consisting of the n, A, and R
terms, commonly is referred to as channel conveyance, K, and
can be computed from the channel cross section and visual esti-
mates of the roughness coefficient, n. The equation for convey-
ance, K, is
. (28)
Some cross sections may be subdivided into two or more
subsections because of channel shape and (or) roughness vari-
ability. For such cross sections, the conveyance, K, should be
computed for each subsection, and a total conveyance, K deter-
mined as a summation of the individual subsection K’s. Points
of subdivision are defined at the time the channel cross-section
data are entered.
The energy slope, S, can be estimated from various sources
such as topographic maps and highwater marks. It also can be
computed from the Manning equation, the surveyed cross sec-
tion, and discharge measurements. The equation for computing
slope, when the discharge is known, is
(29)
The electronic processing system should allow the user to
designate specific discharge measurements for which slope, S,
is computed. These computed values of S should be displayed
in tabular format, from which the user can choose values to
input at the lower and upper limits of the conveyance-slope
computations. The electronic processing system should use
linear interpolation to determine intermediate values of slope.
The electronic processing system should provide an option
for the user to plot the computed values of slope and gage height
so that a curve of relation can be drawn. This curve then would
be used to determine values of S for the conveyance-slope com-
putations.
The range of theoretical computations for a given cross
section using the conveyance-slope method should be specified
by defining the lower and upper limit gage height. Intermediate
computations should be spaced at 0.5 ft intervals of gage height,
by default. The user should be allowed to specify other intervals
if desired. The theoretical rating curve should be plotted on the
rating curve plot, and clearly identified as theoretical.
7.8.1.3 Step-Backwater Method
Step-backwater is a water-surface profile computation
method that requires a minimum of two cross sections, but gen-
erally four or more cross sections are required to produce accu-
rate results. The details of the method are described by Shear-
man (1990) and will not be discussed in this report. It is an
excellent method to define the shape, and position of the rating
curve, and sometimes is used instead of discharge measure-
ments when they are difficult to obtain. Cross-section data and
other information necessary for step-backwater computation
are entered in the step-backwater program.
The step-backwater method computes water-surface ele-
vations at each cross section in the stream reach downstream
from the gage. The computation depends on a given discharge
in the reach and on an assumed water-surface elevation at the
downstream end of the reach. Two or more downstream eleva-
tions are used to verify that the results at the gage will define a
unique stage-discharge relation. The electronic processing
system should provide an option to plot the profiles of water-
surface elevations for the various starting elevations for each
selected discharge. This type of plot is referred to as a conver-
gence plot that is useful in evaluating the accuracy of the step-
backwater results.
The electronic processing system should have a direct link
to the step-backwater software so that results can be transferred
easily to the rating analysis for a gaging station. Generally, a
series of discharges is selected and for each discharge in the
C
Q
Lh
1.5
------------=
Q
1.486
n
-------------
AR
23⁄
S
12⁄
=
K
1.486
n
-------------
AR
23⁄
=
SQK⁄[]
2
=
8. Shift Adjustments 55
series the step-backwater method will compute a gage height at
each cross section used in the computations. The parameters
that are required to be transferred are the discharges and the cor-
responding computed gage heights for the cross section at the
gage. Each transferred pair (gage height at the gage and corre-
sponding discharge) should be plotted on the rating curve and
identified as a step-backwater computation.
The step-backwater program also computes the water-sur-
face elevation for critical depth of flow for each discharge at
each cross section. The user should have the option to select a
cross section and plot the critical water-surface elevation (gage
height) computed for that section, and the corresponding dis-
charge on the rating plot. This is an additional method to define
the shape of a rating where section control is effective.
7.8.2 Slope Ratings
Slope ratings are used for stations with channel controls
where variable stream slope downstream from the base gage
affects the position of the stage-discharge relation. Variable
stream slope usually is caused by a downstream condition, such
as a reservoir, tributary stream, or overbank storage. In reality,
the term “slope rating” is a misnomer, because these ratings do
not use actual stream slope as a rating parameter. Instead, an
index of stream slope is used, which usually is the water-surface
fall measured between the base gage and an auxiliary gage
downstream from the base gage. For some slope stations, the
auxiliary gage may be located upstream from the base gage, but
a better index of stream slope can be obtained if the auxiliary
gage is located downstream from the base gage.
The rating method for slope stations involves a complex
relation of three separate rating curves, (1) stage-discharge, (2)
stage-fall, and (3) fall ratio-discharge ratio. These ratings are
described in section 7.1, and a detailed description of slope rat-
ings can be found in Kennedy (1984) and Rantz and others
(1982). Slope ratings usually are classified into three specific
types: (1) unit fall ratings, (2) constant fall ratings, and (3) lim-
iting fall ratings. Although these different fall ratings are treated
separately in the literature, they can be treated as one rating for
computational purposes. This treatment is accomplished by
defining the stage-fall rating to fit the specific fall rating type.
For instance, if a unit fall rating is desired, then the fall rating is
defined so that fall equals 1 ft for all gage heights. If a constant
fall rating is desired, for a fall other than unity, then the fall
rating is defined so that the desired constant fall is computed for
all gage heights. Finally, if a limiting fall rating is desired, then
the stage-fall rating is defined so that a variable fall is com-
puted, which is dependent on gage height.
The development of slope ratings must be defined empiri-
cally, using discharge measurements, simultaneous measure-
ments of fall, and a trial-and-error method to position and shape
the individual rating curves. This procedure traditionally has
been done by hand plotting and hand computing methods, a
slow and tedious process. The electronic processing system
should provide an interactive process, whereby the user makes
the decisions regarding the curve positions and shape, and the
system makes the routine computations and plots.
7.8.3 Index Velocity Ratings
Index velocity ratings, like slope ratings, can be used for
gaging stations where variable backwater precludes the use of a
stage-discharge rating. For index velocity stations, some
method of recording a point or line velocity is required. This
recording normally is accomplished with separate gages, such
as vane gages, electromagnetic gages, or acoustic gages.
A stage-discharge rating is not used at gaging stations
where index-velocity ratings are used. Instead, ratings are
developed for index velocity and mean stream velocity, gage
height and cross-section area, and gage height and velocity
factor (optional). Each of these ratings are developed for a stan-
dard cross section of the stream. Development of the ratings is
fairly straight forward, but may require some amount of trial-
and -error fitting, especially if the stage and velocity-factor
rating is used. The electronic processing system should provide
an interactive process that allows the user to fit and test the rat-
ings so that the best combination of ratings can be attained.
The methods described here for index velocity ratings
refer to a single channel rating situation. However, these meth-
ods can be used where the stream is subdivided into two or more
subsections, either horizontally or vertically. In such cases, each
subsection has its own set of ratings, and is computed sepa-
rately. The total discharge is the sum of the subsection dis-
charges.
7.8.4 Rate-of-Change-in-Stage Ratings
Rate-of-change-in-stage ratings sometimes are used at
gaging stations where changing discharge causes a variable
stream slope. These ratings are used for stations with a condi-
tion frequently referred to as loop ratings. The Boyer method in
Water Supply Paper 2175 (Rantz and others, 1982) usually is
used to determine the rating at a station with this condition. This
method requires two ratings: (1) a stage-discharge rating, and
(2) a stage-1/US
c
rating. An empirical, trial-and-error method,
is used to develop these ratings, and requires a number of dis-
charge measurements. Like other complex ratings, this rating
traditionally has been done using hand computations and hand-
plotting methods. The electronic processing system should pro-
vide an interactive method so the user can quickly and easily
develop a Boyer rating. The user should be allowed to fit and
test trial ratings until the best combination is attained.
8. Shift Adjustments
Shifts are gage-height adjustments used to account for
temporary changes to rating curves, without having to re-define
the rating curve. The method for computing shift information
56 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
for the various types of discharge measurements is described in
Section 6.1.4, Shift Analysis. For surface-water computations,
shift adjustments are added to unit values of the input parameter
to yield temporary unit values that are applied to the rating
curve for computation of the output dependent variable. The
algebraic sign of the shift must be maintained correctly, as
defined in section 6.1.4. When measurements plot above a
rating curve, that is, when the actual gage height for a given dis-
charge is higher than indicated by the rating curve, the sign of
the shift is negative. When measurements plot below a rating
curve, the sign of the shift is positive. Also, it is important to
note that a shift is a temporary correction, used only for compu-
tational purposes. It does not permanently alter the input unit
value.
Although most shifts will apply to stage-discharge ratings,
they also may be defined and applied to the index velocity and
mean velocity rating for index-velocity stations. Shifts should
not be allowed for any other types of rating curves except stage-
discharge ratings and index velocity and mean velocity ratings.
Because shifts are predominantly used for stage-discharge rat-
ings, the shift discussions in this section will relate to that type
of rating.
Shifts usually are applied only when discharge measure-
ments deviate from a rating curve by more than a specified per-
centage. The specified percentage frequently is based on the
accuracy of discharge measurements that can be made at the
gaging station. For instance, if discharge measurements can be
made with 5 percent or better accuracy, then shifts will be used
only when measurements deviate more than 5 percent from the
rating. Otherwise, if more than 2 or 3 consecutive discharge
measurements consistently plot on one side of the rating a shift
curve may be used for these measurements even though they are
within the specified shift percentage. See the following section
(Shift Curves) for methods for defining shift curves.
8.1 Shift Curves
Shift-variation diagrams (a plot of gage height and shift,
and commonly known as V-diagrams) that have been used in
previous computing systems, such as in the Water Data Storage
and Retrieval System, WATSTORE, (Hutchinson and others,
1977), or the Automated Data Processing System, ADAPS,
(Dempster, 1990), should not be considered the primary method
of defining and applying shifts. Shift curves, as defined here,
become the primary method of defining and applying shifts.
Shift-variation diagrams and tables are not eliminated from the
system, but used more for an evaluative tool as described in sub-
sequent sections.
A shift curve is defined as a shifted-rating curve, and has
all of the basic characteristics of a rating curve. A few common
characteristics of shift curves are
• Shift curves have the same independent and dependent
variables as the parent rating curve.The parent rating
curve is defined as the original, primary rating curve
that is being shifted.
• Shift curves should have the same basic shape as the
parent rating curve.
• The algebraic difference between independent vari-
ables of a parent rating curve and a shift curve, for any
given dependent variable, is defined as the shift that
applies to the independent variable of the shift curve.
For application purposes, shift curves should be trans-
lated with the electronic processing system into tempo-
rary adjustments (shifts) of unit values of gage height
used to compute unit values of discharge.
• Shift curves defined for a given control segment (for
example, section control) of the rating usually apply
only to that segment of the rating. For example, a shift
curve defined for a low-water section control should be
merged with the parent rating at or near the transition to
a channel control segment of the rating, unless dis-
charge measurements or other information show other-
wise.
• Shift curves may be time-interpolated as described in
section 8.4.4.
8.1.1 Input of Shift Curves
Shift curves should be an integral part of rating curves, and
may be defined graphically or by tabular input, using as a guide,
a screen displayed plot of the current rating curve, the last used
shift curve, and selected discharge measurements. The elec-
tronic processing system should allow the user to draw and
shape a shift curve on the screen in a similar manner to drawing
and shaping rating curves on the screen. The current, or parent,
rating curve should be displayed, by default, at the time shift
curves are defined. However, the user should be allowed to dis-
play any other defined rating curve or previously used shift
curves, simultaneously or individually.
8.1.2 Shift Curve Tables and Diagrams
For each shift curve defined graphically, a summary table
of the independent variable (usually gage height) and corre-
sponding shift should be produced automatically with the elec-
tronic processing system. The user may choose to enter shifts in
the table prior to defining a shift curve graphically. Therefore,
the tabular entries automatically should be displayed as a shift
curve on the rating plot. This table will aid the user in defining
and smoothing the shift curve. The table should begin with the
lowest gage height of the shift curve and end with the highest
gage height of the shift curve. The tabular listing should include
all points along the shift curve that were specified by the user
during the process of defining the shift curve.
A plot of gage height and shift, or shift-variation diagram,
for all points in the shift curve table should be an option. This
diagram should not be considered the basic method of defining
a shift curve, but it can be useful in evaluating the shift defini-
tions and applications.
8. Shift Adjustments 57
The shift curve table and diagram should be displayed
simultaneously with the shift and rating curve plot. The table
and diagram should be linked directly to the shift curve plot, so
that a graphical change made to the plotted curve automatically
would be reflected in the table and diagram. Likewise, a change
made in the table automatically should be reflected in the plot-
ted curve. A typical shift curve plot, shift diagram, and shift
curve table are illustrated in figure 7.
Figure 7. Typical rating curve, shift curve, shift table, and option-
al shift diagram.
8.1.3 Period of Use for Shift Curves
Each shift curve must be given a starting date and time. An
ending date and time may or may not be required, depending on
how the shift curve is to be applied. When both starting and
ending dates, and times are given for a specific shift curve, then
that shift curve will be applied directly throughout the defined
period of time.
If an ending date and time for a specified shift curve is not
given, then that shift curve will be time-interpolated to the suc-
ceeding shift curve, if one is given. If a succeeding shift curve
is not given, then the last specified shift curve will be used
directly until it is terminated either with an ending date and
time, or with a succeeding shift curve. Additional details on
time-interpolation of shift curves are given in section 8.4.
8.1.4 Extrapolation of Shift Curves
Shift curves should be extrapolated parallel to the parent
rating curve below their lowest defined gage height and above
their highest defined gage height. For example, if the shift curve
is 0.20 ft above the parent rating curve at the highest defined
gage height of the shift curve, then a constant shift of 0.20 ft
should be used for all gage heights greater than the highest
defined gage height of the shift curve. Likewise, a shift equal to
the shift for the lowest defined gage height should be used for
all gage heights below the lowest defined gage height. The elec-
tronic processing system automatically should make these
extrapolations when they are needed for computing a discharge
record. It should distinguish the extrapolated part of a shift
curve on the shift curve plot with a dashed line.
8.2 Shift Curve Numbering
Each defined shift curve should be numbered automati-
cally with the electronic processing system. Numbers should be
referenced to the rating curve for which the shift curve applies.
A two part number is recommended, with the first part being the
rating curve number, and the second part a sequential shift
curve number that is determined in the order that the shifts
curves are defined. Shift curves should retain its number once
assigned, and not be renumbered. The two parts of the shift
curve number should be separated by a colon (:). Following are
two examples of shift curve numbers.
1. The second shift curve defined for rating number 5 would
be numbered 5:0002.
2. The third shift curve defined for rating number 12b.2
would be numbered 12b.2:0003.
8.3 Shift Curve Error Analysis
An error analysis should be performed with the electronic
processing system for each discharge measurement to show the
effects of shifting or not shifting. In effect, this analysis is an
extension of the computations described in section 6.1.4 (Shift
Analysis). The error analysis should show the optimum shift
and the percent difference of the discharge measurement with-
out shifting, as described in section 6.1.4. Also, the analysis
should show the percent difference between the measured dis-
charge and the discharge computed by using the optimum shift.
In addition, it should show the shift actually applied at the exact
date and time of the discharge measurement based on the
defined shift curve and the interpolation method, if used. It also
should show the percent difference between the measured dis-
charge and the discharge computed on the basis of the applied
shift. The shift analysis also should show the range of uncer-
tainty for each discharge measurement, based on the assigned
accuracy of the measurements. This range of uncertainty is
referred to as the uncertainty bars for a measurement.
The electronic processing system should produce a table of
discharge measurements showing the results of the error analy-
sis and identifying information about each discharge measure-
ment, such as measurement number, date, gage height, mea-
sured discharge, and measurement accuracy. The table
normally should cover the period of time for a water year
1
, and
Shift
Diagram
Shift
Shift Curve 5:0003
Rating No. 5
Summary Shift Table for Shift Curve 5:0003
Stage Shift
x.xx x.xx
x.xx x.xx
x.xx x.xx
x.xx x.xx
x.xx x.xx
Log of
Gage Height
Log of Discharge
(-) 0 (+)
1
The water year is the period of time from October 1 through the following September 30.
58 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
Measurement
Rating Shift Analysis Uncertainty Bars
Applied Shift
Optimum Shift Without Shift Low
Optimum
Shift
High
Number Date Stage Discharge RTD
PCT
UNC
(+/-)
Shift Discharge % Diff Discharge % Diff Shift Discharge Shift Discharge Shift Discharge % Diff
213 09/15/1992 2.18 115.0 P 10.0 -0.03 116.1 -0.9 123.3 -6.7 -0.08 103.5 -0.03 0.01 126.5 -0.02 118.1 -2.6
214 10/01/1992 2.40 178.0 F 8.0 -0.01 177.5 0.3 180.2 -1.2 -0.06 163.8 -0.01 0.04 192.2 -0.01 177.5 0.3
215 11/02/1992 1.91 60.40 F 8.0 -0.03 60.94 -0.9 65.84 -8.3 -0.06 55.57 -0.03 0.00 65.23 -0.01 63.80 3.1
216 03/23/1993 1.63 24.60 F 8.0 -0.01 25.10 -2.0 26.15 -5.9 -0.03 22.63 -0.01 0.00 26.57 -0.01 25.10 -2.09
217 04/29/1993 2.08 93.50 F 8.0 -0.03 92.95 0.6 99.72 -6.2 -0.06 86.02 -0.03 0.01 101.0 -0.02 95.10 -1.7
218 05/18/1993 3.58 563.0 F 8.0 -0.04 561.2 0.3 576.7 -2.4 -0.15 518.0 -0.04 0.08 608.0 -0.04 561.2 0.3
219 06/29/1993 2.79 276.0 F 8.0 -0.06 276.9 -0.3 295.8 -6.7 -0.13 253.9 -0.06 0.01 298.1 -0.04 283.1 -2.5
220 08/11/1993 2.09 99.80 F 8.0 -0.01 99.72 0.1 102.0 -2.2 -0.05 91.82 -0.01 0.03 107.8 -0.01 99.72 0.1
221 10/22/1993 1.78 44.40 F 8.0 -0.01 44.24 0.4 45.79 -3.0 -0.03 40.85 -0.01 0.01 47.95 -0.01 44.24 0.4
include the last measurement of the previous water year, and the
first measurement of the subsequent water year. It also can
cover a period of time defined by the user. An example of a
table of this type is shown in figure 8.
8.4 Shift Curve Application
Shifts are applied to all unit values of gage height (or other
input parameter) on the basis of defined shift curves, as
described in sections 8.4.1 through 8.4.4. These methods can be
used for constant shifts, time interpolation of shifts, stage inter-
polation, and a combination of time and stage interpolation.
8.4.1 Individual Shift Curves
An individual shift curve can be used when it is desired to
apply a constant shift, or a shift varied with stage for a period of
time without varying the shift curve. The individual shift curve
can be applied to a specified period of time by defining the start-
ing date and time, and the ending date and time. If an ending
date and time are not defined, then the shift curve will be used
indefinitely until such time as an ending date and time are
defined.
A constant shift that does not vary with stage or time can
be accomplished by defining an individual shift curve with a
single point. When a single point on a shift curve is used to
define that shift curve, the shift will automatically be extrapo-
lated below and above the specified gage height using the same
shift entered for the specified gage height. This sometimes is
referred to as a shift curve parallel to the rating curve. It is con-
sidered parallel because the shift is constant throughout the
range of application.
An individual shift curve also can be used to apply shifts
that are varied by stage only (not varied by time). This method
defines an individual shift curve drawn so that it will have dif-
ferent shifts at different gage heights. This is a shift curve that
is not parallel to the rating curve.
8.4.2 Multiple Shift Curves
Two or more shift curves can be used in combination to
apply shifts to unit values so that the shifts are varied either by
time only, or by both stage and time. Varying the shift in this
way is accomplished by defining a shift curve and assigning it
a starting date and time, but no ending date and time. A second
shift curve is defined with a subsequent starting date and time.
If the two shift curves are defined so that each one has a differ-
ent constant shift (not varied with stage), then the electronic
processing system will interpolate between these two shifts
based on time only. This procedure commonly is referred to as
time interpolation of shifts.
If two consecutive shift curves are entered so that one or
both of them have shifts that vary by stage, then the electronic
processing system will interpolate shifts based on both stage
and time for all unit values between the two assigned shift
curves. The interpolation method is described in section 8.4.4.
Two or more consecutive shift curves entered with starting
dates and times only (no ending dates and times) will be inter-
polated for intermediate dates and times. In this manner, the
user can vary shifts by stage and time, or time only, from one
shift curve to another, and even between a shift curve and the
base rating.
8.4.3 Additive Shift Curves
The electronic processing system should not allow two or
more shift curves to be added. If overlapping dates and times are
entered for two shift curves, the electronic processing system
should issue a warning message to this effect, and require that
corrections be made.
Figure 8. Example of shift-analysis table [RTD, measurement rating; P, poor; F, fair; G, good; E, excellent; PCT UNC, percent uncertainty;
%DIFF, percent difference].
9. Primary Computations 59
8.4.4 Shift Interpolation Procedure
Shift curves are defined and numbered as a means of
describing and tracking specific shifting characteristics at spe-
cific points in time. Each shift curve usually is based on one or
more discharge measurement and other field observations that
define a change in the position of the rating curve, and this
change usually is considered a temporary change. To estimate
shifts at other times, intermediate to the defined shift curves, a
linear-interpolation procedure is used.
Individual shifts, and not entire shift curves, should be
interpolated. That is, only those shifts needed to adjust unit
values should be determined by interpolation, and not those out-
side the range of recorded unit values. Likewise, the interpola-
tion process should be continuous in time, so that a shift inter-
polation is performed for each unit value to which shifts are to
be applied.
The interpolation procedure is described in the following
step-by-step example.
1. Two shift curves, 001 and 002, are defined graphically for
use at dates and times, t
1
and t
2
, respectively.
2. An interpolated shift, S
n
, is required for unit value, G
n
, at
an intermediate date and time, t
n
.
3. The electronic processing system computes the shifts, S
1
and S
2
, corresponding to the unit value, G
n
, from each of
the shift curves, 001 and 002, respectively.
4. The electronic processing system performs an unweighted,
linear time interpolation of shifts S
1
at time t
1
, and S
2
at
time t
2
, to obtain the shift, S
n
, at time t
n
.
5. The same interpolation procedure is used to estimate shifts
for all other unit values resulting between times, t
1
and t
2
.
8.4.5 Rounding and Significant Figures
All computed shifts and interpolated shifts should be
rounded to two significant figures to the right of the decimal
(for example, all shifts should be rounded to hundredths).
Rounding should be performed before any application process.
8.4.6 Unit Value Graphical Comparisons of Shifts
Shifts that are applied to a time series of unit values should
be displayed with the electronic processing system in a graphi-
cal plot. The graphical comparison should show a time-series
plot of the unit values of gage height (or other independent vari-
able) and a superimposed plot of the unit values of shifts. Scales
for the two plots should be used so that each plot is easily dis-
cernible and readable. The user should have the option to
change either or both of the scales. An example plot is shown in
figure 9.
8.4.7 Shift Curve Tracking Procedure
The electronic processing system should summarize each
shift curve that was used for computing discharge records for a
water year. This provides a record of shifting instructions, and
it should be presented in tabular format so that the user can
easily review all shift curves in chronological order. A new
record of shifting should be started at the beginning of each
water year, and it should include the last shift curve used in the
previous water year as the first entry. Entries to the table should
be made automatically each time a new shift curve is developed
and put into use during the current water year. The table should
include only defined information, not extrapolated parts of the
shift curve. The table should be accessible at any time. It should
include, at a minimum, the following items for each shift curve.
• Shift curve number
•Beginning date and time
• Ending date and time (if used)
•Minimum gage height
• Shift corresponding to minimum gage height
•Maximum gage height
• Shift corresponding to maximum gage height
• Name of user
• Date shift curve entered
9. Primary Computations
Primary computations are the functions that convert input
data, such as gage height, velocity index, and other auxiliary
data, into time series of unit values, daily values, monthly val-
ues, and annual values of discharge, mean velocity, reservoir
contents, and other output parameters. The conversion process
is dependent on the type of gaging station and, except for stage-
only stations, always will require the use of at least one rating
Stage
Shift
Time
+
0
_
Figure 9. Example plot of time-stage and series shifts.
60 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
curve. To carry out the conversion process, previously devel-
oped data and information will be required, such as time series
of input variables, correction diagrams, shift curves, and rating
tables. The conversion should be carried out with minimal inter-
action from the user, and should produce files of information
that can be used to produce tables and graphs that commonly are
referred to as primary output.
9.1 Unit Value Computations
Unit value files of uncorrected input parameters, such as
gage height and velocity index, are entered to the electronic pro-
cessing system as described in section 4.1. Also, specific infor-
mation such as parameter correction diagrams, shift curves, and
rating curves are entered as described previously. The primary
computations should produce additional unit values files of spe-
cific output parameters, dependent on the station type. These
unit values and their associated time tags are saved for the pur-
pose of computing daily mean values, various statistics, and for
archiving. The unit values files that should be computed for
each type of station are described in sections 9.1.1 and 9.1.9.
Most gaging stations use gage height as the input parame-
ter, however, some stations use elevation above NGVD as the
input parameter (for example, reservoir and tide stations). For
some of these stations, the original data are recorded as gage
heights above an arbitrary datum, and then converted to eleva-
tion as described in section 5.4.1.2. The computations in terms
of either gage height or elevation, depending on the most
common usage at each type of gage are described in sections
9.1.1 through 9.1.9.
Rating curves are used extensively in the conversion of
input parameters to unit value files of output parameters. Occa-
sionally, the range of the input parameter may exceed the range
of the defined rating. In such cases, the electronic processing
system should not automatically extrapolate the rating curve,
but rather, should insert a flag at points in the unit values file
where the rating is exceeded to alert the user. The user then may
make necessary extrapolations, and perform a new primary
computation to complete the files.
9.1.1 Stage-Only Stations
Stage-only stations are those stations where unit and daily
mean values of gage height, and associated statistics, are
required. For this type of station, only the unit values files of
gage-height data and the gage-height correction information are
needed. Primary computations should create the following unit
values files. Unless otherwise noted, each unit value file should
be saved for further use, and for archiving.
• Gage-height corrections—The electronic processing
system should evaluate and compute the gage-height
correction that corresponds to each input value of gage
height. gage-height corrections include instrument
errors, gage datum errors, and gage datum conversions
(for example, conversion to NGVD), as described in
section 5.4. The computations should use each correc-
tion and correction diagram, as defined by the user, and
as described in section 5.4. The corrections and correc-
tion diagrams should be interpolated by time and stage,
as required, and according to the interpolation proce-
dure described in section 5.4.2.3. If two or more correc-
tions or correction diagrams apply to the same time
period, the gage-height correction should be deter-
mined from each one independently for each time step,
and summed to produce the cumulative correction for
each time step. All gage-height corrections should be
rounded to standard gage-height precision (usually
hundredths of a foot, unless specified otherwise) before
using them in further calculations. The resulting time
series of cumulative gage-height correction values
should be saved as a working file, and for later
archiving.
• Corrected gage heights—A unit values file of corrected
gage heights should be computed by adding the cumu-
lative gage-height correction (see above) to the input
unit values of gage height for each time step. This file
of corrected gage heights is considered the final, and
most accurate, gage-height record for the gaging sta-
tion. The file also should be saved for further computa-
tions, and for archiving.
9.1.2 Stage-Discharge Stations
Stage-discharge stations are those stations where unit and
daily values of discharge are computed, based on unit values of
gage height and a stage-discharge rating curve. This station is
the most common type of gaging station, and requires unit
values files of gage height and information defining gage-
height corrections and shift adjustments. Unless otherwise
noted, each unit value file should be saved for further use, and
for archiving.
• Gage-height corrections—A file of unit values of
cumulative gage-height corrections should be com-
puted and saved for each unit value of gage height, as
described for stage-only stations in section 9.1.1.
• Corrected Gage Heights—A file of unit values of cor-
rected gage heights should be computed and saved, as
described for stage-only stations in section 9.1.1.
• Shift Adjustments—Unit values of shifts should be
computed for each unit value of corrected gage height.
These shifts should be based on the shift curves defined
by the user, and for the applicable time period. Interpo-
lation of shifts by time and stage should be performed
with the electronic processing system, according to the
method described in section 8.4.4. All unit values of
shifts should be rounded to standard gage-height preci-
sion, usually hundredths of a foot, before using them in
further computations. The computed unit value shifts
9. Primary Computations 61
for each gage height and time step should be saved in a
unit values file for further use, and for archiving.
• Discharge—Unit values of discharge should be com-
puted by temporarily adding the shift adjustment to the
corrected gage height for each time step. The corrected
and shifted gage height then should be used to deter-
mine the corresponding discharge from the applicable
rating curve. The shift-adjusted gage height is a work-
ing value only, and should not permanently alter the
gage height. It is not required that the shift-adjusted
gage heights be saved. The computed unit values of dis-
charge, however, should be saved for later use, and for
archiving.
For the low end of the rating, and if the rating is defined to zero
discharge, all shift-adjusted gage heights that are lower than the
gage height of zero flow will be assigned a unit value discharge
of zero. If the rating is not defined to zero flow, and a shift
adjusted gage height is below the lowest gage height of the rat-
ing, a flag should be set indicating the rating was exceeded on
the low end. Rating extrapolations can be made by the user at a
later point in the processing.
9.1.3 Velocity Index Stations
Velocity index stations are those stations where unit values
of discharge are computed on the basis of unit values of gage
height, cross-section area, an index velocity, mean stream
velocity, and a velocity adjustment factor (optional). At least
two rating curves are required, (1) a stage-area rating, and (2) an
index velocity and mean stream velocity rating. A third rating
sometimes is used, relating stage to a velocity adjustment fac-
tor. Information defining gage-height corrections, index-veloc-
ity corrections, and index-velocity shift adjustments also are
required.
Two unit value input files are used for velocity index sta-
tions, (1) an input file of unit values of gage height, and (2) an
input file of unit values of index velocity. For various reasons,
these files may not have corresponding and simultaneous time
steps, which is required for the unit value computations of dis-
charge. If the time steps for the two files do not correspond, the
electronic processing system should automatically interpolate
each file to provide estimated unit values corresponding to all
recorded times of both files. That is, the gage-height file should
be interpolated so that an estimated gage height is available for
all time steps of the index velocity file, and conversely, the
index velocity file should be interpolated so that an index veloc-
ity is available for all time steps of the gage-height file. There-
fore, this method doubles the size of each of the input unit
values files. The electronic processing system should flag, save,
and archive all estimated unit values, together with the recorded
unit values.
Unit value files should be computed with the electronic
processing system for the following parameters. Unless other-
wise noted, each unit value file should be saved for further use,
and for archiving.
• Gage-height Correction—A file of unit values of
cumulative gage-height corrections should be com-
puted and saved for each unit value of gage height
(including estimated values), as described for stage-
only stations in section 9.1.1.
• Corrected Gage Heights—A file of unit values of cor-
rected gage heights should be computed by adding the
gage-height corrections to the corresponding unit
values of gage heights.
• Velocity Adjustment Factor—If a rating of gage height
and velocity adjustment factor is used for the gaging
station, a velocity adjustment factor should be com-
puted from that rating for each unit value of corrected
gage height. Shift adjustments are not applied to gage
height for use with the velocity adjustment factor rat-
ing. If a velocity factor rating is not used for the station,
then the velocity adjustment factor of 1.00 is used for
all gage heights. Velocity adjustment factors should be
rounded to two decimal places for application pur-
poses.
• Cross-Section Area—The cross-sectional area should
be computed for each unit value of gage height, using
the stage-area rating.
• Index Velocity Correction—Correction values should
be computed for each input value of index velocity
(including estimated values), based on the index veloc-
ity correction value diagrams, and the methods of inter-
polation described in section 5.4. All index velocity
correction values should be rounded to standard veloc-
ity precision, usually hundredths of a foot per second.
• Corrected Index Velocity—Each input value of index
velocity should be corrected by adding the index veloc-
ity correction value to the corresponding value of the
input index velocity.
• Index Velocity Shifts—Shifts for each value of the cor-
rected index velocity should be computed based on the
velocity shift curves, and the interpolation procedure
described in section 8.4. All velocity shifts should be
rounded to standard velocity precision, usually hun-
dredths of a foot per second, before applying to further
computations.
• Mean Rating Velocity—The mean rating velocity
should be computed for each shift adjusted value of the
corrected index velocity by using the rating of index
velocity and mean velocity.
• Mean Stream Velocity—The mean stream velocity
should be computed for each time step by multiplying
the mean rating velocity times the velocity adjustment
factor.
• Discharge—The unit values of discharge should be
computed by multiplying each unit value of cross-sec-
tional area times the corresponding value of mean
stream velocity.
62 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
For some velocity index stations, two or more horizontal
subsections may be present, each of which has its own set of
unit values. For these stations, unit values files are computed for
each subsection as described above. Unit values of the total dis-
charge for the stream for each time step is computed as a sum-
mation of the corresponding unit values of the subsection dis-
charges. If time steps for the subsections do not correspond,
interpolation of unit values will be required.
For streams where two or more index velocity meters are
positioned to measure velocity at different vertical positions, a
velocity averaging procedure should be used to compute an
average index velocity for the stream. Various averaging proce-
dures are possible, depending on the gage configuration and the
number of index velocity gages that are used. The electronic
processing system should provide for user-defined equations to
compute average index velocity. The ratings for such a station
are based on the average index velocity. All other aspects of
computing unit values of discharge for the stream are the same
as described above.
9.1.4 Slope Stations
Slope stations are those stations where discharge is com-
puted on the basis of a stage-discharge relation that is adjusted
for variable water-surface slope. Water-surface slope cannot be
measured directly, so the water-surface fall between the base
gage and an auxiliary gage is used as an indicator of slope. The
auxiliary gage preferably is located downstream from the base
gage, at a distance that provides a measurable fall but does not
introduce hydraulically appreciable channel changes or tribu-
tary inflow. For some sites, the auxiliary gage may be located
upstream, but this is not advised because the water-surface
slope in the upstream reach is not as representative of backwater
conditions as it is in the downstream reach.
Computation of discharge at a slope station requires unit
values of gage height at the base gage and the auxiliary gage.
Three ratings are required: (1) stage-discharge, (2) stage-fall,
and (3) fall ratio and discharge ratio. Information defining gage-
height corrections for the base gage and the auxiliary gage, and
shift adjustments for the base gage, also are required.
Timing accuracy of unit-value data is very important at
each gage, because water-surface fall computations require that
time synchronous stage data be available for the base gage and
the auxiliary gage. Even with the best timers and time-correc-
tion methods, it is not always possible to obtain this kind of
accuracy, and stage data will sometimes be recorded and/or
time corrected to different time steps for the two gages. For such
situations, the stage data for the base gage should be interpo-
lated so that estimated stage values are available for each corre-
sponding stage value at the auxiliary gage. Likewise, the stage
data at the auxiliary gage should be interpolated so that esti-
mated stage values are available for each corresponding stage
value at the base gage. This procedure effectively doubles the
number of stage values at each gage, half of which are measured
values, and half are estimated values. The electronic processing
system should flag, save, and archive all estimated unit values,
together with the recorded unit values.
Computations of discharge using the slope method are
subject to constraints that should be checked and applied for
each unit value computation. These constraints are listed below.
1. Slope ratings should not be used if the measured fall values
are negative. In these cases, discharges should not be com-
puted and the electronic processing system should issue a
warning that negative fall values have been encountered.
2. Slope affected ratings may apply throughout the range in
stage measured at a station, or they may apply only for a
specific range in stage. The user should be allowed to
designate the lower and upper limits of the slope rating by
entering a minimum gage height and a maximum gage
height, below and above which the slope rating procedures
should not be used. Discharge should be computed
directly from the stage-discharge rating for gage heights
that are outside these limits.
3. Slope ratings may, in some situations, have maximum fall
constraints. That is, for measured fall values exceeding a
designated amount, or for measured fall exceeding the fall
from the stage-fall rating, no slope adjustments should be
applied. The user should be allowed to enter a maximum
fall so that when measured falls exceed this value, slope
adjustments will not be made. Likewise, the user should
be allowed to designate that when measured fall exceeds
the rating fall slope adjusted computations will not be
made. For both of these situations, unit values of discharge
should be computed by direct application of the stage-
discharge rating.
4. For some slope stations, constraints 2 and 3 both may
apply, and should be checked.
Unit value files should be computed with the electronic
processing system for the following parameters, subject to the
above constraints. Unless otherwise noted, each unit value file
should be saved for further use and archiving.
• Gage-height Corrections, Base Gage—A file of unit
values of cumulative gage-height corrections for the
base gage should be computed and saved for each cor-
responding unit value of gage height (including esti-
mated values), as described for stage-only stations in
section 9.1.1.
• Corrected Gage Heights, Base Gage—A file of unit
values of corrected gage heights for the base gage
should be computed by adding the gage-height correc-
tions for the base gage to the corresponding unit values
of gage heights.
• Gage-height Corrections, Auxiliary Gage—A file of
unit values of cumulative gage-height corrections for
the auxiliary gage should be computed and saved for
each corresponding unit value of gage height (including
estimated values), as described for stage-only stations
in section 9.1.1.
9. Primary Computations 63
• Corrected Gage Heights, Auxiliary Gage—A file of
unit values of corrected gage heights for the auxiliary
gage should be computed by adding the gage-height
corrections for the auxiliary gage to the corresponding
unit values of gage heights.
• Measured Water Surface Fall—A file of unit values of
measured water-surface fall should be computed by
subtracting each unit value of gage height at the auxil-
iary gage from the corresponding gage height at the
base gage. If the auxiliary gage is located upstream
from the base gage, fall should be computed by sub-
tracting the base gage height from the auxiliary gage
height.
• Shift Adjustments—For slope stations, shift adjust-
ments are used only for the stage-discharge rating for
the base gage. A unit values file of shift adjustments
should be computed for each base gage height, includ-
ing estimated values, by using the defined shift curves
and the time/stage interpolation procedures described
in section 8.4. If shift curves are not applicable for spe-
cific time periods, shifts should default to zero for that
time period.
• Rating Discharge—Unit values of rating discharge are
computed for each unit value of shift adjusted gage
height for the base gage, using the stage-discharge
rating for the base gage. The rating discharge is an
unadjusted discharge value, and does not represent the
true discharge of the stream.
• Rating Fall—Unit values of rating fall are computed
for each unit value of gage height (not shift adjusted)
for the base gage, using the stage-fall rating for the base
gage.
• Fall Ratio—Unit values of fall ratio are computed by
dividing the measured water-surface fall by the rating
fall.
• Discharge Ratio—Unit values of the discharge ratio
are computed using the rating curve of fall ratio and dis-
charge ratio.
• Discharge—Unit values of discharge are computed by
multiplying the rating discharge times the discharge
ratio. The resulting discharge represents the true dis-
charge of the stream.
9.1.5 Rate-of-Change-in-Stage Stations
Rate-of-change-in-stage stations are those stations where
discharge is computed on the basis of a stage-discharge relation
that is adjusted for variable rates of change in stage. Computa-
tion of discharge is based on the Boyer Method and requires
unit values of gage height. Two ratings are required, (1) a stage-
discharge rating, and (2) a stage-1/US
c
rating. Information
defining gage-height corrections and shift adjustments also are
required.
Computation of discharge using the Boyer Method is sub-
ject to constraints that should be checked and applied for each
unit value computation. These constraints are as follows.
1. Rate-of-change-in-stage ratings apply only to high dis-
charges where channel control conditions are effective.
The user should be allowed to specify a minimum gage
height and a maximum gage height, below and above
which the rate-of-change-in-stage computations should not
be applied. Discharge should be computed directly from
the stage-discharge relation when the stage is outside these
limits.
2. Rate-of-change-in-stage computations are frequently not
made when the Boyer adjustment factor results in only a
small change of the rating discharge. The electronic
processing system should use default values of 0.96 to
1.04 as the range of Boyer adjustment factors for which
adjustments would not be made.The user should be
allowed to change these values, if necessary (for example,
to achieve smoothness of the computed unit values of
discharge).
Unit value files should be computed with the electronic
processing system for the parameters listed below, subject to
the above constraints. Unless otherwise noted, each unit value
file should be saved for further use and archiving.
• Gage-height Corrections—A file of unit values of
cumulative gage-height corrections should be com-
puted and saved for each corresponding unit value of
gage height, as described for stage-only stations in sec-
tion 9.1.1.
• Corrected Gage Heights—A file of unit values of cor-
rected gage heights should be computed by adding the
gage-height corrections to the corresponding unit
values of gage heights.
• Rate of Change in Stage—A rate-of-change in stage
(dG/dt) should be computed for each unit value of cor-
rected gage height that is within the range of gage
heights defined by the minimum and maximum con-
straint. First, the difference in stage is computed by
subtracting the previous unit value of corrected gage
height from the next unit value of the corrected gage
height. This difference in gage height is converted to
the rate-of-change in stage, in feet per hour, by dividing
it by the time difference of the previous and next unit
values. This method of computation provides an aver-
age rate-of-change-in-stage for the time period extend-
ing one time interval before and one time interval after
the current unit value of gage height. The algebraic sign
of the computed rate-of-change-in-stage should be
retained as computed. A positive sign indicates a rising
stage, and a negative sign indicates a falling stage.
• Shift Adjustment—For rate-of-change-in-stage sta-
tions, shift adjustments are used only for the stage-dis-
charge rating. A unit values file of shift adjustments
should be computed for each corrected gage height by
64 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
using the defined shift curves and the time/stage inter-
polation procedures described in section 8.4. If shift
curves are not applicable for specific time periods,
shifts should default to zero for that time period.
• Rating Discharge—Unit values of rating discharge are
computed for each unit value of shift adjusted gage
height using the stage-discharge rating. The rating dis-
charge is an unadjusted discharge value, and does not
represent the true discharge of the stream for periods
when rate-of-change adjustments are applicable.
• Boyer Factor, 1/US
c
—The Boyer Factor should be
computed for each corrected gage height (not shift
adjusted) that is within the range of gage heights
defined by the minimum and maximum constraint, by
application of the stage-1/US
c
rating.
• Discharge Adjustment Factor—Unit values of the dis-
charge adjustment factor, F
adj
, are computed based on
the Boyer Factor and the rate-of-change-in-stage, by
using the following equation. Discharge adjustment
factors should be computed only for gage heights that
are within the range of gage heights defined by the min-
imum and maximum constraint as
. (30)
• Discharge—Unit values of discharge are computed by
multiplying the rating discharge times the discharge
adjustment factor. All unit values of discharge that are
based on adjustment factors from 0.96 to 1.04, by
default, should not be used unless overridden or other-
wise specified by the user. Instead, the rating discharges
based on the shift adjusted gage heights should be used
directly.
9.1.6 Reservoir Stations
Reservoir stations are those stations where unit and daily
values of reservoir elevation and reservoir contents are
required. If only reservoir elevation is required, no rating is
needed. However, if reservoir contents are required, then a
rating of reservoir elevation and contents is needed. Input
requires unit values of elevation and information defining ele-
vation corrections. Generally, for reservoir stations, the term
elevation is used rather than gage height because the elevation
above National Geodetic Vertical Datum (NGVD) is used for
many reservoir gages. However, gage heights are allowed and
used at many reservoir stations. Unit values files should be
computed with the electronic processing system for the param-
eters listed below. Unless otherwise noted, each unit value file
should be saved for further use and archiving.
• Elevation Correction—A file of unit values of cumula-
tive elevation corrections should be computed and
saved for each corresponding unit value of elevation, as
described for stage-only stations in section 9.1.1.
• Corrected Elevations—A file of unit values of cor-
rected elevations should be computed by adding the
elevation corrections to the corresponding unit values
of elevations.
• Reservoir Contents—A file of unit values of reservoir
contents should be computed by application of the cor-
rected elevations to the elevation-contents rating.
9.1.7 Tide Stations
Tide stations are those stations located in estuaries and
along tidal affected rivers and streams to provide the daily infor-
mation on diurnal and/or semi-diurnal variations of surface-
water levels in those areas. Tide stations may be set to an arbi-
trary datum or to an elevation based on the National Geodetic
Vertical Datum (NGVD). When an arbitrary datum is used, unit
values of elevation are determined by adding a constant datum
conversion to the unit values of gage height. No other conver-
sions to other parameters are required, therefore, no ratings are
required. Information defining gage height or elevation correc-
tions also is required. Each unit value file should be saved for
further use and archiving.
• Gage-Height or Elevation Correction—A file of unit
values of cumulative gage height or elevation correc-
tions should be computed and saved for each corre-
sponding unit value of gage height or elevation as
described for stage-only stations in section 9.1.1. This
correction value is separate from the datum-conversion
value used to convert gage height to NGVD.
• Corrected Gage Height or Elevation—A file of unit
values of corrected gage heights or elevations should be
computed by adding the gage-height or elevation cor-
rections to the unit values of gage heights or elevations.
9.1.8 Hydraulic Structure Stations
Hydraulic structure stations are those stations where unit
and daily values of discharge are computed using special ratings
and equations for spillways, gates, turbines, pumps, siphons,
and other controlled conveyances. A special software program
developed by C.L. Sanders, USGS, South Carolina District,
(written communication, 1997) is available for this purpose.
The basic theory and concepts are described by Collins (1977).
Input data may include unit values of headwater gage heights,
tailwater gage heights, individual gate openings for each gated
conveyance, turbine pressures, lockages, and other variables as
required for a specific site. Hydraulic structure gaging stations
are extremely complex and may have many sub-units (individ-
ual gates, turbines, and others) for which unit values of dis-
charge are computed. Unit values of total discharge are com-
puted as a summation of the individual subunits. Because of the
complexity and variability of hydraulic structure gages, a listing
of unit values files will not be given here. However, the elec-
F
adj
1
1
US
c
---------
dG
dt
-------
+=
9. Primary Computations 65
tronic processing system should save all unit values files for fur-
ther use and archiving.
9.1.9 BRANCH Model Stations
A BRANCH model gaging station utilizes a calibrated dig-
ital computer model for simulating the unsteady flow in a chan-
nel reach, usually affected by variable backwater. The model
calibration requires basic field data, principally cross-section
definition at a number of locations in the gaged reach, rough-
ness coefficients, calibration discharge measurements, and
gage-height data at the upstream and downstream end of the
gaged reach. Details of calibration and computation are given
by Schaffrannek and others (1981). Primary computations
require unit values of gage height at the upstream and down-
stream ends of the reach, as given below. Information defining
gage-height corrections for the upstream and downstream gages
is required.
• Gage-height Corrections, Upstream Gage—A file of
unit values of cumulative gage-height corrections for
the upstream gage should be computed and saved for
each corresponding unit value of gage height (including
estimated values), as described for stage-only stations
in section 9.1.1.
• Corrected Gage Heights, Upstream Gage—A file of
unit values of corrected gage heights for the upstream
gage should be computed by adding the gage-height
corrections for the upstream gage to the corresponding
unit values of gage heights.
• Gage-height Corrections, Downstream Gage—A file
of unit values of cumulative gage-height corrections for
the downstream gage should be computed and saved for
each corresponding unit value of gage height (including
estimated values), as described for stage-only stations
in section 9.1.1.
• Corrected Gage Heights, Downstream Gage—A file of
unit values of corrected gage heights for the down-
stream gage should be computed by adding the gage-
height corrections for the downstream gage to the cor-
responding unit values of gage heights.
BRANCH model gages have a unique characteristic, in
that the parameters of gage height, mean stream velocity, and
discharge are computed for each cross-section location, as well
as at the upstream and downstream gage locations. For this rea-
son, unit values of each of these parameters, for each cross sec-
tion, can be saved for future use and archiving, if desired. The
electronic processing system should allow the user to designate
which output parameters, and for which cross sections and gage
sites, should be saved for future use and archiving.
9.2 Daily Value Computations
Various kinds of daily values are computed for each
station type, and are based on the unit values files
described in section 9.1. Daily values for the various parameters
consist of mean values, minimum instantaneous values, maxi-
mum instantaneous values, and instantaneous values at selected
times. Daily values for a gaging station usually are computed
for the local time zone designation, for the location of the
gaging station. This computation includes the use of daylight
savings time wherever applicable. However, the electronic pro-
cessing system should allow computation of daily values for
any other time zone, as selected by the user. For additional
information on time zones, see sections 5.1 and 5.2.
The electronic processing system should allow the user to
compute daily values for temporary use and study, without
requiring that they be saved and archived. Such files of daily
values could be used for review and comparisons before final-
ization of the records.
9.2.1 Daily Mean Values
Daily mean values, frequently referred to as daily values,
consist of a time-weighted arithmetic mean of selected parame-
ters, and are computed from the files of unit values. Daily mean
values may be computed for the following parameters.
• Gage height
• Discharge
• Cross-section area (index velocity stations)
• Index velocity
•Mean stream velocity
•Fall (slope stations)
• Elevation (reservoir and tide stations)
• Contents (reservoir stations)
A file of all computed daily mean values should be saved
for future use and archiving.
The time-weighted arithmetic method of computing daily
mean values is referred to as the trapezoidal method. The trap-
ezoidal method is a mathematical integration of the unit value
hydrograph and provides an accurate computation of the mean
parameter value. With a large number of instantaneous values
for each day, the trapezoidal method closely approximates
actual integration.
The trapezoidal method assumes that all unit values are
instantaneous values, and that each unit value has a specific,
designated time of occurrence. The time interval between unit
values may be constant or variable. The file of unit values used
for the computation of the daily mean value by the trapezoidal
method must include a unit value at the midnight time for each
day. If actual values are not recorded for the midnight time, a
unit value should be interpolated based on the recorded unit
values on either side of the midnight time. These interpolated
midnight values should be flagged as interpolated, and should
be retained in the unit values file for future use and archiving.
The equation for the trapezoidal method is
(31)
Q
q
0
q
1
+
2
-----------------
t
1
t
0
–()
q
1
q
2
+
2
-----------------
+ t
2
t
1
–()…
q
n 1–()
q
n
+
2
---------------------------
+ t
n
t
n 1–()
–()
t
n
t
0
–
------------------------------------------------------------------------------------------------------------------------------------------------------------------------=
66 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
where
Q = daily mean parameter value (In the above equation, Q
represents discharge; however, the same equation can
be used for any other parameter, such as gage height,
velocity, and others)
q
0
= the parameter unit value at the midnight time at the
beginning of the day,
q
1
, q2....., q(
n-1
) = consecutive unit values of the parame-
ter during the day,
q
n
= the parameter unit value at the midnight time at the
end of the day,
t
0
= midnight time at the beginning of the day, or zero
time,
t
1
, t
2
......, t(
n-1
) = consecutive times corresponding to the
parameter unit values during the day, and
t
n
= midnight time at the end of the day, or 24.00 hour
time. Note that all times must be expressed in hours and
decimal parts of a hour.
Daily values will not be computed for days when time gaps
exceed a value specified as the abort interval. The abort interval,
by default, is 2 hours; however, the user should be allowed to
change this interval to any other value less than 24 hours.
9.2.2 Daily Minimum and Maximum Values
The minimum and maximum values for some of the
parameters are required for each day. These values are deter-
mined from the unit value files for the various parameters, and
the selection process should consider all recorded and interpo-
lated unit values for each day, including the midnight values at
the beginning and end of each day. For some parameters, corre-
sponding values of other parameters also should be determined.
The parameters requiring maximum and minimum values
for each day and for each station type, and the corresponding
unit values required for each maximum and minimum are
shown in table 14. Not all tidal stations are included in table 14.
Tidal stations require special computations to determine peak
and trough elevations for semi-diurnal, diurnal, and mixed tidal
cycles. The computation procedures for determinations at tidal
stations are described in section 9.2.4.
9.2.3 Daily Values at Selected Times
Some stations require additional daily values at selected
times for some parameters. For instance, reservoir stations
sometimes require daily elevation and contents at specific
times, such as 0800, 1200, or 2400. If unit values are not avail-
able at the specified times, interpolated values should be used.
The user should be able to specify the parameter and time for
which selected daily values are required, for all station types.
9.2.4 Daily Values for Tidal Stations
Tidal stations require the determination of the gage heights
or elevations of tidal peaks and troughs for diurnal and semi-
diurnal variations of the water-surface level. The unit values file
of the corrected gage height or elevation data are examined
sequentially to determine the two high tides and the two low
tides for each day for semi-diurnal fluctuations. The procedure
for computing daily values for tidal stations also recognizes
diurnal and mixed fluctuations when they occur. The following
discussion is excerpted from Hutchinson and others (1977).
“In order to find true tidal peaks and troughs which
occur once or twice in relation to the lunar day rather
than the solar day, the record is NOT broken up into
groups of observations in a calendar day before pro-
cessing. Instead, the whole record is scanned contin-
uously for successive peaks and troughs within
periods of given length following the time of the pre-
vious extreme. After each extreme is found, the cal-
endar day in which it occurred and time is
determined. This completely eliminates any confu-
sion with inclusion or exclusion of extremes occur-
ring just before or just after midnight.
“The method of finding successive tidal peaks and
troughs is to look for an opposite extreme in a
selected time period (normally 10-1/2 hours) follow-
ing each recognized peak or trough. That is, when a
tidal peak is found (and its date and time are stored) a
search is made for the lowest stage in the selected
time period following the time of the previous tidal
peak. Then having found the time of this tidal trough,
a search is made for the highest stage in the selected
time period following the time of the previous tidal
trough. Comparison of two peaks found within a cal-
endar day and two troughs found within the same
calendar day are used to assign each as a HIGH-
HIGH, a LOW-HIGH, a HIGH-LOW, or a LOW-
LOW for the day.
9. Primary Computations 67
Table 14. Parameters requiring daily maximum and minimum values computed for various station types
Station Type Parameter Requiring Maximum and Minimum Corresponding Values for Parameters
Stage only Corrected gage height Gage-height correction
Stage—discharge Corrected gage height Gage-height correction, shift
Discharge —
Velocity—index Corrected gage height Gage-height correction, velocity factor, area, corrected
index velocity, mean stream velocity, discharge
Corrected velocity index Index velocity correction, index velocity shift
Mean stream velocity —
Discharge —
Slope Corrected base gage height Gage-height correction, shift, measured fall, rating fall,
fall ratio, discharge ratio, discharge
Corrected auxiliary gage height Gage-height correction
Measured fall —
Discharge —
Rate-of-change in stage Corrected gage height Gage-height correction, shift, rate-of-change, Boyer fac-
tor, discharge adjustment factor, rating discharge, dis-
charge
Discharge —
Reservoir Corrected elevation Elevation correction
Contents —
Hydraulic structure Corrected headwater gage height Gage-height corrections for headwater
Corrected tailwater gage height Gage-height corrections for tailwater
Discharge —
BRANCH Corrected upstream gage height Gage-height corrections for upstream gage
Corrected downstream gage height Gage-height corrections for downstream gage
Discharge —
“Although the normal tide on most of the United
States coastline is semi-diurnal, at a few places the
tides are diurnal or are mixed semi-diurnal. This pro-
gram tries to give meaningful results in a situation by
the following logic. Starting each search for a peak or
trough, a normal, semi-diurnal tidal cycle is assumed
and the length of the selected time period for the
search is set at about 10-1/2 hours (0.44 day). This
length of the search period was picked so as to be
long enough to include the normal time of occurrence
of the next peak or trough for a semi-diurnal tide
(which should occur about 6-1/2 hours after the pre-
ceding trough or peak) and short enough to avoid
confusion with the advance side of the next following
tidal wave if the two tidal waves are of greatly differ-
ent magnitude. (If a 12-hour search period were used,
confusion could occur such as when the second tidal
wave of the day is so much higher than the first that
the water level 12 hours after the previous tidal
trough is rapidly rising and already higher than it was
at the time of the first real peak which occurred about
6-1/2 hours after the previous tidal trough).
68 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
“In order to be able to produce meaningful results for
sites where the tide is actually diurnal or is a mixture
of semi-diurnal and diurnal, an additional test is
made after each search for the next apparent extreme.
If the next extreme is found to occur in the last hour
of the 10-1/2 hour search period, it is assumed that
this extreme is not a true tidal peak or trough in a
semi-diurnal cycle but is instead falling toward a
trough or rising toward a peak in a diurnal tidal
cycle. Then in order to find the real tidal peak or
trough in this longer cycle, that particular search
period is extended by another 12 hours and the new
results used as the next peak or trough. However,
after finding the next tidal peak or trough, the follow-
ing search is again made for an initial period of 10-
1/2 hours so that a change back from a diurnal tide to
a semi-diurnal tide is not missed.”
The daily values of HIGH-HIGH, LOW-HIGH, HIGH-
LOW, and LOW-LOW determined in the above procedure
should be saved for further use, and for archiving. In addition,
the cumulative elevation correction values corresponding to
each of the peak and trough elevations should be saved and
archived. The daily mean gage height and/or elevation also may
be computed for a tidal station, as is done for a stage only sta-
tion, and these values should be saved and archived.
9.3 Summary of Primary Computations
Primary computations include the determination of unit
values and daily values for numerous parameters, as described
in sections 9.1 and 9.2. It is important and necessary to summa-
rize the results in tables that can be used for review, analysis,
and for publication. Standard formatted tables include unit val-
ues, primary computations, diagnostics, and daily value tables.
The electronic processing system should allow for the design of
other summary tables, as needed, and as specified by the user.
9.3.1 Unit Values Tables
The electronic processing system should provide a flexible
array of unit values tables to allow for the analysis and review
of individual parameters, or selected groups of parameters. For
instance, a unit values table may show only the final, corrected
values of gage height for a selected period of time; or the unit
values table may show the final gage-height values and the cor-
responding discharge values. The user should select the input
parameters to a unit values table. The unit values should be dis-
played in chronological order, and generally grouped by day,
month, and year. The user also should specify selected time
intervals for a unit values table. For instance, an hourly table
may be selected, even though 15-minute unit values are avail-
able or, even-hour unit values may be selected that require inter-
polation of unit values that are not recorded on the even-hour.
9.3.2 Primary Computations Tables
Primary computations involve the application of various
user instructions to derive the final discharge record (or other
parameter such as reservoir contents, tide, and others) for a
gaging station. These instructions include gage-height correc-
tions, shifts, and rating curves. The computations should be dis-
played in a table that shows input data, and various computed
information so that they can be easily reviewed. Traditionally,
two formats have been utilized for displaying primary compu-
tations, (1) the historical format, and (2) the standard format.
Selection of either format is optional.
The main difference between the historical format and the
standard format of a primary computation is that the historical
format shows hourly values of input data (for example, gage
heights). The standard format provides more information than
the historical format regarding the computations. Other differ-
ences are present between the formats, but these are mainly in
the arrangement of the data and information.
Each gaging station type, such as stage-discharge, slope,
velocity-index, and others, will have primary output formats
specifically designed for the station type. A listing of items, by
station type, that should be included in a primary computation
form, is shown in table 15. Arrangement of the information is
not critical. A slightly modified version of a traditional histori-
cal primary output is shown in figure 10, and a standard format
is shown in figure 11, each for a stage-discharge station. Pri-
mary computation tables for other gaging station types should
be similarly designed.
9. Primary Computations 69
Table 15. Items required for primary output tables for various gaging station types
Item
Gaging-StationType
Stage
Only
Stage-
Dis-
charge
Velocity
Index
Slope
Rate-of-
Change
in Stage
Reser-
voir
Tide Structure
BRANCH
Model
Header Information
Station identification number X X X X X X X X X
Station name X X X X X X X X X
Water year information X X X X X X X X X
Date of primary processing X X X X X X X X X
Name of responsible user X X X X X X X X X
List of ratings used X X X X X
Unit value recording interval X X X X X X X X X
Station type (for example, processing
method)
XXXXX XXX X
Datum conversion (if applicable) X X X X X X X X X
Tabular Information
Date X X X X X X X X X
Hourly gage heights for base gage X X X X X
Daily maximum gage height X X X X X X X
Time of maximum gage height X X X X X X X
Shift corresponding to maximum gage
height
X X X
Gage-height correction corresponding to
maximum gage height
XXXXX X X
Daily minimum gage height X X X X X X X
Time of minimum gage height X X X X X X X
Shift corresponding to minimum gage
height
X X X
Gage-height correction corresponding to
minimum gage height
XXXXX X X
Daily mean gage height X X X X X X X
Daily maximum discharge X X X X X X
Time of maximum discharge X X X X X X
Daily minimum discharge X X X X X X
Time of minimum discharge X X X X X X
Daily mean discharge X X X X X X
Hourly discharges X X X X
Daily maximum index velocity X
Time of maximum index velocity X
Shift corresponding to maximum index
velocity
X
Index velocity correction for maximum
index velocity
X
Daily minimum index velocity X
Time of minimum index velocity X
70 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
Item
Gaging-StationType
Stage
Only
Stage-
Dis-
charge
Velocity
Index
Slope
Rate-of-
Change
in Stage
Reser-
voir
Tide Structure
BRANCH
Model
Index velocity correction for minimum
index velocity
X
Daily mean index velocity X
Daily maximum cross-section area X
Time of maximum cross-section area X
Daily minimum cross-section area X
Time of minimum cross-section area X
Daily mean cross-section area X
Daily maximum stream velocity X
Time of maximum stream velocity X
Daily minimum stream velocity X
Time of minimum stream velocity X
Daily mean stream velocity X
Daily maximum reservoir contents X
Time of maximum reservoir contents X
Daily minimum reservoir contents X
Time of minimum reservoir contents X
Daily mean reservoir contents X
Reservoir gage height at specified time X
Gage-height correction at specified time X
Reservoir contents at specified time X
Daily high-high gage height without
datum conversion
X
Daily high-high gage height with datum
conversion
X
Time of daily high-high gage height X
Correction for daily high-high gage height X
Daily low-high gage height without
datum conversion
X
Daily low-high gage height with datum
conversion
X
Time of daily low-high gage height X
Correction for daily low-high gage height X
Daily high-low gage height without
datum conversion
X
Daily high-low gage height with datum
conversion
X
Time of daily high-low gage height X
Correction of daily high-low gage height X
Table 15. Items required for primary output tables for various gaging station types—Continued
9. Primary Computations 71
Item
Gaging-StationType
Stage
Only
Stage-
Dis-
charge
Velocity
Index
Slope
Rate-of-
Change
in Stage
Reser-
voir
Tide Structure
BRANCH
Model
Daily low-low gage height without datum
conversion
X
Daily low-low gage height with datum
conversion
X
Time of daily low-low gage height X
Correction for daily low-low gage height X
Daily mean tide gage height without
datum conversion
X
Daily mean tide gage height with datum
conversion
X
Daily maximum gage height at auxiliary
gage
XX
Time of maximum daily gage height X X
Gage-height correction corresponding to
maximum auxiliary gage height
XX
Daily minimum gage height at auxiliary
gage
X X
Time of daily minimum gage height X X
Gage-height correction corresponding to
minimum auxiliary gage height
X X
Daily mean gage height at auxiliary gage X X
Daily maximum fall X
Time of daily maximum fall X
Daily minimum fall X
Time of daily minimum fall X
Maximum rate-of-change in stage X
Time of maximum rate-of-change in stage X
Maximum adjustment factor X
Time of maximum adjustment factor X
Minimum adjustment factor X
Time of minimum adjustment factor X
Table 15. Items required for primary output tables for various gaging station types—Continued
72 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
Figure 10. Example of a historical primary output of primary computations table.
72 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
9. Primary Computations 73
Figure 11. Example of a standard primary output of primary computations table.
9.0 Primary Computations 73
74 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
9.3.3 Diagnostics Tables
Diagnostics tables provide a means to review every com-
putation for each time step of the primary computations. The
table should be a line item listing, in chronological order of the
time steps, showing all input and computed values for each time
step of each day. Items required in the diagnostics table for each
type of gaging station are listed in table 16.
Table 16. Items required for diagnostics tables
Item
Gaging-Station Type
Stage
Only
Stage-
Dis-
charge
Velo-
city
Index
Slope
Rate-
of-
Change
in
Stage
Reser-
voir
Tide Structure
BRANCH
Model
Header Information
Station identification number XXXXXXXX X
Station name X X X X X X X X X
Water year information XXXXXXXX X
Date of primary processing X X X X X X X X X
List of ratings used XXXXX X
Station type (for example, processing
information)
X X X X X X X X X
Tabular information
Date XXXXXXXX X
Time X X X X X X X X X
Base gage height, without corrections or
adjustments
XXXXXXXX X
Base gage-height correction X X X X X X X X X
Base gage-height datum adjustment XXXXXXXX X
Base gage height, with corrections and
adjustments
X X X X X X X X X
Base gage-height shift X X X
Index velocity, without correction X
Index velocity correction X
Index velocity, with correction X
Index velocity shift X
Index velocity adjustment factor X
Mean stream velocity X X
Cross-section area X X
Discharge (mean stream velocity times
cross-section area)
X
Auxiliary gage height, without correc-
tion or adjustment
X X X
9. Primary Computations 75
Item
Gaging-Station Type
Stage
Only
Stage-
Dis-
charge
Velo-
city
Index
Slope
Rate-
of-
Change
in
Stage
Reser-
voir
Tide Structure
BRANCH
Model
Auxiliary gage-height correction X X X
Auxiliary gage-height datum adjustment X X X
Auxiliary gage height with correction
and adjustment
XXX
Measured Fall X
Rating Fall X
Fall ratio X
Discharge ratio (from ratio rating) X
Rating discharge X X X
Discharge, adjusted for slope X
Rate-of-change in stage X
Factor 1/USc X
Discharge adjustment factor X
Discharge, adjusted for rate-of-change-
in-stage
X
Reservoir contents X
Number of gates X
Discharge through gates X
Number of turbines X
Discharge through turbines X
Spillway discharge X
Weir discharge X
Pump discharge X
Siphon discharge X
Lockage discharge X
Leakage discharge X
Other discharge X
Total discharge, hydraulic structure sta-
tion
X
Discharge computed by BRANCH
model
X
Table 16. Items required for diagnostics tables—Continued
1
For structures’ gaging stations, base gage is headwater gage and auxiliary gage is tailwater gage.
76 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
9.3.4 Daily Values Tables
A daily values table is a listing of the daily values for each
day of the year, for selected parameters at a gaging station. Gen-
erally, daily values are the daily mean discharges for a gaging
station, but other parameters such as stage, elevation, reservoir
contents, or other statistics such as daily maximum, daily mini-
mum, and daily unit value at a specific time, may compose a
daily values table. The user should be allowed to specify time
periods in the daily values table, and to include multiple param-
eters in one table. In addition, the daily values table should
show monthly and annual totals, means, and extremes, as
appropriate. See section 13 for computation of monthly and
annual values.
9.3.5 Unit Values and Discharge Measurement
Comparison Table
A table where primary computation unit values are com-
pared to measured discharge should be produced for all gaging
stations where discharge measurements are made. This table
will be used to review the final results after the primary compu-
tations are completed, and to verify that all shifts, corrections,
and adjustments were applied correctly. The comparison should
be made using the mean time of the discharge measurement. At
a minimum, this table should include the following items.
• Date of discharge measurement
•Mean time of discharge measurement
•Measured discharge
• Computed unit value of discharge for same date and
time (interpolated, if necessary)
• Difference between measured discharge and computed
unit value discharge, (Q
m
- Q
uv
)
• Percent difference of measured discharge and com-
puted unit value discharge, 100(Q
m
- Q
uv
)/Q
uv
10. Hydrograph Plots
Hydrographs are useful for graphical viewing, verifica-
tion, editing, and comparisons of streamflow information,
including most of the basic information that contributes to the
primary computation of streamflow records. Hydrograph plots
of unit values of discharge, along with comparative plots of
other parameters, such as gage height, velocity, and shifts, and
supplementary data such as peak discharge, peak stage, and dis-
charge measurements, provide an excellent means of reviewing
and editing the primary computations. Likewise, hydrograph
plots of daily discharge records can be combined with
hydrograph plots of other station records, precipitation records,
and temperature records for review and editing purposes, as
well as providing a graphical summary of the records for visual
presentation and publication. Hydrograph requirements for
other purposes such as review and editing of unit value input
(section 5.3.4) and estimation of missing record (section 13.2.1)
are consistent with hydrograph requirements stated in this sec-
tion for review of primary computations.
All hydrograph plots, both unit value and daily value,
should be viewable on the computer monitor. In addition, the
user should have the option to plot all hydrographs on paper
plots. All scales and grid lines should be generated by the elec-
tronic processing system. Preprinted plotting forms are not
advised.
10.1 Unit Values Hydrographs
The electronic processing system should allow the user to
choose any of the unit values files for hydrograph plotting. Gen-
erally, hydrographs showing unit values of discharge will be of
most interest, but other unit values hydrographs, such as gage
height, elevation, and reservoir contents also may be required.
Other unit values files of supplementary information, such as
for shifts, gage-height corrections, auxiliary gage information,
and others should be superimposed on the same plot if these
additional parameter plots are specified. Also, unit value infor-
mation from other gaging stations, precipitation stations, and
temperature stations should be superimposed on the same plot,
as specified by the user.
When more than one unit values file is shown on a unit
values hydrograph plot, each should be clearly identified by a
distinctive plotting symbol. Individual scales should be shown
for each parameter, labeled with the correct parameter name and
units of measurement.
The abscissa scale for a unit values hydrograph plot is a
time scale, with hours being the primary unit of subdivision.
Each day, month, and year are shown as secondary subdivi-
sions. The ordinate scale should conform to the parameter being
plotted. Discharge scales should default to logarithmic, but
should be changeable to linear if specified. All other scales,
such as for gage height, elevation, shifts, rainfall, temperature,
and others, should default to linear scales. The range of the ordi-
nate scale should default to one that will include the full range
of the plotted unit values file, but should be changeable to any
specified range.
10.2 Daily Values Hydrographs
A daily values hydrograph is a traditional USGS method
for displaying the results of streamflow computations for a
gaging station. This hydrograph usually is an annual plot show-
ing the daily values for a water year, but can be for any other
period of time as selected by the user. Daily value hydrographs
usually are plots of daily mean discharge for a gaging station,
with comparative hydrograph plots of daily mean discharge for
one or more nearby gaging stations. For some stations, the daily
values hydrograph also may include daily values of precipita-
tion and/or temperature. Daily values hydrographs also can be
11. Computation of Extremes 77
used to display other parameters, such as gage height, elevation,
and reservoir contents.
When more than one daily values file is shown on a daily
values hydrograph plot, each should be clearly identified by a
distinctive plotting symbol. Individual scales should be shown
for each parameter, labeled with the correct parameter name and
units of measurement.
The abscissa scale for daily values hydrographs is a time
scale, with days being the primary subdivision. Months and
years are secondary subdivisions. The ordinate scale should be
logarithmic for discharge plots, unless otherwise specified by
the user. Other daily values parameters should be plotted using
linear scales. The range of the ordinate scale for the primary
parameter should default to one that will include the full range
of the daily values for the time period being plotted.
10.3 Supplementary Hydrograph Information
A few items of supplementary information are required, or
are optional, for both unit value and daily value hydrograph
plots. These include hydrograph identification information
(required), discharge measurement data (optional), and peak
information (optional).
• Station Number and Name—Each hydrograph plot
should include a heading that shows the station number
and name of the parameter of primary interest. If sup-
plementary hydrographs are plotted on the same plot,
they should be identified separately within the grid
area, using an explanation.
• Time Period of Hydrograph—The hydrograph heading
should state the time period covered by the plot. For
instance, water year 1996, calendar year 1996, January
1996 through June 1996, and others. The same period
of time is identified on the abscissa scale.
• Discharge Measurements—All discharge measure-
ments made during the time period of the hydrograph
plot should be plotted if specified by the user. Dis-
charge measurements should be plotted at the mean
time of each discharge measurement. The measured
discharge always should be plotted, and the adjusted
discharge also should be plotted if one is available. Dis-
charge measurements should be plotted as a small open
circle and identified with the measurement number
adjacent to the circle. Adjusted discharges should be
plotted with a distinctive symbol.
• Peak Measurements—For unit value stage and eleva-
tion hydrographs, peak stages and/or elevations (from
crest-stage gages and high water marks) may be plotted
if specified by the user. Peak stage values should be
shown as a short horizontal line at the estimated time
and date, and at the stage or elevation of the peak, and
identified as CSG or HWM.
For daily value discharge hydrographs, each instantaneous
peak discharge that is greater than the base discharge should be
plotted as a distinctive symbol on the day of occurrence. It
should be identified as PAB (peak above base). If peaks above
a base are not used for the gaging station, the annual peak
should be plotted. The user should have the option to specify a
temporary base level to be used only for plotting purposes.
11. Computation of Extremes
For most gaging stations, it is required that the maximum
peak stage and discharge, the secondary peak stages and dis-
charges, and the minimum discharge be computed for each
water year. The maximum peak stage and discharge, and the
minimum discharge, are referred to as the annual peak and
annual minimum. Guidelines for these computations are given
in sections 11.1 through 11.4.
11.1 Annual Peak Stage and Discharge
The annual peak stage and discharge are defined as the
highest instantaneous (unit value) gage height and discharge
associated with the highest flood peak that occurred during the
water year. The annual peak stage and discharge, and the asso-
ciated date and time, should be determined with the electronic
processing system. If the highest gage height and discharge was
at the beginning or end of the water year as a result of a reces-
sion from or rise to a peak that occurred in the previous or fol-
lowing water year, they should not be included as an extreme.
For some gaging stations, the user may designate that the max-
imum daily discharge be used rather than the maximum instan-
taneous discharge.
The annual instantaneous maximum gage height may
sometimes occur at a different time than the annual instanta-
neous maximum discharge. In these cases, the annual maximum
instantaneous discharge should be determined, and also the
gage height corresponding (at the same date and time) to this
discharge. In addition, the annual maximum instantaneous gage
height should be determined, and also the discharge corre-
sponding (at the same date and time) to this gage height. Dates
and times for both pairs of values should be determined.
11.2 Secondary Peak Stages and Discharges
Secondary peak stages and discharges are those peaks that
are less than the annual peak stage and discharge, but greater
than a specified base discharge. Furthermore, the secondary
peaks must conform to guidelines that insure their indepen-
dence. That is, to provide reasonable certainty that a peak has
not been influenced, or affected, by another peak. These guide-
lines are described by Novak (1985), and are given as follows.
“Two peaks are considered independent if the
hydrograph recedes to a well-defined trough between
the peaks. Publish both peaks if the instantaneous
discharge of the trough is equal to or less than 75
78 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
percent of the instantaneous discharge of the lower
peak; otherwise publish only the higher peak.
For small, highly responsive watersheds, only the
highest peak discharge resulting from an obvious
single storm event should be reported regardless of
the trough configuration or magnitude between
peaks.
For periods of diurnal peaks caused by snowmelt,
report only the highest peak during each distinct
period of melting, if such periods can be identified,
even though other peaks may meet the preceding cri-
teria. Identification of each distinct period of melting
is largely a matter of individual judgment, but the
principle as explained in paragraph 1 above for
instantaneous discharges can be applied to daily dis-
charges as an identification guide.”
All secondary peak stages and discharges should be deter-
mined with the electronic processing system. In addition, the
date and time for each secondary peak should be determined.
11.3 Annual Minimum Discharge
The annual minimum discharge is defined as the lowest
instantaneous (unit value) discharge that results during the
water year. For some gaging stations, the user may specify that
the lowest daily discharge be determined as the annual mini-
mum discharge. In either case, the electronic processing system
should determine the annual minimum discharge, and the asso-
ciated date and time (if applicable), for the water year.
11.4 Summary of Annual Extremes
A tabular listing of the annual peak gage height and dis-
charge, secondary peak gage heights and discharges, annual
minimum discharge, and all associated dates and times should
be produced with the electronic processing system. The user
should review this report on the system monitor, and select
items from it for publication and other applications.
12. Navigation Paths
This report describes the individual processes required for
the computation and analysis of gaging station records. A navi-
gation path, as described here, is a concept whereby the elec-
tronic processing system would lead the user through the pro-
cessing routines that are specific to the various gaging station
types. The user would be prompted for input and decisions
along the way, but much of the information transfer and record
processing would be automatic. As each processing step is com-
pleted, the electronic processing system automatically would go
to the next step defined for that particular gaging station type.
The electronic processing system tracks the progress through
the navigation path and can reinitiate processing at the point
necessary if processing is interrupted. In addition, when data are
entered and stored, those data automatically are transferred to
processing steps where they are needed. As an example, maxi-
mum stages entered from discharge measurement notes, crest-
stage gage notes, and highwater mark notes, automatically are
transferred to the verification and editing routines for unit
values of gage height so that recorded peak stages can be veri-
fied. A navigation path, combined with automatic information
transfer, increases the efficiency of record processing, removes
processes that are not needed for a specific type of station,
arranges the processing logically, reduces the need to manually
search for data and information, reduces the likelihood of
errors, and increases the probability that all relevant data and
information will be used.
12.1 Basic Navigation Path
Navigation paths for the various types of gaging stations
are similar in many, but not all, respects. The basic processing
steps required for a navigation path are shown in figure 12.
Some steps must be repeated for each parameter type, and some
steps will not apply for certain station types.The specific navi-
gation path for each station type should be derived from the
basic steps shown in figure 12.
The same basic steps shown above would be used for any
gaging station type, but with some modification. For instance,
an index velocity station would do steps 5 through 9 for the unit
values file of stage and the unit values file of index velocity.
The index velocity station also would require a shift analysis
and shift application (steps 10 and 11) for the index velocity-
mean velocity rating.
The choice of the correct navigation path to use for a spe-
cific gaging station should be automatic. When a gaging station
initially is created in the electronic processing system, the
method of processing (for example, stage-discharge, slope,
index-velocity, and others) is defined, which automatically
should establish the appropriate navigation path to use. Subse-
quent access to the processing routines for that station would
use that same navigation path. If the station is multi-purpose in
that various parameters are measured, such as streamflow,
water quality, and/or sediment, then the user would need to
specify the parameter that is to be processed so that the correct
navigation path is used.
12.2 Navigating Through a Navigation Path
The user should be allowed to enter a navigation path at
any point, as well as to back-track, if necessary. New data
would be entered by starting at the initial point of the navigation
path. If a period of record has not been completely processed,
the user should be able to start at the point where processing
ended during the prior processing session. Finally, the user
should be able to enter or back-track to a step in the navigation
path that already has been processed, and do a recomputation.
13. Estimating Missing Records 79
The electronic processing system should display a complete list
of the processing steps contained in the active navigation path,
showing the status of each for the period of record being pro-
cessed.
12.3 Auxiliary Processing Functions
Certain processing steps are not part of regular navigation
paths because they are not routine processes that are performed
each time a gaging station record is processed. These auxiliary
functions include preparation of station descriptions, station
analyses, and publication manuscripts. The functions also
include definition and analysis of rating curves, estimation of
missing records, computation of various statistics, quality-
assurance reports, and data archival. All of these functions are
described in other sections of this report.
13. Estimating Missing Records
Complete records of daily discharges, and other parame-
ters, are necessary in order to compute monthly and annual
totals and other statistics. Complete records also are needed to
compute total runoff from a drainage basin, to calibrate runoff
models, and to compute total monthly and annual chemical and
sediment loads. Data sometimes are missing because of instru-
ment failures and other reasons; thus, not permitting the normal
computation of daily records. Also, normal computation meth-
ods may not be applicable at all times, such as during backwater
from ice, debris, or other abnormal stream conditions. There-
fore, it is necessary to make estimates of discharge or other
hydrologic parameters for these periods of missing record.
The electronic processing system should allow the user to
estimate both unit values and daily values. However, estimation
of missing records should be kept to a minimum, and usually
should be limited to those parameters that will be published in
the USGS annual data reports and to those parameters that may
be required for the purpose of computing a published parame-
ter. For example, in some cases it may be reasonable to estimate
unit values of gage height for the purpose of computing daily
values of discharge, provided the gage heights can be estimated
with reasonable accuracy. The electronic processing system
should provide estimating methods that commonly are
accepted, but the user must be able to interact and apply unique
site specific information and procedures in order to make the
best estimate of missing records.
Also, it is important that only one estimate of discharge (or
other hydrologic parameter) be saved and archived. Although
the user may make various preliminary estimates for evaluation
and comparison purposes, only the best estimate should be
saved.
13.1 Estimating Discharge Records
A number of methods potentially are available to assist the
user in estimating discharge for periods of missing record. Six
such methods that can be adapted to computer application, are
described in sections13.1.1 through13.1.6. The electronic pro-
cessing system should allow the use of one or more of these
methods, as well as other site specific methods, to make and
compare discharge estimates.
13.1.1 Hydrographic and Climatic Comparison Method
The hydrographic and climatic comparison method, as
described by Rantz and others (1982), is the most common
method used to estimate discharge during periods of missing
record and ice-affected periods. A semilogarithmic hydrograph
of daily discharge is plotted, encompassing the period of miss-
ing record, and valid records for periods prior to and after the
missing record period. Other data and information, as shown
below, may be superimposed on this plot to aid in the estimation
procedure.
• Hydrographs of nearby stations (reference sites)
• Hydrographs based on the direct application of ice-
affected gage heights to the rating (without correction
for ice-induced backwater)
• Daily or hourly precipitation
Figure 12. Basic navigation path requirements.
Data entry
1. Discharge measurements
2. Crest-stage gage data
3. Highwater marks
4. Miscellaneous notes
5. Unit values
Verification and editing
6. Start/end dates and times
7. Define time corrections
8. Verify and edit
Computation and analysis
9. Define data (datum) correction
10. Perform shift analysis
11. Define shift curves and
application method
12. Primary computations
Review
13. User review
• Stage discharge
• Index velocity/
mean velocity
• Base stage or elevation
• Auxilliary stage
• Index velocity
80 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
• Daily temperature, and/or daily maximum and mini-
mum temperatures
• Discharge measurements
• Recession curves for station being estimated
• Notes and observations (for example, observed ice con-
ditions)
The electronic processing system should allow vertical and
horizontal repositioning of the hydrograph of the reference site
(or sites) until it corresponds as closely as possible to the avail-
able good record of the site to be estimated. When long periods
of missing record must be estimated, this repositioning process
may need to be performed various times, each time for a differ-
ent segment of the missing period. Values of daily mean dis-
charge are then estimated by using the reference site as a guide
and drawing a hydrograph for the missing period, whereas
taking into account all of the other available data and informa-
tion, such as the discharge measurements, climatic data, and
notes. This estimation process is performed by the user on the
electronic processing system monitor, using a mouse or other
suitable device. After the estimated hydrograph segment is
completed and accepted by the user, the electronic processing
system automatically should determine the daily values of dis-
charge, flag the values as estimated, and insert them into the
daily values file.
A period of missing record resulting during an unbroken
recession can be estimated by connecting the adjacent periods
of good record with a straight line or a smooth recession curve
on a semilogarithmic plot. This procedure is improved if reces-
sion curves, within the range of discharge to be estimated, are
available for the station in question to superimpose on the plot.
Recessions also may vary by season; therefore, it is useful to
categorize the recession curves by season of the year. The user
should be able to re-position the recession curves vertically and
horizontally to obtain the best fit of the recession curves. The
electronic processing system should allow for the storage, and
later recall, of recession curve data for this purpose.
13.1.2 Discharge Ratio Method
The discharge ratio method is used for estimating dis-
charge during ice-affected periods, and is described by Rantz
and others (1982). For this method, the equivalent open-water
daily mean discharge is multiplied by a variable correction fac-
tor, K, to produce a discharge corrected for the effects of back-
water from ice. The correction factor, K, is computed for each
discharge measurement as the ratio of measured discharge, Q
m
,
to the open water discharge, Q
r
. As changes occur in the ice
cover throughout a winter period, the value of K for each day
also will change, and intermediate values should be determined
with the electronic processing system by time interpolation
between K values determined from consecutive discharge mea-
surements. Climatic data, such as temperature and precipitation,
should be used to as a guide to modify the simple time interpo-
lation procedure, as necessary.
The computed correction factors, K, for each discharge
measurement should be displayed on a semilogarithmic plot,
along with the equivalent open-water daily discharge
hydrograph and the climatic data. The correction factor should
be merged with a value of 1.00 on the day prior to and the day
following each ice period. These dates are based on the
observed, or estimated, beginning and ending of ice cover.
Daily values files of the open-water discharge and the corre-
sponding correction factors, K, should be saved and archived
for all ice-affected periods.
13.1.3 Regression Method
Multiple, stepwise, regression is a useful method of relat-
ing time series discharge data of one gaging station to concur-
rent time series discharge data of one or more nearby reference
gages. Regression equations can be developed for specific
ranges of discharge, for instance, low flows, medium flows,
and/or high flows. They also can be developed for seasonal
periods and for ice-affected periods. The electronic processing
system should provide a flexible method of developing regres-
sion equations, allowing the user to specify reference gage
records, time periods, and discharge ranges. The regression
equations should include the ability to time-lag reference gage
records, and to use transformations of discharges (for example,
logarithmic). Also, developed regression equations and their
associated limitations, should be documented and archived for
later use, if desired.
A regression equation can be applied to provide estimated
discharges for periods of missing record. In addition, the same
regression equation should be used to compute discharge values
for short time periods adjacent to the estimated period where
discharges are known. These adjacent periods sometimes can be
used for verifying the accuracy of the regression results, and for
adjusting the estimated discharges during the period of missing
record to more closely fit the adjacent known records.
13.1.4 Water-Budget Method
A gaging station located just upstream from a reservoir, for
the purpose of measuring inflow to the reservoir, can have miss-
ing discharge records estimated using the water-budget method
if accurate records are available for the outflow from the reser-
voir and the change in contents of the reservoir. The daily
inflow to the reservoir is equal to the daily outflow plus or
minus the change in reservoir contents. In some cases, where
the flow at the inflow station may not represent the total inflow
to the reservoir, an adjustment may be required. The adjustment
may be simply the application of a drainage area ratio, or other
multiplication factor supplied by the user. The adjustment
factor can also be estimated by applying the water-budget equa-
tion during periods when inflow, outflow and storage records
are all available. The water-budget method is
, (32)
Q
i
KQ
o
(∆C )+=
13. Estimating Missing Records 81
where
Q
i
= flow at inflow gage,
Q
o
= outflow from reservoir,
K = inflow adjustment factor, and
∆C = change in contents of reservoir, computed as mid-
night contents on current day minus midnight content
on previous day.
The same principle can be used to estimate missing out-
flow records, for gaging stations located just downstream from
a reservoir. Equation 32 simply is rearranged to solve for out-
flow, Q
o
.
13.1.5 Mathematical Translation Method
The mathematical translation method is a set of various
mathematical functions that can be used to translate streamflow
records for other gaging stations (referred to as reference gages)
into estimates of streamflow for the gage.site where missing
records result. Some of these functions are similar to the regres-
sion method described in section13.1.3, but are defined inde-
pendently from regression methods. The selection of reference
gages to use for making an estimate is important because the
reference stations should be hydrologically related to the station
for which estimates are made. For this reason, reference stations
usually are nearby stations, have similar runoff characteristics,
and are sometimes stations on the same stream. The user should
use considerable care and judgment in selecting stations to use
with the mathematical translation method. This method
includes the following mathematical functions.
• Combining two streamflow records by addition, sub-
traction, multiplication, or division.
•Transforming a streamflow record into a different
record using
, (33)
where
Q
e
= estimated discharge,
Q
r
= discharge at reference gage, and
a, b, c, and d, are constants defined by the user.
•Offsetting a reference gage record by a specified time
period. The offset record can be mathematically com-
bined with another reference record, or can be trans-
formed by an equation. Two or more reference records
can be offset with the same, or different, offsets.
•Transformation of reference gage records into log10,
and inverse log10. These transformations can be made
prior to performing any of the above mathematical
functions.
13.1.6 Flow Routing Methods
Various flow routing models can be used to route a stream-
flow record from a reference gage to a downstream location on
the same stream, thereby providing an estimate of the flow at a
downstream gage site. However, these models are used external
to the electronic processing system, and the results must be
imported to the streamflow data base. Generally, it is not
expected that such models will be used very often for estimating
streamflow records because of the complex and intense efforts
needed for calibration and application.
13.2 Estimating Gage Height and Other Hydrologic
Parameters
Discharge is the primary parameter for most gaging sta-
tions, and discharge estimates usually are made for missing
periods so that a complete record is available for each year.
Complete records of other secondary, hydrologic parameters,
such as gage height or stream velocity, are not always required
and estimates are not usually made when missing records result.
However, in some cases estimates of these secondary parame-
ters are necessary.
Gage height (or elevation) can be reliably estimated only
for short periods of missing record, and even then, only when
gage-height changes are small during the period. Therefore, it is
recommended that gage-height (or elevation) records not be
estimated, unless specifically required for publication or for
computation of another parameter when no other reliable
method of estimating that parameter is available. For instance,
it usually is easier and more accurate to make direct estimates
of discharge than it is to estimate gage height for the purpose of
computing discharge.
When gage-height record must be estimated, subjective
judgment and interpolation between periods of good record
should be used. The user should use all available information,
such as miscellaneous gage readings, peak and minimum stage
information, and comparison with nearby gage sites to aid the
estimation process.
13.3 Comparison of Estimation Results
It is important that all estimated discharge records, and
other parameter estimates be compared with known records and
with estimates made by various methods for the same time
period. The best method of comparison is by plotting the
hydrograph that includes the estimated records. In this way the
estimated records can be compared visually to the observed
records on either side of the estimated period. Likewise, two or
more estimated records for the same period can be compared
visually for consistency and accuracy. The comparison proce-
dure should allow the user to make changes and revisions to the
estimated record as appropriate. Finally, the user should select
the best estimate for incorporation of the records into the data
base.
Q
e
ab+ Q
r
c+()
d
=
82 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
13.4 Flagging and Archival of Estimation Results
All estimated values of discharge and other hydrologic
parameters should be flagged in the data file as estimated. If
estimates are made by one or more of the named estimating pro-
cedures, this information automatically should be written to the
record processing notebook (see section15.1) for use in prepar-
ing the station analysis (section15.3). The estimated values and
the applicable flag should be archived with the observed data.
In some cases, where a parameter such as discharge is
computed from estimated values of another parameter, such as
gage height, the computed parameter should be flagged as
“computed from estimated values of _____.” The wording of
this flag should be varied to fit the situation.
14. Monthly and Annual Value
Computations
Monthly and annual values of stage, elevation, discharge,
runoff, reservoir contents, and tidal lows and highs should be
computed for each station as required or as designated. The
required and designated monthly and annual values will vary
with station type and with specific stations. All computations
of monthly values should be based on the rounded results of
daily values, and all computations of annual values should be
based on rounded results of either daily or monthly values, as
indicated. This results in consistent agreement of the daily,
monthly, and annual values.
At least two sets of annual values should be computed for
each gaging station, (1) for the calendar year, January through
December, and (2) for the water year, October through Septem-
ber. In special cases, the user may designate additional or alter-
native types of years, such as the climatic year, April through
March.
14.1 Monthly and Annual Values of Stage
Monthly and annual values of stage should be computed
for those stations where stage routinely is measured for defining
the gage-height fluctuations of a stream. For some stations, the
stage may be the primary end product, such as for a stage-only
station. In other instances the stage may be measured for the
purpose of computing other parameters, such as discharge.
The monthly stage values that should be computed are the
following.
• Monthly mean stage, in feet—The arithmetic mean of
all daily mean stages for each month.
• Monthly minimum daily stage, in feet—The lowest
daily mean stage for each month.
• Monthly maximum daily stage, in feet—The highest
daily mean stage for each month.
The annual stage values that should be computed are the
following.
• Annual mean stage, in feet—The arithmetic mean of all
daily mean stages for the water year and calendar year.
• Annual minimum daily stage, in feet—The lowest daily
mean stage for the water year and calendar year.
• Annual maximum daily stage, in feet—The highest
daily mean stage for the water year and calendar year.
14.2 Monthly and Annual Values of Discharge
Monthly and annual values of discharge should be com-
puted for gaging stations where daily discharge is routinely
computed, such as for a stage-discharge station, a slope station,
a velocity-index station, or other station types where stream-
flow is the parameter of primary interest. Some of the monthly
and annual values are required, whereas others are optional, and
are computed only for specific gaging stations. The optional
computations generally are designated on the basis of stream-
flow conditions, drainage basin size, natural runoff conditions,
degree of regulation, and other factors that may affect the
hydrologic value and need for the computed parameters.
The monthly discharge values that are required are the fol-
lowing.
• Monthly total discharge, in cubic feet per second-
days—Total of all daily mean discharges for each
month.
• Monthly mean discharge, in cubic feet per sec-
ond—The mean of all daily mean discharges for each
month, and is computed by dividing the monthly total
discharge by the number of days in the month.
• Monthly minimum daily discharge, in cubic feet per
second—The lowest daily mean discharge for each
month.
• Monthly maximum daily discharge, in cubic feet per
second—The highest daily mean discharge for each
month.
The monthly discharge values that are optional are as fol-
lows.
• Monthly runoff volume, in acre-feet—This is the
monthly total discharge, converted to a volume, in acre-
feet, and represents the total number of acres that would
be covered to a uniform depth of 1 ft by the total dis-
charge for that month. The monthly runoff volume, in
acre-feet, is computed by multiplying the monthly total
discharge, in cubic feet per second-days, times the con-
version constant, 1.983471.
• Monthly runoff depth, in inches—The monthly total
discharge volume, converted to a depth, in inches, that
would uniformly cover the drainage basin. The monthly
total runoff depth, in inches, is computed by multiply-
ing the monthly total discharge, in cubic feet per
14. Monthly and Annual Value Computations 83
second-days, times the conversion constant, 0.03719,
divided by the drainage area, in square miles.
• Monthly mean unit runoff, in cubic feet per second per
square mile—The monthly mean flow that would ema-
nate from 1 mi
2
of drainage area, if the flow were uni-
formly distributed throughout the drainage basin.
Monthly mean runoff, in cubic feet per second per
square mile, is computed by dividing the monthly mean
discharge, in cubic feet per second, by the drainage
area, in square miles.
The annual discharge values that are required are as fol-
lows.
• Annual total discharge, in cubic feet per second-
days—The total of all daily mean discharges for the
year.
• Annual mean discharge, in cubic feet per second—The
mean of all daily mean discharges for the year, and is
computed by dividing the annual total discharge by
365, or by 366 for leap years.
• Annual minimum daily discharge, in cubic feet per sec-
ond—The lowest daily mean discharge for the year.
• Annual maximum daily discharge, in cubic feet per sec-
ond—The highest daily mean discharge for the year.
The annual discharge values that are optional are as fol-
lows.
• Annual runoff volume, in acre-feet—The annual total
runoff volume, in acre-feet, is computed by summing
the monthly values of runoff volume for the year.
• Annual runoff depth, in inches—The annual total
runoff depth, in inches, is computed by summing the
monthly values of runoff depth for the year.
• Annual mean unit runoff, in cubic feet per second per
square mile—The annual mean runoff, in cubic feet per
second per square mile, is computed by dividing the
annual mean discharge, in cubic feet per second, by the
drainage area, in square miles.
14.3 Monthly and Annual Values for Reservoirs
The computation of monthly and annual values for reser-
voir stations is varied and highly dependent on the type of daily
values that are used for the station. Reservoir stations may
require daily mean elevations, daily mean contents, elevation at
a specific time (for example, at 0800, 1200, 2400, or other
time), or contents at a specific time. The choice of daily values
that are used, and published, for a reservoir station is dependent
on user requirements, and consequently, the monthly values
that should be computed will be based on these same require-
ments. The list of monthly and annual values that can be com-
puted is fairly long (see below), but generally only a few of
these values will be chosen for a given reservoir station. The
choice will be partially based on the daily values used for the
station, and partly on other considerations that relate to the
anticipated use of the monthly and annual values.
The monthly reservoir values that may be computed are as
follows.
• Monthly minimum value—The lowest value during the
month of one or more of the following parameters:
• daily mean gage height
• daily mean elevation
• daily mean contents
• daily maximum gage height
• daily maximum elevation
• daily maximum contents
• daily minimum gage height
• daily minimum elevation
• daily minimum contents
• daily gage height at a specified time
• daily elevation at a specified time
• daily contents at a specified time
The full parameter name is formed by preceding the
selected name(s) by “monthly minimum”; for example,
“monthly minimum daily maximum elevation.”
• Monthly maximum value—The highest value during
the month of selected parameters. The possible choices
are the same as listed above for monthly minimum val-
ues, and the full parameter name is formed as explained
above.
• Monthly mean value—The mean of all daily values
during the month of one or more of the following
parameters:
• daily mean gage height
• daily mean elevation
• daily mean contents
The full parameter name is simply monthly mean gage
height, elevation, or contents.
• End of month contents—The reservoir contents at time
2400 hours of the last day of the month.
• Monthly change in contents—The change in reservoir
contents during the month. It is computed by subtract-
ing the end of month contents for the previous month
from the end of month contents for the current month.
The change in contents may be shown in units of acre
feet, cubic feet, or in units of equivalent cubic feet per
second, or all three. Equivalent cubic feet per second is
computed by dividing the change in contents, in cubic
feet, by the number of seconds in the month.
The annual reservoir values that may be computed as fol-
lows.
84 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
• Annual Minimum value—The lowest value during the
year of selected parameters. The possible choices are
the same as listed above for monthly minimum values.
• Annual maximum value—The highest value during the
year of selected parameters. The possible parameters
are the same as listed above for monthly minimum val-
ues.
• Annual mean value—The mean of all daily values of
selected parameters during the year. The possible
parameters are the same as listed above for monthly
mean values.
• End of year contents—The reservoir contents at time
2400 hours of the last day of the year.
• Yearly change in contents—The change in reservoir
contents during the year. It is computed by subtracting
the end of year contents for the previous year from the
end of year contents for the current year. The change in
contents may be shown in units of acre feet, cubic feet,
or in units of equivalent cubic feet per second, or all
three. Equivalent cubic feet per second is computed by
dividing the change in contents, in cubic feet, by the
number of seconds in the year.
14.4 Monthly and Annual Values for Tidal Stations
Tidal stations require the computation of various monthly
and annual values as described below. For tidal stations that use
an arbitrary gage-height datum and a datum-conversion con-
stant to convert the gage heights to NGVD, the monthly and
annual values should be computed for both datums.
The monthly tide values that may be computed as follows.
• Monthly mean stage and/or elevation, in feet—The
mean of all daily mean stages and/or elevations for each
month.
• Monthly mean high tide, in feet—The mean of all daily
HIGH-HIGH tide stages and/or elevations for each
month.
• Monthly mean low tide, in feet—The mean of all daily
LOW-LOW tide stages and/or elevations for each
month.
• Monthly minimum low tide, in feet—The lowest of all
daily LOW-LOW tide stages and (or) elevations for
each month.
• Monthly maximum high tide, in feet—The highest of all
daily HIGH-HIGH tide stages and (or) elevations for
each month.
The annual tide values that may be computed as follows.
• Annual mean stage and/or elevation, in feet—The
mean of all daily mean stages and (or) elevations for the
year.
• Annual mean high tide, in feet—The mean of all daily
HIGH-HIGH tide stages and/or elevations for the year.
• Annual mean low tide, in feet—The mean of all daily
LOW-LOW tide stages and/or elevations for the year.
• Annual minimum low tide, in feet—The lowest of all
daily LOW-LOW tide stages and/or elevations for the
year.
• Annual maximum high tide, in feet—The highest of all
daily HIGH-HIGH tide stages and/or elevations for the
year.
15. Documents
The operation and maintenance of gaging stations, and the
analysis and publication of gaging station records, requires a
number of documents to describe each gage and to document
the records for that gage. In an automated electronic processing
system these documents can be easily prepared using prescribed
formats, automatic transfer of information, and a word-process-
ing system. Four basic documents, (1) record processing note-
book, (2) station description, (3) station analysis, and (4) station
manuscript should be incorporated and formatted for each sur-
face-water record. Additional, miscellaneous documents, such
as the documentation of an indirect measurement, can be pre-
pared, as needed, using the word-processing system.
15.1 Record Processing Notebook
The record processing notebook is an open comment file
that can be accessed at any point during the processing of a
gaging station record. The notebook provides the user a place to
record comments pertaining to the data and information, the
reasoning for various analytical steps such as shifts, data correc-
tions, rating changes, and others, and other information that
should be retained for future use. One of the main uses for the
notebook is the preparation of the annual station analysis
(described in section15.3) where it will allow quick and easy
recall of the analytical steps used during the preceding year. All
comments recorded in the notebook automatically should be
categorized into defined subjects, patterned primarily according
to the format of the station analysis. In addition, all comments
should be dated automatically according to the date of entry,
and automatically signed with the name of the user making the
entry. All processing steps should fit into one of the comment
categories listed below.
• Equipment—All comments pertaining to field equip-
ment such as recorders, gage structures, artificial con-
trols, cableways, and other field measuring devices
should be saved as an equipment category. Most com-
ments in this category will be derived from field notes
such as discharge measurements, level notes, crest-
stage gage notes, and miscellaneous notes.
• Unit values data—All comments pertaining to unit
values of gage height, elevation, index velocity, and
other unit values field data should be saved in this cate-
15. Documents 85
gory. These comments generally will relate to the com-
pleteness and accuracy of the input unit values files, and
will include information such as periods of missing
record, reasons for missing record, substitute record,
estimated record, time corrections, and others. Most
comments for this category will be derived during the
entry, verification, and editing of unit values files.
• Unit values data corrections—Comments in this cate-
gory will relate to unit values data corrections, includ-
ing datum corrections resulting from gage leveling.
These comments should describe any gage problems
that caused erroneous (but correctable) unit values to be
recorded, the method of making corrections, and
changes in gage datum. Most comments for this cate-
gory will come from the parameter value corrections
processing step and the gage datum analysis step.
• Rating analysis—Comments in this category will relate
to all phases of rating analysis, including the develop-
ment of new ratings, revision of old ratings, use of
cross-section data to define ratings, control conditions,
shift analysis, shift application, rating curve plots, shift
curve plots, and any other aspect of rating curve analy-
sis.
• Discharge computations—Comments in this category
will relate to the methods of producing unit and daily
discharge records. These comments will include meth-
ods of direct computation and methods of estimating
record during periods of missing record, ice, backwater,
and other conditions. Comments for this category
should be derived during the primary computation
phase and missing record estimation phase of record
processing.
• Quality assurance and accuracy—Comments in this
category will relate to any phase of record processing
that provides special applications of quality control and
quality assurance. Comments also should be included
for any condition that may affect the accuracy of the
records. Comments for this category may be derived at
any point during the process of producing a streamflow
record from the initial entry of field data through the
final computation steps.
• Miscellaneous—Comments in this category will be
miscellaneous comments that do not fit in any of the
other categories.
15.2 Station Descriptions
The station description is a narrative of the features and
characteristics of a gaging station. A basic format containing
specified topics is used for most station descriptions; however,
deviations from the basic format sometimes are needed to
describe special gaging station installations. Most of the input
for preparing or editing a station description is supplied by the
user. Some items, however, should be supplied automatically
from other parts of the electronic processing system. For
instance, when new elevations of reference marks, benchmarks,
and other gage features are entered in the electronic processing
system, these elevations automatically should be transferred to
the station description. Other automatic transfers should be
made, as appropriate.
A complete station description usually is prepared when a
new gaging station is established. The date of preparation, and
the name of the preparer automatically should be attached to a
new station description. After the station description is com-
pleted, generally it will not require complete rewriting for many
years, unless there is a major change in the gaging station. How-
ever, minor changes or changes to one or two features of a sta-
tion may occur from time to time, and the station description
should be edited to reflect these changes. The electronic pro-
cessing system should provide an easy and flexible method for
making such changes. In addition, the date of editing, and the
name of the person making the change, automatically should be
attached to each change. Automatic updating, made with the
electronic processing system, should be footnoted as such.
The following items are suggested for most station
descriptions; however, some of these may not apply to a spe-
cific gaging station and should not be used. On the other hand,
additional items may be required for some gaging stations.
Also, some stations (such as slope stations) may have auxiliary
gages and will require multiple entries for some items. See
Kennedy (1983) for additional details.
• Station name
• Station ID
• Location and road log
• Establishment
• Drainage area
• Gage
• History
• Reference and benchmarks
• Channel and control
• Discharge measurements
• Floods
• Gage height of zero flow
•Winter flow
•Regulation and diversions
• Accuracy
• Cooperation
• Purpose of record and gage classification
• Land ownership
• Indirect measurement site
•Sketch
• Photographs
• Observer
86 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
15.3 Station Analyses
The station analysis is a narrative description of the meth-
ods used to analyze the gaging station records for a water year.
The analysis includes information about station equipment, per-
formance of the gage and related equipment, the rating, shifting
control methods, computation of discharge, accuracy, and any
other information about how the station records were produced.
The station analysis is one of the most important documents
produced for each year of gaging station records because it is
the primary documentation for quality assurance and quality
control of these records.
The station analysis for a gaging station usually is written
and finalized at the end of each water year, however, parts of it
may be written at any time during the year as information
becomes available. The record processing notebook described
in section 15.1 should be utilized to the fullest extent as an aid
in writing the station analysis. The electronic processing system
automatically should transfer information from the record pro-
cessing notebook to the appropriate paragraphs of the station
analysis.
The electronic processing system also should automati-
cally transfer information from other parts of the electronic pro-
cessing system to the station analysis phase to assist the user.
Specific transfer items should include the following.
•Level and datum information should be transferred
from the most recent level summary. This information
should include the date of the latest levels, and informa-
tion about datum differences of the various gages at the
station.
• All periods (dates) of missing record, and the total
number of days of missing record, should be trans-
ferred from the unit values files.
• The minimum and maximum gage heights recorded
during the water year should be transferred from the
unit values files.
• The number of discharge measurements made during
the water year, and their corresponding sequence num-
bers, should be transferred from the measurement file.
In addition, the lowest and highest measured gage
height and discharge should be transferred from the
measurement file.
• The comparison of measured discharges to computed
unit values of discharge should be transferred from the
table described in section 9.3.5.
•Methods of estimating missing records and ice records
should be transferred from the electronic processing
system documentation of estimating missing records
for the water year.
• The listing of records used for hydrograph comparisons
should be transferred from the electronic processing
system documentation of hydrograph comparisons
used for the water year. This listing should include sta-
tion names, parameters compared, and periods of
record compared.
• The sequence numbers for the rating curves and the
shift curves used during the water year should be trans-
ferred from the rating curve file and the shift curve file.
•Any information relative to quality control should be
transferred from field notes, record processing note-
book, and comment files that have been documented in
the electronic processing system.
The transferred information, both from the record process-
ing notebook and the various other parts of the electronic pro-
cessing system, then can be used to write the station analysis.
The station analysis should include, at a minimum, the follow-
ing items and paragraphs. For some gaging stations, other para-
graphs may be required in order to adequately describe the com-
putation methods. See Kennedy (1983) for additional details.
• Station name
• Station ID
•Water year
• Equipment
• Gage-height record
• Gage-height and datum corrections
• Rating
• Discharge
• Quality assurance and control
• Remarks
• Recommendations
The name of the user who writes the station analysis, and
the date of preparation, automatically should be attached to the
end of the station analysis. Also, the name of the reviewer (see
section 16) automatically should be attached, along with the
date of review completion.
15.4 Station Manuscripts
The station manuscript is the narrative part of the pub-
lished page for each gaging station record for each water year.
A standard format is used that consists of paragraphs, as
required, taken from the following list.
•A heading consisting of the basin name, station num-
ber, and station name
• Location
• Drainage area
• Period of record
•Revised records
• Gage
• Remarks (includes statement on accuracy)
• Cooperation
16. Review, Approval, and Finalization of Records 87
• Extremes for period of record
• Extremes outside the period of record
• Extremes for current year
•Revisions
The station manuscript is combined with the table of daily,
monthly, and annual values to form the final publication page
for each gaging station. In addition, a number of statistics are
determined for the current water year, the current calendar year,
and the period of record. These statistics are arranged in such a
way as to provide a comparative presentation of data for the
gaging station. For some stations, multiple statistical summaries
are included, such as separate summaries before and after regu-
lation by a major reservoir. The final station manuscript is vari-
able among gaging stations depending on the period of record,
the parameter of interest, the statistical presentation, and other
characteristics of each individual station. For details of station
manuscript preparation, see Novak (1985).
A copy of the previous year's manuscript (if available)
should be recalled for use as a guide and starting point for the
preparation of the current year's manuscript. Information used
for completion of some parts of the station manuscript automat-
ically should be computed and transferred from other parts of
the electronic processing system. The electronic processing
system automatically should highlight any differences of infor-
mation between the previous and the current manuscript.
16. Review, Approval, and Finalization of
Records
Gaging station records are reviewed at various points
during the process of entering, analyzing, interpreting, and
computing the streamflow information. These records generally
are referred to as working reviews that usually are made by the
user as the records are processed. This report refers to a number
of places during the process of producing a streamflow record
where such reviews should be made. Working reviews are a
normal function of the record production process, and the elec-
tronic processing system provides the user with numerous aids
to make this process as easy as possible.
A formal review should be made after the records have
been processed and the user is satisfied that the records are com-
plete and accurate. This final review should be made by a senior
reviewer who is designated to make such reviews. This review
ultimately results in the approval and finalization of the records
for publication and archival if the reviewer finds that the records
are complete and accurate. If this review reveals deficiencies in
the records, the reviewer can return the records to working
status (see section 17.2).
The formal review should have access to all of the same
review functions that are used in the record processing steps.
These review functions would include all output tables, such as
the discharge measurement summary tables, the level summary
tables, the unit values tables, the primary computation tables,
the diagnostics tables, the daily values tables, and any other
table produced during the record processing. Of even greater
importance, the final reviewer should have easy access to
graphs such as the rating curves, shift curves, unit values hydro-
graphs, and daily values hydrographs. The reviewer also should
have access to the comments file and should be allowed to enter
comments. If a station analysis has been prepared, the reviewer
should be allowed to review and edit, as appropriate.
When the review is complete and the records are consid-
ered acceptable and accurate, they should be designated as
approved. The electronic processing system should flag the
records as approved and ready for publication and archiving.
Records that are flagged as approved should be protected from
any further changes or revisions. In the event that a change to an
approved record is required, the records must be set back to
working status (see section 17.2).
17. Status of Data and Information
All data and information will progress through a hiearchy
of processing steps. These steps include (1) original data, (2)
working data, (3) review, (4) approval, and (5) publication. Spe-
cific processing functions that pertain to each of these steps
have been described in previous parts of this report. The status
of the data and information as they progress through these steps
are described in sections 17.1 through 17.5.
17.1 Original Data
Original data are defined as direct measurements of a field
parameter such as gage height, velocity, depth, width, or other
station variable. Direct field measurements are considered to be
those made by the hydrographer while at the gage site. These
include all measurements required to make a streamflow mea-
surement, direct visual readings of gages, determinations of
highwater marks and crest-stage gage readings, leveling data,
and other data collected during the course of servicing the gage.
Historically, these notes and measurements were recorded on
paper field notes. Presently (2002), paper field notes are the
accepted media by the USGS. Paper field notes are considered
the original data, and should be preserved even though much of
the data and information from these notes will be entered man-
ually to the electronic processing system.
Electronic field notebooks presently are in the early oper-
ational stages for the purpose of recording direct field measure-
ments. It is expected that these notebooks will be used exten-
sively within the next 5 to 10 years, and may eliminate the need
for some or all of the paper note recording. All field measure-
ments recorded in electronic format should be electronically
transferred to the electronic processing system. The first trans-
fer of this type becomes the original data and should be pre-
served without alteration. Any supplemental paper field notes
should be preserved separately as original data.
88 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
In addition to direct field measurements made by the
hydrographer, most gaging stations have automatic recorders to
continuously, or intermittently, record gage height, velocity, or
other parameters. Some gages contain two automatic recorders
that record duplicate data. Frequently, one recorder is desig-
nated the primary recorder and the second recorder is desig-
nated as a backup recorder. Data from the primary recorder
should be considered the primary original data. Data from the
backup recorder also are original data, but should be used only
for filling in missing or erroneous periods of the primary record.
The process of filling periods of missing data should not be per-
formed on the original records, but should be done on the work-
ing records. Both the primary and backup original unaltered
data should be set aside for archiving.
Various types of automatic field recorders are currently in
use by the USGS, each having unique characteristics that relate
to the definition of original data, as well as to the format and
method by which the data will be preserved. The following text
describe these characteristics.
• Analog recorders—Analog recorders are graphical
recorders that record a pencil or pen trace on a paper
chart. This chart is the original record and should be
preserved. Various mechanical and electronic methods
are available that can be used to digitize the graphical
record into an electronic record suitable for entry to the
electronic processing system. The digitized record is
not considered an original record, and should be used
only as a working record (see section 17.2 for a defini-
tion of working data).
• Automated digital recorders—Automated digital
recorders record data as punched holes in a paper tape.
These tapes cannot be read easily by eye, and usually
are translated into an electronic format by paper tape
readers. The first electronic unaltered translation of the
tape is considered the original record and should be per-
manently preserved.
• Electronic data loggers—Electronic data loggers
record data in various formats that must frequently be
translated to engineering units through the use of spe-
cial algorithms. The first translation to engineering
units is considered to be the original record and should
be preserved as such.
• Data-collection platforms—Data-collection platforms
are systems whereby data are transmitted from the field
site to an office by radio, telephone, or satellite. In addi-
tion, the data frequently are recorded at the field site by
a data logger or other backup recorder. The primary
original record may be either the field recorded data or
the transmitted data, depending on the individual gage
setup, or the specific policy of the office collecting the
data. In either case, the designated primary original
data and the designated backup record should be pre-
served.
All original data that are entered to the electronic process-
ing system should be preserved unaltered with the electronic
processing system, and should be set aside for permanent
archiving. A duplicate copy of the original data files should be
made for the working files.
17.2 Working Data
Copies of original data files are put into a status of working
data. Working data files are processed with the electronic pro-
cessing system based on prescribed computation routines and
by interactive input by the user. Data and information in the
working status generally follow a specific navigation path (see
section 12) of transformations and computations that ultimately
result in a record of discharge, reservoir contents, or other
parameter that is published or used for various project work.
While in the working status, data and information may be
changed as deemed appropriate by the user, reworked if neces-
sary at any point in the working process, and even completely
deleted so that processing can be restarted. At some point, how-
ever, when the user is satisfied that the computations are com-
plete and accurate, the working files are moved to a review sta-
tus. At this point, changes can no longer be made unless the data
files are moved back to working status at the direction of a des-
ignated reviewer.
17.3 Review
The process of review has been described in section 16.
Review status is the point where a senior reviewer reviews the
records and either accepts the records and recommends them for
approval, or rejects the records and recommends a complete or
partial reworking. Records that are in the review status may not
be changed or altered in any way. If the review reveals the need
for changes, the records must be moved back to working status
as described in section 17.2.
17.4 Approval
The approval status is the step following review, and
results from the final approval of records as described in section
17.3. Records that are approved are considered ready for publi-
cation.
17.5 Publication
The publication status refers to records that are published
in USGS annual data reports, released as approved records for
public access, or released for public use in an electronic media
such as CD ROM or the World Wide Web. Published records
may be revised, but the original published values must be
retained and flagged as superseded. The new, revised values
must be flagged as revised. Revisions to approved and pub-
18. Archiving 89
lished records must follow USGS guidelines for publication
(Novak, 1985) of water-resources data.
18. Archiving
Data archiving is a complex subject that deals with the per-
manent retention, protection, and accessibility of original
records, and other records that support published scientific stud-
ies and analyses. With the advent of electronic media for collec-
tion and analysis of hydrologic data and information, it has
become increasingly difficult to define the method by which
these records should be archived. A study group in the early
1990's addressed the problems of data archiving, and made rec-
ommendations that are given by Hubbard (1992). That report
provides a comprehensive set of recommendations for the man-
agement and retention (archiving) of hydrologic data, both for
hard copy and electronic data and information, and should be
used as the basis for permanent archiving of all hydrologic data
and information. Only a brief summary of the archiving recom-
mendations for electronic data and information will be given
here, as taken from Hubbard (1992).
The following list of electronic data and information is not
all inclusive, but at a minimum these items should be placed in
permanent electronic archives.
• All original data for automated data-collection sites, as
defined in section17.1.
• Records of algorithms used to convert field values to
conventional engineering units.
• All non-automated data collected in electronic format,
such as discharge measurement notes, as defined in sec-
tion 4.2.
• All approved files of edited and calculated data, such as
unit values and daily values of gage height, velocity,
correction values, shift adjustments, discharge, reser-
voir contents, and other parameters resulting from the
processing of the gaging station records.
• All approved algorithms, rating curves, shift curves,
and other transformation information required for the
processing of the records.
• All documents specific to a gaging station, such as sta-
tion descriptions, station analyses, station manuscripts,
level summaries, and comment files.
19. Quality Assurance and Quality Control
Quality assurance and quality control (QA/QC) is the pro-
cess of performing specific tasks that ensure that the input data,
algorithms, transformations, computations, and final results are
complete and accurate to the greatest extent possible. Much of
the QA/QC process is automatic in that many arithmetic checks,
cross checks, and logic checks are programmed into the elec-
tronic processing system software. When inconsistencies are
found in field data, computed records, or other parts of the
records, the electronic processing system alerts the user so that
appropriate changes can be made. These automatic checking
routines have been defined and explained in various sections of
this report, but primarily in sections 5 and 6. In addition to the
automatic QA/QC checking, the electronic processing system
provides a number of places where the user or supervisor can
review and compare the computations and final results. All of
these tasks, both automatic and manual, are important to the
quality-assurance and quality-control process.
In addition to the actual checking and review process, it
equally is important that the QA/QC process and findings be
documented. For streamflow and other surface-water gaging
stations, the documentation traditionally has been known as an
annual station analysis. The preparation of a station analysis is
described in section 15.3. Automation and electronic processing
provides an easy and efficient means by which data and infor-
mation can be supplied to the writer of the station analysis. A
number of different reports and information items that can be
used for this purpose are described in the station analysis sec-
tion (15.3). Some of these reports may be useful as QA/QC doc-
umentation.
In summary, the quality-assurance and quality-control pro-
cess is a continuous process that starts when data are collected
in the field, and continues throughout the data and information
processing procedure. This section of the report does not define
specific QA/QC tasks because these are imbedded within each
of the many steps required to produce a surface-water record.
20. Summary
The USGS has been using automated data-processing
methods in various electronic systems to process surface-water
records since about 1963. This report describes standards for
the processing, computation, and analysis of streamflow
records using modern electronic computer methods. The tradi-
tional USGS methodology for streamflow data collection and
analysis has been incorporated into these standards to the great-
est extent possible. Although these standards are intended for
use primarily by the USGS, they may be used by other organi-
zations doing similar work. In addition, the high speed and ver-
satility of present-day computers allow for the design of an elec-
tronic processing system that offers many new opportunities to
expand and improve on the ways that some traditional USGS
methods have been applied.
Surface-water data and surface-water information are
defined for this report to distinguish between a variable that is
measured and cannot be repeated (data), and a variable that is
computed or changed in some way (information). For example,
a measurement of gage height or a measurement of depth are
considered data. Whereas, a computed value of discharge or
cross-section area is considered information. The term unit
value is defined as data or information that is associated with a
90 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
specified time and date, and usually is part of a time-series.
Daily values are data or information that is associated with a
specific date, and the time of the daily value usually is not
required.
One of the first steps for use of the electronic processing
system is the entry of data and information. Unit values of data
are obtained from various sources such as observer data, analog
recorders, automated digital recorders, electronic data loggers
and data-collection platforms. The time system for unit values
is important, and is usually based on local time, which includes
standard and daylight savings time. However, the electronic
processing system should provide the capability to transform
and store all times in Universal Coordinated Time (UTC). Field
measurement data and information, such as discharge measure-
ments, gage datum leveling, crest-stage gage data, and cross-
section data also must be entered to the electronic processing
system. These data and information may require manual entry
from paper field notes or from electronic field notebooks.
All unit values entered to the electronic processing system
should be verified and edited, if necessary. However, an elec-
tronic copy of the original values should be archived, and all
data processing should be performed on a copy of the original
values. Times and dates should be verified, and corrections and
adjustments made, as necessary, to account for clock errors.
UTC adjustments should be made following the time and date
corrections. Parameter values, such as gage height, should be
verified by making various comparisons such as threshold com-
parisons, rating-curve comparisons, direct-reading compari-
sons, and graphical comparisons. Corrections to parameter
values should be made for any datum or instrument errors that
may have occurred.
Field measurement data and information that are entered to
the electronic processing system require various checks to
verify correctness. Some field measurements also require spe-
cial analyses for use in other parts of the electronic processing
system. Discharge measurements should be checked for arith-
metic errors, and for logic and consistency. The standard error
of discharge measurements should be computed if applicable
methods can be used. Shift analysis should be made according
to the methods defined for stage-discharge ratings, slope rat-
ings, rate-of-change-in-stage ratings, and velocity-index rat-
ings. Special procedures for verification and analysis apply to
some measurements, such as ice measurements, measurements
with vertical angles, moving boat measurements, acoustic Dop-
pler current profiler measurements, indirect measurements,
weir and flume measurements, tracer-dilution measurements,
volumetric measurements, and discharge estimates. Specific
rounding and significant figures are defined for all discharge
measurements.
Rating curves are an integral part of the computation of
most streamflow records. The electronic processing system
should accommodate the use of various rating curve types,
including stage-discharge, stage-area, velocity-index, stage-
velocity factor, stage-fall, fall ratio and discharge, stage-1/US
c
,
and elevation-reservoir contents. In addition, control structures
require a number of different rating curves and equations. Rat-
ings should be entered as tabular, graphical, or equations, and
should be either linear or logarithmic. Scale offsets are an inte-
gral part of most logarithmic ratings, and the electronic process-
ing system should provide flexibility in entering multiple scale
offsets, and in computation of best scale offset.The user should
be allowed to enter, draw, shape, and edit rating curves directly
on the electronic monitor to avoid the time-consuming hand
plotting and drawing of ratings. Finally, the electronic process-
ing system should provide various rating development proce-
dures based on stream hydraulics.
Stream channels change at times because of natural or
manmade influences. For this reason, certain ratings may
require temporary adjustments, called shift corrections. The rat-
ings to which shifts may be applied are stage-discharge and
velocity-index. All other ratings should be redrawn.
Primary computations are the functions that convert input
data, such as gage height or velocity data into unit, daily
monthly, and annual values of discharge or other output param-
eters.This part of the process should be carried out by the elec-
tronic processing system with minimal user interaction. It
should produce tables, graphs, and files of information that
commonly are referred to as primary output. Each station type
has a specific primary computation process that produces spe-
cific information. However, the primary output for most gaging
stations is to calculate stream discharge (unit, daily, monthly,
and annual values) and some related information such as stage
or velocity. Primary computations for reservoir stations pro-
duce reservoir elevation and contents. Primary computations
for tide stations produce various tidal statistics such as high and
low tide elevations.
Other functions that the electronic processing system
should provide to the user include hydrograph plotting for both
daily and unit values, and automatic determination of extreme
values such as maximum and minimum stages and discharges
for a water year and calendar year. The electronic processing
system should provide navigation paths that guide the user
through routine computation and analysis of the streamflow
records for the various gage types. In order to produce complete
records of daily streamflow and other parameters, estimating
methods such as the hydrograph and climatic comparison
method, discharge-ratio method, regression method, water-
budget method, mathematical translation method, and the flow
routing method are functions of the electronic processing sys-
tem.
Various monthly and annual statistics should be computed
for streamflow stations, reservoir stations, and tide sta-
tions.These statistics should conform to the traditional statistics
that currently are published in USGS annual data reports. The
electronic processing system should provide the user a place to
enter and archive documents such as the record processing note-
book, station descriptions, station analyses, and station manu-
scripts. Quality assurance and control should be a continuous
process in the electroic processing system from data collection
to archiving. Finally, the electronic processing system should
allow easy access to the computed records for review, approval,
finalization, and archiving.
21. References 91
21. References
Collins, D.L., 1977, Computation of records of streamflow at
control structures: U.S. Geological Survey Water-Resources
Investigations Report 77–8, 57 p.
Corbett, D.M., and others, 1943, Stream-gaging procedures:
U.S. Geological Survey Water-Supply Paper 888, 245 p.
Dalrymple, Tate, and Benson, M.A., 1967, Measurement of
peak discharge by the slope-area method: U.S. Geological
Survey Techniques of Water-Resources Investigation, book
3, chap. A2, 12 p.
Dempster, George R., Jr., National water information system
user’s manual, v. 2, chap. 3, Automated data processing sys-
tem: U.S. Geological Survey Open-File Report 90–116.
Fulford, J.M. (1993), User’s guide to hydraulic information
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at Stennis Space Center, MS 39529.
Hubbard, E.F., 1992, Policy recommendations for management
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Hutchison, N.E., and others, 1977, WATSTORE user's guide,
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Report 77–729–I, 230 p.
Johnson, L.H., 1952, Nomography and empirical equations:
New York, John Wiley, 150 p.
Kennedy, E.J., 1983, Computations of continuous records of
streamflow: U.S. Geological Survey Techniques of Water-
Resources Investigation Report, book 3, chap. A13, 53 p.
Kennedy, E.J., 1984, Discharge ratings at gaging stations: U.S.
Geological Survey Techniques of Water-Resources Investi-
gation Report, book 3, chap. A10, 59 p.
Kennedy, E.J., 1990, Levels at streamflow gaging stations: U.S.
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gation Report, book 3, chap. A19, 31 p.
Novak, C.E., 1985, WRD data reports preparation guide: U.S.
Geological Survey Open-File Report 85–480, 199 p.
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streamflow: v. 1 and 2, U.S. Geological Survey Water-
Supply Paper 2175, 631 p.
Sauer, V.B., and Meyer, R.W., 1992, Determination of error in
individual discharge measurements: U.S. Geological Survey
Open-File Report 92–144, 21 p.
Schaffrannek, R.W., Baltzer, R.A., and Goldberg, D.E., 1981,
A model for simulation of flow in singular and intercon-
nected channels: U.S. Geological Survey Techniques of
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110 p.
Shearman, J.O., 1990, User's manual for WSPRO—A computer
model for water surface profile computa tions: Federal High-
way Administration Publication No. FHWA–IP–89–027,
177 p.
92 Standards for the Analysis and Processing of Surface-Water Data and Information Using Electronic Methods
