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OSW Hydroacoustics

Documentation of Ratings for Index-Velocity Streamgages--Examples

The Office of Surface Water (OSW) has issued policy on the minimum required documentation for stage-area ratings and index-velocity ratings at index-velocity gages operated by the USGS in OSW Technical Memo 2015.05. The purpose of these pages is to provide examples of how to implement this policy for different kinds of data and analyses.

Stage-Area Ratings

A stage-area rating is mechanism for computing the cross-sectional area for a channel for a given stage. The stage-area rating is developed for a fixed cross-section in the stream (the standard cross-section). The standard cross section is a cross section near to the ADVM that is chosen for the development of the stage-area rating and which can be re-surveyed at regular intervals. The steps for development of the stage-area rating are given in Levesque and Oberg (2012 p. 29-34).

Development and validation of the stage-area rating is an essential part of the process for computing index-velocity records. Presently (2015), the USGS uses the AreaComp2 software to develop stage-area ratings.

Table summarizing the requirements for documenting stage-area ratings

Example Stage-Area Rating Documentation and Data

Text file output from AreaComp2
NWIS rating table output
Stage-area rating verification documentation

Index-Velocity Ratings

A index-velocity rating is tool for computing an estimate of the mean water velocity in a channel using water velocity measured in some portion of that channel as an index or predictor of the mean velocity in the channel. Graphical and statistical analyses are used to develop an appropriate index rating. The flowchart prepared by Levesque and Oberg (2012) illustrates the approach used to develop index-velocity ratings in the USGS.

Table summarizing the requirements for documenting index-velocity ratings

Examples of Index-Velocity Rating Documentation

Discharge measurement summary table
Graphical data analysis
Index velocity rating regression output
Rating validation plots

Example Index Velocity Rating Spreadsheets

Index-velocity streamgage with unidirectional flow
Index-velocity streamgage with bidirectional flow

Example Station Descriptions and Station Analyses

Examples of station descriptions and analyses that conform to the minimum requirements specified in OSW Technical Memo 2015.05 are given below.

Station Description - ID WSC (pdf) | (SIMS) USGS only
Station analysis - ID WSC
Detailed station analysis - FL WSC