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In cooperation with the Texas Department of Transportation

Techniques to Estimate Generalized Skew Coefficients of Annual Peak Streamflow for Natural Basins in Texas

By Linda J. Judd, William H. Asquith, and Raymond M. Slade, Jr.

U.S. Geological Survey
Water-Resources Investigations Report 96–4117


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pdf (539 KB)


Contents

Abstract

Introduction

Purpose and Scope

Previous Investigations

Station Skew Coefficients

Techniques to Estimate Generalized Skew Coefficients

Regression Equations

Generalized Skew Coefficient Map

Summary

Selected References

Figures

1–4.  
Maps showing:
 
1.  
Generalized skew coefficients developed for Texas by the U.S. Water Resources Council
 
2.  
Hydrologic regions for Texas
 
3.  
Generalized skew coefficients developed for Texas during this investigation
 
4.  
Locations and site numbers of streamflow-gaging stations used in developing generalized skew coefficient map for this investigation

Tables

1.  
Selected data and basin characteristics for streamflow-gaging stations having at least 20 years of data from natural basins in Texas
2.  
Generalized skew coefficients developed by the U.S. Water Resources Council, station skew coefficients, and generalized skew coefficients (this investigation) for streamflow-gaging stations having at least 20 years of annual peak-streamflow record from natural basins in Texas
3.  
Characteristics of regression equations to estimate generalized skew coefficients

Abstract

This report presents two techniques to estimate generalized skew coefficients used for log-Pearson Type III peak-streamflow frequency analysis of natural basins in Texas. A natural basin has less than 10 percent impervious cover, and less than 10 percent of its drainage area is controlled by reservoirs. The estimation of generalized skew coefficients is based on annual peak and historical peak streamflow for all U.S. Geological Survey streamflow-gaging stations having at least 20 years of annual peak-streamflow record from natural basins in Texas. Station skew coefficients calculated for each of 255 Texas stations were used to estimate generalized skew coefficients for Texas.

One technique to estimate generalized skew coefficients involved the use of regression equations developed for each of eight regions in Texas, and the other involved development of a statewide map of generalized skew coefficients. The weighted mean of the weighted mean standard errors of the regression equations for the eight regions is 0.36 log10 skew units, and the weighted mean standard error of the map is 0.35 log10 skew units. The technique based on the map is preferred for estimating generalized skew coefficients because of its smooth transition from one region of the State to another.




U.S. Department of the Interior, U.S. Geological Survey
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Last modified: Friday, September 16 2005, 04:23:52 PM
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