In cooperation with the Texas Department of Transportation

Regional Equations for Estimation of Peak-Streamflow Frequency for Natural Basins in Texas

By William H. Asquith and Raymond M. Slade, Jr.

U.S. Geological Survey
Water-Resources Investigations Report 96–4307

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Purpose and Scope


Estimation of Peak-Streamflow Frequency

Historical Peak Streamflows

Low-Outlier Thresholds

Skew Coefficients

Selected Basin Characteristics

Regional Equations for Estimation of Peak-Streamflow Frequency

Regression Analysis

Regression Equations

Discussion of Regression Equations and Application


Selected References


Map showing locations of selected stations with natural basins in and near Texas


Map showing hydrologic regions of Texas
Graphs showing:
Example of peak-streamflow frequency analysis for station 08171000, Blanco River at Wimberley, Texas
Relation between 100-year peak discharge and contributing drainage area for streamflow-gaging stations in regions 5 and 7 of Texas
Graphs showing relation between basin characteristics for:
Region 1
Region 2
Region 3
Region 4
Region 5
Region 6
Region 7
Region 8
Region 9
Region 10
Region 11
Graphs showing comparison of weighted least-squares regression analyses for region 5


Peak-streamflow frequency estimates, analysis information, and basin characteristics for stations with at least 8 years of annual peak-streamflow data from natural basins within and near Texas
Regression equations for estimation of peak-streamflow frequency for hydrologic regions of Texas
Critical values of the t-distribution for selected confidence limits for regression equations
Covariance matrix for regression equations


ft3/s, cubic foot per second

ft/mi, foot per mile

in., inch

mi, mile

mi2, square mile


Peak-streamflow frequency estimates are needed for flood-plain management; for objective assessment of flood risk; and for cost-effective design of dams, levees, other flood-control structures, roads, bridges, and culverts. Peak-streamflow frequency represents the peak discharges for recurrence intervals of 2, 5, 10, 25, 50, and 100 years. The U.S. Geological Survey, in cooperation with the Texas Department of Transportation, conducted an investigation to develop regional regression equations for the estimation of peak-streamflow frequency for ungaged sites in natural basins in Texas. Peak-streamflow frequency data from streamflow-gaging stations in natural drainage basins of Texas were used.

Peak-streamflow frequency for 559 Texas stations with natural (unregulated and rural or nonurbanized) basins was estimated with annual peak-streamflow data through 1993. The peak-streamflow frequency and drainage-basin characteristics for the Texas stations were used to develop 16 sets of equations to estimate peak-streamflow frequency for ungaged natural stream sites in each of 11 regions in Texas. The relation between peak-streamflow frequency and contributing drainage area for 5 of the 11 regions is curvilinear, requiring that one set of equations be developed for drainage areas less than 32 square miles and another set be developed for drainage areas greater than 32 square miles. These equations, developed through multiple-regression analysis using weighted least squares, are based on the relation between peak-streamflow frequency and basin characteristics for streamflow-gaging stations. The regions represent areas with similar flood characteristics. The use and limitations of the regression equations also are discussed. Additionally, procedures are presented to compute the 50-, 67-, and 90-percent confidence limits for any estimation from the equations. Also, supplemental peak-streamflow frequency and basin characteristics for 105 selected stations bordering Texas are included in the report. This supplemental information will aid in interpretation of flood characteristics for sites near the state borders of Texas.

U.S. Department of the Interior, U.S. Geological Survey
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Last modified: Wednesday, December 07 2016, 01:27:29 PM
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