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Scientific Investigations Report 2011–5144

Prepared in cooperation with the Virginia Department of Transportation

Peak-Flow Characteristics of Virginia Streams

By Samuel H. Austin, Jennifer L. Krstolic, and Ute Wiegand

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Peak-flow annual exceedance probabilities, also called probability-percent chance flow estimates, and regional regression equations are provided describing the peak-flow characteristics of Virginia streams. Statistical methods are used to evaluate peak-flow data. Analysis of Virginia peak-flow data collected from 1895 through 2007 is summarized. Methods are provided for estimating unregulated peak flow of gaged and ungaged streams. Station peak-flow characteristics identified by fitting the logarithms of annual peak flows to a Log Pearson Type III frequency distribution yield annual exceedance probabilities of 0.5, 0.4292, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002 for 476 streamgaging stations. Stream basin characteristics computed using spatial data and a geographic information system are used as explanatory variables in regional regression model equations for six physiographic regions to estimate regional annual exceedance probabilities at gaged and ungaged sites. Weighted peak-flow values that combine annual exceedance probabilities computed from gaging station data and from regional regression equations provide improved peak-flow estimates. Text, figures, and lists are provided summarizing selected peak-flow sites, delineated physiographic regions, peak-flow estimates, basin characteristics, regional regression model equations, error estimates, definitions, data sources, and candidate regression model equations. This study supersedes previous studies of peak flows in Virginia.

Revised April 30, 2013

First posted April 3, 2012

For additional information contact:
Samuel H. Austin
U.S. Geological Survey
1730 East Parham Road
Richmond, VA 23228
Telephone: 804–261–2620
Fax: 804–261–2659

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Suggested citation:

Austin, S.H., Krstolic, J.L., and Wiegand, Ute, 2011, Peak-flow characteristics of Virginia streams: U.S. Geological Survey Scientific Investigations Report 2011–5144, 106 p. + 3 tables and 2 appendixes on CD. (Also available online at




Purpose and Scope


Physical Setting

Coastal Plain


Blue Ridge

Valley and Ridge

Appalachian Plateaus

Previous Studies


Site Selection

Data Evaluation

Flood-Frequency Analysis

Basin Characteristics


Definition of Regions

Model Development

Model Verification and Diagnostics

Weighting Multiple Estimates

Weighting of Independent Estimates

Peak-Flow Characteristics

Other Methods for Estimation at Ungaged Sites

Examples of Calculating Peake-Flow Estimates

Use of Regression Equations

Drainage-Area Ratio Method

Ungaged Site with Nearby Gage

Gaged Site





Appendix 1. Curves and residual plots for candidate single-parameter regional egression equations for estimating peak flows of streams in Virginia

Appendix 2. Curves and residual plots for candidate multi-parameter regional regression equations for estimating peak flows of streams in Virginia

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