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Scientific Investigations Report 2011–5143

Prepared in cooperation with the Virginia Department of Environmental Quality

Low-Flow Characteristics of Virginia Streams

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

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Low-flow annual non-exceedance probabilities (ANEP), called probability-percent chance (P-percent chance) flow estimates, regional regression equations, and transfer methods are provided describing the low-flow characteristics of Virginia streams. Statistical methods are used to evaluate streamflow data. Analysis of Virginia streamflow data collected from 1895 through 2007 is summarized. Methods are provided for estimating low-flow characteristics of gaged and ungaged streams. The 1-, 4-, 7-, and 30-day average streamgaging station low-flow characteristics for 290 long-term, continuous-record, streamgaging stations are determined, adjusted for instances of zero flow using a conditional probability adjustment method, and presented for non-exceedance probabilities of 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.02, 0.01, and 0.005. Stream basin characteristics computed using spatial data and a geographic information system are used as explanatory variables in regional regression equations to estimate annual non-exceedance probabilities at gaged and ungaged sites and are summarized for 290 long-term, continuous-record streamgaging stations, 136 short-term, continuous-record streamgaging stations, and 613 partial-record streamgaging stations. Regional regression equations for six physiographic regions use basin characteristics to estimate 1-, 4-, 7-, and 30-day average low-flow annual non-exceedance probabilities at gaged and ungaged sites. Weighted low-flow values that combine computed streamgaging station low-flow characteristics and annual non-exceedance probabilities from regional regression equations provide improved low-flow estimates. Regression equations developed using the Maintenance of Variance with Extension (MOVE.1) method describe the line of organic correlation (LOC) with an appropriate index site for low-flow characteristics at 136 short-term, continuous-record streamgaging stations and 613 partial-record streamgaging stations. Monthly streamflow statistics computed on the individual daily mean streamflows of selected continuous-record streamgaging stations and curves describing flow-duration are presented. Text, figures, and lists are provided summarizing low-flow estimates, selected low-flow sites, delineated physiographic regions, basin characteristics, regression equations, error estimates, definitions, and data sources. This study supersedes previous studies of low flows in Virginia.

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, Low-flow characteristics of Virginia streams: U.S. Geological Survey Scientific Investigations Report 2011–5143, 122 p. + 9 tables 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

Monthly Streamflow Statistics

Flow-Duration Curves

Low-Flow Frequency Analysis

Conditional-Probability Adjustment

MOVE.1 Regression Equations for Short-Term, Continuous-Record and Partial-Record Streamgaging Stations

MOVE.1 Analyses for Short-Term, Continuous-Record Streamgaging Stations

MOVE.1 Analyses for Partial-Record Streamgaging Stations

Basin Characteristics


Definition of Regions

Model Development

Model Verification and Diagnostics

Weighting Multiple Estimates

Weighting of Independent Estimates

Low-Flow Characteristics

Other Methods for Estimation at Ungaged Sites

Example Applications

Use of Regression Equations

Drainage-Area Ratio Method

Ungaged Site with Nearby Gage

Gaged Site





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