

Publications— Scientific Investigations Report 
By Dennis W. Risser, Ronald E. Thompson, and Marla H. Stuckey
View the report in Portable Document Format (PDF) SIR 20085185 (3.75 MB)
A method was developed for making estimates of longterm, mean annual groundwater recharge from streamflow data at 80 streamflowgaging stations
in Pennsylvania. The method relates mean annual baseflow yield derived from the streamflow data (as a proxy for recharge) to the climatic, geologic,
hydrologic, and physiographic characteristics of the basins (basin characteristics) by use of a regression equation.
Baseflow yield is the base flow of a stream divided by the drainage area of the basin, expressed in inches of water basinwide. Mean annual baseflow
yield was computed for the period of available streamflow record at continuous streamflowgaging stations by use of the computer program PART, which
separates base flow from direct runoff on the streamflow hydrograph. Base flow provides a reasonable estimate of recharge for basins where streamflow is
mostly unaffected by upstream regulation, diversion, or mining.
Twentyeight basin characteristics were included in the exploratory regression analysis as possible predictors of baseflow yield. Basin characteristics
found to be statistically significant predictors of mean annual baseflow yield during 1971–2000 at the 95percent confidence level were (1) mean annual
precipitation, (2) average maximum daily temperature, (3) percentage of sand in the soil, (4) percentage of carbonate bedrock in the basin, and (5) stream
channel slope. The equation for predicting recharge was developed using ordinary leastsquares regression. The standard error of prediction for the
equation on logtransformed data was 9.7 percent, and the coefficient of determination was 0.80.
The equation can be used to predict longterm, mean annual recharge rates for ungaged basins, providing that the explanatory basin characteristics can be
determined and that the underlying assumption is accepted that baseflow yield derived from PART is a reasonable estimate of groundwater recharge rates.
For example, application of the equation for 370 hydrologic units in Pennsylvania predicted a range of groundwater recharge from about 6.0 to 22 inches
per year. A map of the predicted recharge illustrates the general magnitude and variability of recharge throughout Pennsylvania.
Abstract
Introduction
BaseFlow Yield and Recharge
Previous Investigations
Purpose and Scope
Regression Method for Estimating Recharge Rates
Determining BaseFlow Yield for Basins
Basin Characteristics
Regression Techniques
Sensitivity of Predictions
Limitations of Regression Equations
Example Calculation
Recharge Estimates for Basins in Pennsylvania
Summary
References Cited
Suggested citation:
Risser, D.W., Thompson, R.E., and Stuckey, M.H., 2008, Regression method for estimating longterm mean annual groundwater recharge rates from base
flow in Pennsylvania: U.S. Geological Survey Scientific Investigations Report 20085185, 23 p.
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View the report in Portable Document Format (PDF) SIR 20085185 (3.75 MB)
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