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Scientific Investigations Report 2011–5198

Prepared with support from the U.S. Geological Survey Groundwater Resources Program
in cooperation with the Virginia Department of Environmental Quality

Quantifying Components of the Hydrologic Cycle in Virginia using Chemical Hydrograph Separation and Multiple Regression Analysis

By Ward E. Sanford, David L. Nelms, Jason P. Pope, and David L. Selnick

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This study by the U.S. Geological Survey, prepared in cooperation with the Virginia Department of Environmental Quality, quantifies the components of the hydrologic cycle across the Commonwealth of Virginia. Long-term, mean fluxes were calculated for precipitation, surface runoff, infiltration, total evapotranspiration (ET), riparian ET, recharge, base flow (or groundwater discharge) and net total outflow. Fluxes of these components were first estimated on a number of real-time-gaged watersheds across Virginia. Specific conductance was used to distinguish and separate surface runoff from base flow. Specific-conductance data were collected every 15 minutes at 75 real-time gages for approximately 18 months between March 2007 and August 2008. Precipitation was estimated for 1971–2000 using PRISM climate data. Precipitation and temperature from the PRISM data were used to develop a regression-based relation to estimate total ET. The proportion of watershed precipitation that becomes surface runoff was related to physiographic province and rock type in a runoff regression equation. Component flux estimates from the watersheds were transferred to flux estimates for counties and independent cities using the ET and runoff regression equations. Only 48 of the 75 watersheds yielded sufficient data, and data from these 48 were used in the final runoff regression equation. The base-flow proportion for the 48 watersheds averaged 72 percent using specific conductance, a value that was substantially higher than the 61 percent average calculated using a graphical-separation technique (the USGS program PART). Final results for the study are presented as component flux estimates for all counties and independent cities in Virginia.

First posted May 30, 2012

For additional information contact:
Ward E. Sanford
USGS National Research Program
12201 Sunrise Valley Drive
Mail Stop 431
Reston, VA 20192-0002

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Suggested citation:

Sanford, W.E., Nelms, D.L., Pope, J.P., and Selnick, D.L., 2012, Quantifying components of the hydrologic cycle in Virginia using chemical hydrograph separation and multiple regression analysis: U.S. Geological Survey Scientific Investigations Report 2011–5198, 152 p.




Geologic Setting

Hydrologic Setting


Estimates of Hydrologic Budget Components

Estimates for Localities

Uncertainties in Estimates

Summary and Conclusions


References Cited

Appendix 1. Flow and specific conductance records

Appendix 2. Plots of mean monthly flow versus fraction base flow for the USGS gages

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