Ground-water discharge from the Coastal Plain of Virginia

The Chesapeake Bay and other important surface- water bodies receive ground water that discharges directly from the Coastal Plain of Virginia. This report presents estimates of the average annual ground-water discharge from the Coastal Plain of Virginia using two approaches. Average annual ground-water discharge from 16 gaged watersheds in the Coastal Plain of Virginia estimated by use of a streamflow hydrograph-separation approach ranged from 7.5 to 12.5 inches per year; the median was 10.8 inches per year. These estimates are similar to those reported by other investigators for the Coastal Plain in the nearby Delmarva Peninsula. Average annual ground-water discharge also was estimated by use of a hydrogeologic-area approach. In this approach, areas that have similar hydrogeologic charac- teristics are grouped and multiple regression is used to determine the relation between the hydro- geologic areas and ground-water discharge. The multiple-regression analysis indicates that ground-water discharge within the Coastal Plain of Virginia is a function of the relative areal extent of well-drained uplands and moderately well-drained uplands. On the basis of the hydro- geologic-area approach, ground-water discharge from the Coastal Plain of Virginia averages 9.9 inches per year.