Streamflow, ground-water levels, and precipitation at selected sites in the Potomac River Basin. Streamflow and ground-water levels in the basin typically vary seasonally with rates of precipitation and evapotranspiration. D.C. Streamflow can vary considerably from year to year. Floods occurred mostly during the months of winter and early spring.
Hydrologic conditions affect the quality of streams and ground water in the Potomac River Basin.
Fertilizers, pesticides, and other chemicals that are applied to the land surface may infiltrate to ground water or run off to streams during rainfall depending on the season, soil properties, and the intensity and duration of precipitation. Total streamflow and estimated ground-water contribution to flow in the South Branch Potomac River near Springfield, W. Va., during part of 1993. Ground water contributes virtually all flow to the river during dry periods but some of the flow during wetter periods. Va. Nitrate concentrations are typically higher during periods of high flow than during drier periods.