Perched Water Table Fluctuation Compared to Streamflow

Abstract

Perched water table-streamflow relationships above a fragipan were studied on a forested watershed in the Valley and Ridge Province of central Pennsylvania. Automatic recording wells, a weir, and an automatic rain gage were installed to monitor perched water table changes, streamflow, and precipitation continuously. Time of year and precipitation were the most significant factors affecting perched water table and streamflow levels. In winter and early spring, streamflow and the perched water table were high and sensitive to rainfall and temperature changes. Rapid freezing and thawing affected water levels within the recording wells and the stream. During late spring and summer, water loss due to evapotranspiration was the dominant factor in streamflow-perched water table responses. Diurnal fluctuations due to daily temperature variations were concurrently observed in both the stream and the perched water table. As the soil continued to dry in summer, streamflow ceased and water table response to rainfall declined. With heavy fall rains and low evapotranspiration, the perched water table reappeared and streamflow resumed. Increased streamflow and flooding due to large storms were greatest when the soil adjacent to the stream was saturated.