Contribution of Lateral Soil Water Movement above a Fragipan to Streamflow

Abstract

AbstractA water balance approach to the hydrologic budget on a small mountainous watershed in central Pennsylvania was used to determine if lateral water flow perched above a soil fragipan could be quantitatively related to streamflow. Perched water table fluctuations were measured using a grid of 60 observation wells and streamflow was recorded using a weir. This site was monitored in mid‐November when evapotranspiration was at a minimum and when no precipitation was recorded. Soil water yield due to perched water table decline was calculated, hydraulc conductivity and the rate of water movement through the soil computed, and the zone of water contribution to streamflow determined. Results indicated water yield from the soil aquifer explained streamflow. Saturated water flow was shown to be the main mechanism of water movement, although unsaturated flow may have been significant for short distances under low tensions. The major zone of soil water contribution to streamflow was the more poorly drained soils adjacent to the stream. Unsaturated soils on the upper mountain flanks had little affect upon streamflow because of their low gradient and their large distance from the stream.