Factors Influencing Surface Runoff and Hydrologic Connectivity on an Agricultural Hillslope in Central Pennsylvania

Improved understanding of surface hydrologic processes is central to the targeted application of agricultural management practices for water quality protection. Factors influencing surface runoff production and hydrologic connectivity were explored at three landscape positions on a single hillslope located within a 27.4 acre agricultural watershed in central Pennsylvania. A total of 119 events (rainfall, rain-on-snow, and snowmelt) were monitored for total runoff volume (mL), water-table depth (0 cm - 45 cm), and soil-moisture content from 2002 to 2004 using 1- by 2-m plots at seepage slope, transportational midslope, and colluvial footslope positions. The seepage slope and transportational midslope plots were located in well-drained residual soils, whereas the colluvial footslope plots were located nearest the stream channel in somewhat poorly drained soils with clay fragipans. Poorly-drained soils in the colluvial footslope position generated more frequent (> 2 times) and significantly higher volumes of runoff (> 19 times) than the well-drained soils in the transportational midslope or seepage slope positions. Runoff generation on the colluvial footslope was predominately associated with elevated water-table depths and occurred most frequently during the late fall and winter months. In contrast, runoff generation on the well-drained seepage and transportational midslopes occurred most frequently during the summer months and was predominately associated with lower water-table depths (i.e. infiltration-excess surface runoff). Hydrologic connection, defined herein as runoff occurring simultaneously on the upslope and downslope plots, was observed for 39% of the events and occurred most frequently during the spring and early summer periods. The overall runoff trends observed in this study illustrate the importance of considering seasonal and landscape variables in agricultural watershed management.