Seepage and soil erosion for a clay loam soil

Seepage on a hillslope produces an area susceptible to surface erosion, especially near the bottom of the slope. A laboratory study was conducted to quantify the effects of seepage on soil erosion for the Glynwood clay loam (fine, illitic, mesic Aquic Hapludalf). A 5-m-long, 1.2-m-wide soil box with adjustable slope gradient and water table control was used. A plate was installed in the soil box to force water seepage. Erosion from simulated rainfall and concentrated Bow was studied. For the rainfall experiment, the soil box was set to 10% slope and exposed to a sequence of three multiple-intensity storms, ranging from 25 to 100 mm h(-1), every 2 d. For the concentrated Bow experiment, five inflow rates ranging from 3.8 to 30.2 L min(-1) were applied to 0.2-m-wide Bow channels. Flow experiments were conducted at 5 and 10% slopes and for several different seepage and drainage conditions at the 5% slope. Sediment concentrations under seepage conditions averaged 22% higher than those under free drainage with simulated rainfalls. For concentrated flow conditions, sediment concentrations under seepage were approximately 81% higher at the 10% slope. At the 5% slope, sediment concentrations were six times higher for a surface under 20 cm seepage pressure compared with a surface drained for 7 d. Visually, it was observed that seepage greatly increased soil erosion because of its effects on headcut development. A process-based erosion prediction model, such as WEPP, should be expanded to predict seepage conditions and their effects on headcutting.