Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/1995
Publication Date: N/A
Interpretive Summary: Seepage on the hillslope reduces the strength of the surface soil and, therefore, produces an area susceptible to water erosion. Effects of hillslope seepage have been associated with the development of seepage steps and the initiation of gullies on the landscape. Little work was focused on quantifying the seepage effects. A special laboratory soil bed was designed to create the seepage condition. Simulated rainfall and concentrated flow experiments were conducted for the Glynwood clay loam. Results from the lab experiment showed that seepage greatly increased erosion, especially under concentrated flow conditions. A small water tension or drainage gradient near the surface can increase soil strength and greatly reduce erosion. Water drainage from the seepage area appears to be an effective way of controlling erosion caused by seepage.
Technical Abstract: Seepage on the 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. 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 flow 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, every 2 days. For the concentrated flow experiment, five inflow rates ranging from 3.8 to 30.2 L min**1 were applied to 0.2-m wide flow 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 as compared to a surface drained for 7 days. 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.