|Zheng, Fenli - INST. SOIL & WATER CONSV.|
|Huang, Chi Hua|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 17, 1999
Publication Date: January 1, 2000
Citation: Zheng, F., Huang, C., Norton, L.D. 2000. Vertical hydraulic gradient and run-on water and sediment effects on erosion processes and sediment regimes. Soil Science Society of America Journal. 64:4-11. Interpretive Summary: During rainfall, soil detachment, transport and deposition processes occur simultaneously. As runoff with variable sediment concentration moves downslope, it is possible that the change in sediment concentration can affect erosion processes, i.e., detachment, deposition and transport, on a downslope segment. However, there is little experimental data to show how run-on water and sediment concentration affects erosion processes downslope. A laboratory rainfall simulation experiment, using a specially designed soil box system, was conducted to examine the upslope runon effects on erosion processes at a hillslope segment. This soil box system has two soil boxes simulating an upslope sediment source area and a downslope test segment. Results showed that under free soil drainage conditions, a decrease in upslope run-on sediment content caused a corresponding increase in downslope sediment detachment. Under artesian seepage conditions, sediment deliveries were 3 to 6 times greater than those under drainage condition and the sediment regime was mainly controlled by the transport process. These results demonstrated the capability of using a dual-box system to quantify erosion processes on the hillslope and the importance of including surface hydrologic effects in developing process-based erosion prediction models. IMPACT: This research leads to new concepts and procedures in quantifying hillslope erosion processes. The findings will benefit erosion researchers and soil conservationists in developing erosion prediction models and erosion control practices.
Technical Abstract: Water and sediment from upslope areas affect erosion processes on a downslope segment. The detachment potential of the runoff water will decrease as the sediment content is increased until a sediment transport capacity, Tc, is reached and the excessive amount of sediment beyond Tc will then be deposited. This concept has not been tested experimentally. A dual-box system, a 1.8-m long sediment feeder box and a 5-m long test box, was used to quantify run-on water and sediment effects. The test box has holes at the bottom for controlling the vertical hydraulic gradient. Experimental variables were rainfall intensity, slope steepness, near- surface hydraulic gradient and run-on sediment concentration. Results demonstrat that under free soil drainage conditions, a decrease in run-on sediment content caused a corresponding increase in downslope sediment detachment resulting in a relatively constant sediment delivery from the test box. Under artesian seepage conditions, sediment deliveries were 3 to 6 times greater than those under drainage conditions and decreased as the erosion event progressed, possible due to a reduction in soil erodibility. Sediment detachment by the run-on water increased as the erosion event progressed. Sediment detachment by the run-on water increased as either slope or rainfall intensity was increased or when the surface was changed from a drainage to a seepage condition. These results demonstrated that the sediment delivery reached a dynamic equilibrium and the dual-box system can be used to study erosion processes similar to those occurring on a hillslope. A process-based erosion model needs to account for surface hydraulic conditions and the associated erosion processes and their interactions.