A Laboratory Experimental Investigation On Watershed Runoff And Sedimentation Processes

The Loess Plateau was morphologically formed with various small watersheds, which deliver enormous sediments into the Yellow River. The studies on the erosion mechanism and runoff and sedimentation processes is of great significance to the prediction of soil and water losses and to the implementations of soil and water conservational practices.A series of laboratory rain simulation experiments were conducted at the State Key Laboratory of Soil Erosion and Dry-land Farming on the Loess Plateau, Chinese Academy of Sciences, with a watershed model of 66 m2. To accurately present the watershed, a special device was developed to measure the topographic elevation of the watershed at a resolution of 0.1 by 0.1 m. The DEM of the watershed was generated with GIS software. Comparison of the representative points of the watershed with the measured data found the accuracy of the measurements to be ±0.005 m. The difference between the elevations before and after a rainfall event was used to estimate the soil erosion distribution in the watershed.The runoff and sedimentation processes were investigated under different rainfall intensities and durations, with rainfall intensities at 25, 50, 75 mm/hr and at durations of 5, 10, 20 and 40 min. Sediment sensors were used to measure the suspended sediment concentrations (process) at the outlets of the watershed and the branch channels. Weirs and water level sensors were used to measure the runoff processes at the same locations where sediment measurements were taken. The flow velocities in the channels were measured with the sensors for shallow water flow velocity. The results indicated that with increase in rainfall intensity, faster increase in runoff was induced and the peak runoff volume was proportional to the rainfall intensity, and longer rainfall duration was associated with prolonged stable runoff. Sediment concentration increased with rainfall intensity, with continuous increase trend with time under lower rainfall intensity. The runoff processes were well coupled with the runoff processes. The flow velocities at the stable stage in the channels increased with rainfall intensity, with no significant influences from the rainfall duration.The investigation presents the runoff, sedimentation, erosion development processes and erosion distribution, which supplies a controllable experimental system for the study on watershed erosion mechanism, which is of great importance to watershed erosion model and soil and water conservation practices.