Inflow Rate Impact on Hillslope Erosion Processes and Flow Hydrodynamics

Inflow water from upslope is an extremely important factor that influences downslope erosion processes. Little information is available concerning how inflow water affects downslope erosion processes in the Chinese Mollisol region, where a large amount of runoff is generated from upslope. The purpose of this study was to determine the effects of inflow rate on erosion processes and flow hydrodynamic parameters. A soil pan (10 m long, 1.5 m wide, and 0.5 m deep) was subjected to rainfall simulation and inflow experiments under one rainfall intensity (50 mm h(-1)), two slope gradients (5 and 10 degrees), and five inflow rates (50, 100, 150, 200, and 300 L min(-1)). The result showed that when upslope inflow was included, soil loss increased 12 to 1950 times compared with no upslope inflow. When rill erosion dominated, rill erosion accounted for 52 to 90% of the total soil loss as the inflow rate increased from 50 to 300 L min(-1). An increase in the inflow rate from 50 to 300 L min(-1) caused the flow velocity to increase 0.6 to 7.8 and 1.7 to 12.9 times at 5 and 10 degrees slopes, respectively, while the Darcy-Weisbach coefficient decreased from 13.5 to 95.4%. For sheet-dominated erosion, significant linear regressions were fitted between shear stress, stream power, unit stream power, and inflow rate; but for rill-dominated erosion, power functions were established between these flow hydrodynamic parameters and the inflow rate.