This research presents numerical simulations of small-scale rainfall simulator experiments using a process-based physical model. The model utilizes fundamental physical equations and analyzes the phenomena of surface runoff and water erosion. The adopted physical model is primarily composed of the shallow-water wave equation, Green-Ampt infiltration formula, and Hairsine-Rose equation. In the model, processes including water infiltration, splash erosion caused by rainfall, sediment entrainment carried by surface runoff, and sediment deposition are considered, aiming to simulate surface runoff, cumulative sediment yield, and eroded-terrain changes caused by water erosion. To assess the effectiveness of the numerical simulation results, the Nash-Sutcliffe efficiency coefficient (NSE) is used as the evaluation criterion. The laboratory rainfall simulator experiments using the same rainfall intensity (加入強雨強度) of three different slopes (10°、20° and 30°) were used as the studied cases Results of the simulations show that NSE values for runoff simulation reached 0.927 during the parameter calibration phase and exceeded 0.883 and 0.913 in the validation phases, respectively. The NSE for cumulative sediment yield simulation achieved 0.849 during parameter calibration and reached 0.997 and 0.983 in the validation phases. For cross-sectional microtopography simulation, the NSE attained 0.378 in the parameter calibration phase and achieveds 0.359 and 0.737 in the validation phases. In the case of longitudinal microtopography simulation, the NSE reached 0.937 during parameter calibration and attained 0.838 and 0.439 in the validation phase. This study presents the feasibility of the processed-based model in simulating surface runoff, sediment yield and eroded-terrain by water erosion.

(Key Words: Surface runoff, Soil erosion, Shallow-water equation, Green-Ampt infiltration formula, Hairsine-Rose equation)