Simulation of runoff and infiltration using iterative cross-coupled surface and subsurface flows

Abstract

An iterative cross-coupled surface and subsurface flows model is proposed to simulate the runoff generation and infiltration of a wide area hillside slope. Surface water on hillside slope was modeled as 2D shallow water equations and subsurface flow was modeled as 3D Richards's equation. The infiltration capacity was estimated by Green-Ampt infiltration model. The water depth calculated by 2D shallow water equations was applied to 3D Richards's equation as the water head boundary condition and the infiltration or exfiltration calculated by Richards's equation was applied to the runoff simulation as source item. In this study, first, an approximation of shallow water equations that simplifies the equations of motion by considering only the main contributions was used. Then, the simplified runoff model was validated by the extensively used tilted impermeable V-catchment example with only simulating surface runoff flows. The iterative cross-coupled surface and subsurface flows model was verified by a simple 2D unsaturated-saturated model. The simulation results show that the iterative cross-coupled surface and subsurface flows model can reproduce rainfall generated runoff and infiltration. Finally, the runoff generation and infiltration of a natural mountain slope in Hokkaido were simulated, as the runoff caused several slope failures in this area during Typhoon 10 in 2016.