DEVELOPING A VERTICAL QUASI-TWO-DIMENSIONAL SUBSURFACE FLOW MODEL

Abstract

 Rainfall-runoff simulations were conducted by using an existing detailed hillslope flow model and a kinematic wave model. Investigations on the simulated hydraulic quantities revealed that soil moisture profile over a cross-section greatly influenced water flows in the slope downward direction and that the hydraulic gradient in the slope downward direction was deemed to be approximately the same as the slope gradient. Based on the above results, we developed a vertical quasi-two-dimensional subsurface flow model by approximating the hydraulic gradient in the slope downward direction with the slope gradient in the vertical two-dimensional Richards’ equation. The developed model was tested on a single slope against existing models. The runoff discharge and soil moisture simulated by the developed model matched well with those of the detailed model, which implies importance of considering soil moisture profile in rainfall-runoff modelings. The developed quasi-two-dimensional model reduced computation time to less than half that of the detailed model for most cases assumed in this study.