A new integrated surface and subsurface flows model and its verification

Abstract

A new coupled model for simulating surface and subsurface flows in a fully integrated way is presented. This model contains two sub-models; one is the 2D kinematic wave approximation of the Saint Venant’s equations used to model runoff, and another is Richards’ equation for variably saturated subsurface flow. In this model, boundary conditions (the conditions describing groundwater discharge at the land surface or surface water infiltration into the subsurface) could be eliminated through mathematic transformations of the governing equation of surface and subsurface flows. The solution of surface and subsurface flows could be simultaneous. And the surface domain and subsurface domain could be considered as a fully integrated domain. This approach naturally provides pressure and fluxes continuity along land surface. In order to assess this modelling approach, several classical validations, verification and application test cases are presented. For overland flow solely, the model is compared to an analytical solution and to commonly use hydrological models. The integrated model is then validated with a sandbox laboratory experiment and a soil column test. Finally, the effects of rainfall intensity, hydraulic conductivity of soils and initial bulk water content of soils to runoff and infiltration of a homogeneous soil slope are studied under different conditions.