ARS | Publication request: Numerical Model for Coupled Overland Flow and Variably-Saturated Subsurface Flow

Submitted to: Soil Science Society Of America Annual Meeting
Publication Acceptance Date: August 1, 2004
Publication Date: October 1, 2004
Citation: Simunek, J., Matson, E.D., Van Genuchten, M.T., Ankeny, M.D. 2004. Numerical Model For Coupled Overland Flow And Variably-Saturated Subsurface Flow. (Cd-Rom). Soil Science Society Of America Annual Meeting. Oct. 31 - Nov. 4, 2004. Seattle, Wa.

Technical Abstract: Water flow and solute transport on a hillslope is a complex nonlinear problem. Rain water initially infiltrates at a rate equal to the rainfall rate. Once the soil infiltration capacity is reached, surface runoff is generated which then redistributes water along the land surface. To describe these complex interactions we coupled the HYDRUS-2D software package, simulating water flow and solute transport in variably saturated porous media, with a newly developed overland flow routine. The subsurface solver uses Galerkin finite elements for spatial discretization, and a fully implicit finite differences method for temporal discretization. The overland flow solver uses fully implicit four-point finite difference method to numerically solve the one-dimensional kinematic wave equation, with overland fluxes evaluated using Manning's hydraulic resistance law. A Picard iterative solution scheme is invoked to solve the resulting system of nonlinear equations. The subsurface flow module determines the main time step for the coupled system. If required for numerical stability, the overland flow module can use multiple smaller time steps during the main time step. This type of time management considers the fact that overland flow and variably-saturated subsurface flow often run at quite different time scales. We will present several examples of the updated HYDRUS-2D program showing the development of overland flow when the infiltration capacity is exceeded.