A numerical model for simulating Hortonian overland flow on tropical hillslopes with vegetation elements

This paper describes a two-dimensional hydrodynamic model that characterizes surface runoff process resulting from a varying rainfall intensity event, on an infiltrating soil surface. The soil surface has spatially varied soil physical, hydraulic and microtopographic characteristics. Infiltration process is modelled with the Philip two-term equation and the time before ponding approximated with the time compression algorithm. Vegetation is modelled as a dynamic component with the modified Gash model. The equation is solved with a modified second order Leapfrog explicit finite difference scheme with centred time and space derivatives. The model was validated with standard analytical solutions. Evaluation with results from field campaigns in the Volta Basin of West Africa during the 2002 rainfall season indicates good agreement, with r(2) values ranging from 0.89 to 0.96. The developed method will be useful in studying the dynamics of surface runoff generation under complex microtopographic conditions, spatially varying soil hydraulic characteristics and temporally dynamic rainfall intensity, as found in many tropical catchments. Copyright (c) 2007 John Wiley & Sons, Ltd.