The simulation of the unsteady free-surface flow on infiltrating surfaces h
as many hydrological applications, including the study of overland flow, so
il erosion and conservation, surface irrigation and contaminant transportat
ion. The surface runoff is strictly connected to the infiltration through t
he soil surface; so, an independent simulation of the two processes, althou
gh very often adopted, may be unrealistic. This paper presents a mathematic
al model for simulating these interdependent surface and subsurface process
es. The model is based on the two-dimensional shallow water equations, coup
led with the one-dimensional Richards equation. These equations are integra
ted jointly, following the MacCormack scheme, which is an explicit, finite-
difference scheme, accurate to the second order. The model can simulate ini
tially dry surface conditions and variable initial soil water content, and
can deal with space-variable characteristics (slope, roughness and soil hyd
raulic properties). The accuracy of the model is tested by comparing its re
sults with analytical solutions and with experimental data. Finally, a nume
rical experiment carried out on a simple hypothetical catchment, both using
the complete model and a simplified version, in which the Richards equatio
n and the shallow water equations are solved in cascade, is discussed. (C)
2000 Silsoe Research Institute.