DYNAMICS OF MOVING BOUNDARY OVERLAND FLOWS OVER INFILTRATING SURFACES AT HILLSLOPES

The three flow processes occurring on hillslopes (overland flows, streamflows, and subsurface saturated-unsaturated flows) are in dynamic equilibrium and interact continuously through their common boundaries. A physics-based, deterministic, distributed model incorporating internal coupling of the three components is developed to study the extent and location of saturated regions neighboring the streams. These saturated zones develop overland flow and are very responsive to rainfall and are therefore important contributors to the hillslope hydrograph. Using a wide channel which drains the water from the side hillslopes (resembling an open book) for a physical section, we study the response of these variable source areas (VSAs) to various hydrologic and topographic parameters. An infiltrating boundary condition, which allows for both the Horton and Dunne mechanisms of overland flow generation, is incorporated in the analysis. It is observed that the dynamic modeling of the VSAs is useful for determining the hillslope hydrograph properties.