Study on Interaction between Surface and Subsurface Flows using Conjunctive Flow Model

Abstract

The interaction between the surface and subsurface flow components plays an important role especially in initial loss and overland flow initiation at the early stage in rainfall events. Therefore, coupling of the surface and subsurface flow submodels is necessary in more comprehensive and sophisticated watershed modeling to deal with the interaction theoretically. We already proposed the conjunctive 2-D surface and 3-D subsurface flow model using an approximate version of the Saint-Venant equations to simulate the two-dimensional unsteady surface flow and a modified version of Richard’s equation for the three-dimensional unsaturated and saturated unsteady subsurface flow [1, 2]. This paper shows a further development of the conjunctive model and focuses on the interaction between surface and subsurface flow components. The interaction of the two components is directly related to the estimation of effective rainfall or initial loss of hyetographs. In the conjunctive model the interaction is formulated using the comparison of the two parameters,“rainwater supply”and“infiltrability (infiltration capacity)”. The model reproduces the initiation of overland flow and initial loss process and contributes to more precise and reliable estimation of effective rainfall than the usual methods using the empirical formulas in watershed modeling.