LAUSR

Estimation of watersheds base flow as a component of subsurface runoff is of significant importance, in particular, in watersheds of high permeability where the contribution of base flow to total runoff is large compared to that of surface flow. Complex hillslopes in nature have a different profile curvatures (concave, straight, and convex) and plan shapes (convergent, parallel, and divergent). In this study, an excess saturation model is developed to estimate the soil moisture deficit (SMD) profile along complex hillslopes. A new equation is presented which can predict base flow of hillslopes according to the spatially averaged SMD and topographic index over the hillslope surface. It is concluded that the hillslope geometry can obviously affect hillslope saturation and SMD. Moreover, the effect of convergence on SMD is higher than that of divergence. The largest and smallest effects on SMD are related to the convex convergent hillslope and the straight divergent one, respectively. Finally, the results of the developed model are compared to those derived from the solution of the hillslope-storage Boussinesq (HSB) equations for complex hillslopes.