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Efects of hillslope geometry on soil moisture defcit and base fow using an excess saturation model

Afshar Ardekani Amin, Sabzevari Touraj

Acta Geophysica

2020

Vol. 68, no. 3

773--782

Estimation of watersheds base fow as a component of subsurface runof is of signifcant importance, in particular, in watersheds of high permeability where the contribution of base fow to total runof is large compared to that of surface fow. Complex hillslopes in nature have a diferent profle 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 defcit (SMD) profle along complex hillslopes. A new equation is presented which can predict base fow of hillslopes according to the spatially averaged SMD and topographic index over the hillslope surface. It is concluded that the hillslope geometry can obviously afect hillslope saturation and SMD. Moreover, the efect of convergence on SMD is higher than that of divergence. The largest and smallest efects 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.

Effect of hillslope topography on soil erosion and sediment yield using USLE model

Sabzevari T., Talebi A.

Acta Geophysica

2019

Vol. 67, no. 6

1587--1597

Catchment hillslopes in nature have a complex geometry. Complex hillslopes have different plans (convergent, parallel and divergent) and different curvature (straight, concave and convex). In this study, the erosion rates of the nine complex hillslopes were investigated using the universal soil loss (USLE) method. The topography factor (LS function) in the USLE was developed as a function of plan shape and profile curvature. The hillslopes studied were divided into sets of complex pixels and the erosion over the pixels was calculated. Total erosion was regarded as the sum of erosion of all pixels. Furthermore, to calculate the sediment delivery ratio of each pixel, a new travel time equation for complex hillslopes was employed. Results showed that the mean erosion of convex hillslopes was 1.43 times that of concave and 1.19 times that of straight slopes. The effect of curvature shape on erosion was much greater than plan shape effect. The highest erosion belonged to convex divergent slopes, and the least erosion was related to concave divergent slopes. The laboratory results intended for validation of the numerical model also show that in hillslopes with fixed plan, the erosion rate in the convex hillslopes exceeds that of concave and straight hillslopes. Also, in the hillslopes with fixed curvature profile, the erosion rate in the convergent hillslopes is more than in the divergent and parallel ones.