Characterizing Overland Flow on a Preferential Infiltration Dominated Hillslope: Case Study

Abstract

Understanding overland flow behavior on a natural hillslope and its accurate modeling is essential in hilly watersheds to address many water resource related issues, such as flash flood, soil erosion, and agroforestry. This problem is complicated because the hydrologic influences of microtopography, vegetation characteristics, slope, and preferential infiltration on overland flow are highly interdependent and nonlinear. This study aims at characterizing the overland flow behavior on a natural hillslope by carrying out about 35 in situ experiments with various rainfall intensities and degrees of vegetation. Further, in order to compute an average Manning’s roughness coefficient, one dimension shallow water equations were solved using a finite volume method. The relationship of rainfall intensity and preferential infiltration rate, obtained from in situ experiments, was coupled with the overland flow governing equations. Apart from replicating field observations accurately, the model results established relationships among rainfall intensity, preferential infiltration rate, Manning’s roughness coefficient and time of concentration, and also quantified the influence of degree of vegetation and preferential infiltration rate on overland flow for the study plot.