Longitudinal Hillslope Shape Effects on Runoff and Sediment Loss: Laboratory Flume Experiments

Abstract

Catchment geomorphology is one of the most important factors governing runoff and erosion. However, its complexity is difficult to describe accurately; thus, for simplicity, many studies assume hillslopes with a uniform sloping profile. The influence of this simplification on estimating the rainfall-runoff and sediment loss processes is not well understood. In an effort to improve our understanding, this study relies on laboratory experiments using a movable rainfall simulator and a 6-m-long, 3-segment soil flume to simulate the effect of static and moving storms on differently shaped hillslopes: uniform, convex, concave, convex-concave, and concave-convex profiles. Therefore, variables, such as rainfall intensity, soil and water characteristics, and storm speed, were kept constant throughout the experiments. The work confirms empirically that storm movement and hillslope shape are central factors in the soil loss and overland flow processes. The results led to the following conclusions: (1) hillslope shape affected erosion for both nonmoving and moving rainstorms; (2) downslope moving storms led to higher runoff and sediment loss peaks than upslope moving storms; and (3) convex surfaces were the most hazardous in terms of the generation of runoff and erosion.