Regional-Scale Modeling of Water Erosion and Sediment Yield in a Semi-Arid Context: Case Study of Ziz Upper Watershed in South-Eastern Morocco

Abstract

On-site, the main impacts of soil erosion worldwide are the decrease in the productivity of agricultural land and off-site, the significant problems are the siltation dam and increased risk of flooding. Many studies showed that several natural and anthropogenic factors have combined to aggravate soil erosion of Mediterranean agroecosystems, the climate, high sensitivity to soil erosion, the intensification of human activities, and cultural practices for centuries. The severity of this problem in Moroccan mountain agroecosystems has generated a demand for soil loss monitoring. Currently, much different erosion and sediment transport models are available. Spatially distributed erosion models are excellent tools to simulate and predict the spatial distribution of soil erosion and sedimentation under different conditions. In this study, WaTEM/SEDEM was applied in Ziz upper watershed (4435 km-2) in southeast Morocco. Model calibration and validation were performed based on 37 years of recorded sediment yield at the Hassan Addakhil's dam. This application estimates the total sediment supply from hillslopes to the river network at 2.02 106 t. yr-1 and specific sediment yield at 4.58 t ha-1yr-1. These results were lower than those recorded at the catchment outlet. Water erosion was the predominant process of soil redistribution, whereas tillage erosion was not significant. This simulation allows the primary sediment sources situate in the upper parts of the southwest-facing slope and some sinks within the catchment. The spatial distribution knowledge of erosion processes is a useful tool for proposing the best strategies for erosion control.