Estimation of Soil Erosion and Sediment Yield using the GEOWEPP Model in Wadi El Malleh Watershed, Morocco

Abstract

Soil erosion is the most important soil degradation process in Morocco and a major environmental and economic concern that threatens the sustainability of dam reservoirs and agricultural lands. Moroccan soils face high erosion rates which exceed tolerable thresholds. In order to develop a comprehensive plan for soil and water conservation, it is crucial to describe the rate of soil erosion and sediment transport in the watershed over spatial and time scales. In this study, The GeoWEPP model was used for the first time in Wadi El Malleh watershed to glean useful information to guide soil conservation planning and management. The most susceptible soil units to erosion were identified along with the land use/management types associated with extremely high erosion rates. The analysis of onsite and offsite erosion assessment results across the different watershed allowed us to identify the most critical sub watersheds. The hillslopes dominated with the couple winter wheat, conventional till management/soil unit 15 (Vertisol) on the steepest slopes were associated to the highest erosion rates between 88.9 t/ha/yr and 135 t/ha/yr in the four sub watersheds identified as most critical and prioritized for soil conservation strategy assessment. A 90% reduction of soil loss rates was achieved by changing the hillslope land uses/management from winter wheat, conventional till to alfalfa with cuttings. Important insights that were gleaned from the use of GeoWEPP model in this study have the potential to increase the effectiveness of soil conservation planning in Wadi El Malleh watershed.