Water Erosion Risk Mapping and Materials Transfer in the Smir Dam Watershed (Northwestern Morocco)

Abstract

Over the last three decades, soil erosion phenomenon has grown to be the most serious and significant geo-environmental problem in Morocco as in the whole Mediterranean area. As a matter of fact, it damages both soil functions and quality, not to mention the magnification of the surface waters pollution along with the siltation of Dams and reservoirs. The Geographic Information System (GIS), in addition to other tools, has shown to be one of the key components used to model and assess potential erosion in a given area by estimating the rate of eroded soils and the amount of sediment carried out by either runoff or through rivers. The main aim of this paper consists, primly, in producing soil erosion risk map of the Smir Dam watershed (Northwestern Morocco) using the Universal Soil Loss Equation (USLE) adapted to Moroccan conditions and integrated into a GIS platform. The aforesaid equation allows the calculation, spatialization and overlying the five factors controlling water erosion, namely rainfall erosivity, soil erodibility, slope length and steepness, land use and erosion control practices. As a result, a spatial referenced document has been generated, representing, mostly, high erosion rates with an average loss of 45.45 t/ha/year. Furthermore, the spatial analysis of erosion phenomenon, related with other thematic maps, showed that the vegetation cover is the main factor that controls and affects the erosion in the Smir watershed.