Dams Siltation and Soil Erosion in the Souss-Massa River Basin

Siltation of 26 large and small dams, spatially distributed in the Souss–Massa basin, has been investigated. The disparity observed in the reservoir’s silting reflects the variability of each watershed’s physical parameters that control the water erosion. These parameters include in particular lithology, topography, climate, vegetation, hydrology, and human actions. The hardness of the water erosion quantification due to the lack of data and variability of climate in the region pushes many researchers to suggest the deduction of the watershed’s specific degradation from the annual siltation stored in reservoirs. This approach enables us to characterize the erosion phenomenon exerted in the basin. In our study area, the most eroded areas are (1) the western High Atlas with alpine orogeny, tectonically unstable, marl lithology, and meandering rivers and (2) areas of high altitudes where igneous rock alteration offers an arena easily carted by bed load transport favored by steep slopes. In contrast, the least eroded areas are (1) the Anti-Atlas watersheds with Pan-African orogeny, tectonically stable with low steepness of terrain slopes, (2) areas of plains, and (3) watersheds with successful management practices as stone bands. This distribution is consistent with the results of previous studies by modern methods that are partial and localized. So, when the high erosion risk areas are assessed in a specific region, this kind of study allows us to indicate the areas which need the management practice in the aim to reduce erosion and maybe to select the suitable sites for large and small dams.