Résumé:
The watersheds of the wadis of Lagreme and Kissir know degradations and losses of soil over time. The geo-geomorphological and morphometric properties such as lithology, morphology, slope and vegetation of the two basins are an important factor that promotes water erosion and generally a significant specific solid transport. The action of precipitation is a function of their intensity on the soil, they come into play and cause an erosion often accelerated. The sediments resulting from this soil degradation contribute to the siltation of the reservoir dam. The lithological formations outcropping in the study area have an influence on the installation of a network of ravines and gullies and on the behavior of superficial flows. Slope erosion remains a complex and dissimilar phenomenon from one basin to another; it is irregular within the same basin due to local geo-geomorphological and morphometric conditions. This study aims to establish a hierarchy of watersheds of the two wadis Lagreme and Kissir, based on morphometric indicative indices. The present work also aims to draw up thematic maps using a geographic information system (GIS) of the different processes related to water erosion, such as slopes, lithology, precipitation, and vegetation. The integration in the GIS of the various digital maps, allowed to codify the degree of vulnerability of the various parameters having impact on the water erosion in the two watersheds that are the subject of the study. The spatialization of the risk of erosion was established based on the estimate of the severity of the six factors presenting the parameters of the soil erodibility: slope, lithology, precipitation, flow, land use and lineaments. The additive combination of the various maps integrated into the GIS enabled the mapping of different classes of soil sensitization to erosion: low, medium, strong and very strong. The mapping of the degree of erosion risk was established on the principle of superposition of the different thematic maps developed using a geographic information system. Areas marked by strong and strong erosion sensitivity (orange and red color) in both basins require immediate anti-erosion interventions.
