Cartographie de l'occupation des sols en relation avec les mouvements gravitaires et le ravinement dans le Rif nord-occidental (Maroc)

In the western part of Morocco, various studies deal with land use (LU) mapping and analysis. However, no quantitative or qualitative analysis has been focused on the interrelations between mass wasting (MW) and LU. This paper is centered on the mapping in the NW Morocco (Chefchaouen province) to define different LU classes and their consequences for slope stability. Seven classes of LU were mapped: dense forests, shrubs or matorrals, reforestation areas, farmlands, naked areas, urban zones and free water bodies. Four major types of MW occur within this region: landslides, rock falls, debris flows and undercutting. Badlands (BL) do not belong to MW but are characterized by successive thalweg and crests resulting from linear erosion, also responsible for the loss in farmlands. Therefore, their location and extension are analyzed. The analysis of the spatial distribution of MW according to LU classes demonstrated that high densities of MW and BL classes cover three main LU classes: farmlands include 45% of MW and BL; dense forest's areas reach up to 24% of the phenomena, commonly due to an important local clearance of vegetation; shrubs are concerned by 11% of the MW only, in conformity with the discrete character of their plant cover. Landslides, river undermining and badlands are mostly triggered by farmlands. Debris flows and rock falls develop where steep rocks and resistant formations (limestone, sandstone, and quartzite) dominate, in association with marquetry of shrubs and islands of dense forests.