Application of GIS to study the physiographic factors and the water resources in the watersheds of Essaouira, Morocco

International audienceWater resources in the area of Essaouira, like other regions of Morocco, have experienced a significant drop in quality and quantity. This situation has led to the reduction of agricultural productivity and the degradation of several ecosystems. Topographic, morphological, hydrographic and climatic characterization and surface geology have influences on the hydrological behavior of the watershed and precisely the flow regime (surface water) and infiltration (underground water). The application of Geographical Information Systems (GIS) made it possible to evaluate the physical factors of the watersheds constituting the western part of Essaouira Basin (Coastal Zone) where the watershed of Ait Tahria presents an elongated form with slight slopes and strong relief, while the slopes are relatively high with strong relief for Qsob and Tidzi watersheds. The results obtained will allow us to say that the physiographic parameters of the watersheds and the geological nature of the saturated zone and the unsaturated zone have an influence on the physical reservoir parameters of the region. This influence is remarkable at the NE portion of the Ait Tahria basin, known for its low slope, large drainage area and Cretaceous (marl and marl-limestone) geological formations where the value of the conductivity Underground water is very high. This salt and mineralized water exceeds the standards of potability