In this work, we present the results of study of physicochemical parameters of sediments from the retaining Sidi Chahed dam, and the use of GIS to achieve a relationship between the geological nature of the watershed and sediments of this retaining of dam from ASTER image. The physicochemical characterization of the sediments was make in order to determine the main factors that govern the exchanges of various forms of phosphorus at the water-sediment interface, and of determining the geological nature of the land crossed by the tributary waters feeding the dam retaining. The results obtained showed that the average values of carbonates of calcium and pH, which are respectively 36% and 8.3, are more important. The comparison of the geological map and the hydrographic network map shows that the majority of grounds crossed by the tributary waters feeding retaining of dam are the marl and limestone of Miocene, which increases the percentage of calcium carbonate in the sediments of the retaining of dam and therefore favors the dominance of fraction of phosphorus CaCO3 -P (76%) in sediments.

The Dam Sidi Chahed is located downstream of the Mikkes and Lmaleh rivers. It's located about 30 km at the NE of Meknes city and about 30 km at the NW of Fez city on the main road between Fez and Sidi Kacem. It was commissioned in 1997 and has a capacity of 170 million m3. It crosses three different structural units with the Middle Atlas to the south, the basin know the center and south-north Rif wrinkles. The use of ArcGIS and Global Mapper has been used to characterize the edge of the dam and its retention Sidi Chahed from ASTER images making several thematic maps which are: the map contours, the DTM, the map slopes and their exposure, thematic map of sub-basins, the thematic map of the river system and its classification, the superposition of the structural and drainage networks, thematic map of rainfall and late distribution maps of physico-chemical parameters. From thematic maps produced for the watershed studied, several geometric calculations were performed to characterize the watersheds under long view, width, equivalent rectangle, area, perimeter and compactness index. These parameters indicate that sub tanks are elongated favoring low flow rates, a greater flow of water and a total amount of time of considerable precipitation harvested. Rainfall results, which were obtained from the isohyets maps are divided into 7 classes with lower values since the Middle Atlas at the south (850 mm) to the Sidi Chahed dam at the north (450 mm).