In this study we estimate the risk of water erosion in coastal watersheds between M'diq and Fnideq located in northern Morocco, through using a new approach based on spatial cartography. Precisely, the methodology adopted here integrates a Geographic Information System (GIS) with the universal soil loss equation (USLE). The field data includes three major components namely, lithology, degree of slope and vegetation density. Each of these components is represented by a separate layer, in which 1 to 5 value expresses its lateral variability degree. The final map of water-erosion risk is obtained by the sum of superposed indices, separately assigned to three thematic layers (facies, slope and vegetation cover), and multiplied by the percentages of the contribution of each factor to determine the percentage of weighting. . Secondarily, a complementary table translates the cartographic values of each layer as percentage values expressing the impact exerted by the corresponding risk factor throughout the studied area. The risk map is deducted after validation of these weightings on the field by choosing checkpoints distributed throughout the watersheds of the site. This method would allow for the tracking and of course monitoring of water erosion on a larger scale and to better direct the administrations concerned to the priority of installations.