Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) delivered a digital terrain model of a better spatial resolution and accuracy than the traditional free global DEM datasets at near-global coverage and made a wide range of detailed hydrologic applications feasible. In this study, the ASTER data is compared with the digitalized topographic contour DEM in hydrological analysis over the Loukkos catchment in Larache province, Morocco. Extracted stream network and flow directions were compared with the ones derived from the digitalized topographic maps. The result shows, for the stream network, more similarity in average altitude and large differences in lowlands as well as high elevations. For flow directions, the results are almost identical.

Digital elevation models (DEMs), as its name suggests, is a digital representation of ground in terms of altitude. It provides information not only on landforms but also on their geolocation; this is why it is considered one of the most useful digital data sets for a wide range of users. Various field, remote, and laboratory techniques can generate DEMs. Some of the DEMs such as ASTER, SRTM, and GTOPO30 are freely available open source products; however, the accuracy of these data sets is often unknown and is uneven within each dataset due to radar characteristics, type of topography, and physical properties of the surface. In this study, we evaluate open source DEMs (ASTER and SRTM) and their derived attributes using a reference DEM produced by contours maps interpolation and ground control points. In fact, the quality of derived attributes of DEMs such as slopes and drainage network is closely linked to accuracy of DEMs. While Open source DEMs partially show low accuracy in high elevation terrain and forest areas, it can be concluded that the quality of the datasets is sufficient in large scale studies.

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.