Contribution of morphological study to the understanding of watersheds in arid environment: A case study (Morocco)

Watershed planning is often based on the analysis of morphometric parameters, especially in poorly gauged or ungauged basins. These physiographic parameters have, in fact, a main role in water runoff. In many arid countries such as Morocco, there is a significant need for morphometric studies of watersheds to initiate integrated water resources management. For this purpose, we have carried out the watersheds delineation and morphometric analyses, using the Digital Terrain Model (DTM) and the Geographic Information System (GIS). We have applied this approach based on remote sensing and GIS in four sub-basins of the right bank of the Tensift watershed (Bourrous, Al Wiza, El Hallouf and Jamala). The shape indexes of Gravelius and Horton reveal elongated shapes of the four watersheds. In addition, the maximum slope and the drainage density do not exceed 27.15° and 1 Km/Km² respectively. The sub-basins do not have a very dense hydrographic network and the Strahler's drainage order is not very high (up to 5). The relief is not very high and do not reach 1000 m. These physiographic conditions do not allow a rapid runoff. The concentration times are precisely quite high (7 to 12 hours for watersheds of 161 to 401 km²). The use of a sufficiently fine DTM resolution and an appropriate GIS software would allow this kind of study to be very useful for effective watershed management.