Impact of hydro-morphometric characteristics on the hydrological response of the Adoudou river watershed (Western Anti-Atlas, Morocco)

Resumen

The hydro-morphometric analysis of the Adoudou River watershed, located in the western Anti-Atlas of Morocco, aims to understand its hydrological response, particularly in the face of extreme floods that characterize this arid region. The absence of sufficient hydrometric data, typical of ungauged basins, justifies an approach based on the basin’s geometry, topography, and hydrography. The study relies on a Geographic Information System (GIS) using an SRTM Digital Elevation Model (DEM) and 1:50,000 scale topographic maps. To address inherent errors in the raw DEM, a hydrological correction was made based on the digitization of the hydrographic network and ridgeline extracted from the topographic maps. The quantitative analysis focused on the calculation and interpretation of a set of key parameters. Geometric parameters, such as the compactness index, circularity ratio, and equivalent rectangle, reveal an elongated basin shape, with a length eight times its width. Topographically, the hypsometric curve characterizes a mature basin, with steep slopes upstream contrasting with gentler slopes downstream. This steep upstream gradient is confirmed by the global slope index and specific relief. The hydrographic analysis, based on Strahler’s classification, identifies a seventh-order network. The confluence and length ratios, coupled with drainage and hydrographic densities, highlight the strong hierarchy and density of the network, particularly marked upstream. This spatial disparity in drainage density is corroborated by GIS mapping, reflecting the combined influence of topography and geology. Finally, the longitudinal profiles of the streams confirm this trend, with steeper slopes upstream influenced by the geological structure of the terrain. In summary, the hydrological response, particularly the torrential nature of Adoudou River floods, is strongly conditioned by the combination of topographic factors (steep upstream slopes), hydrographic factors (dense, hierarchical network), and geological factors (nature of the substrate). This study provides an essential basis for understanding hydrological risk management in this watershed.