Sub-Watershed prioritization for soil and water conservation in the Upper Sebou Watershed (Middle Atlas, northern Morocco) using morphometric compound parameter analysis and GIS

Abstract

Soil erosion and land degradation pose a persistent threat to semi-arid mountain catchments, where steep relief, erodible substrates, and concentrated seasonal runoff drive high sediment loss. This study prioritizes the 53 sub-watersheds of the Upper Sebou watershed (Middle Atlas, northern Morocco; 7368 km²) for soil and water conser - vation through quantitative morphometric analysis. Basic basin parameters were extracted from a digital elevation model (DEM) in ArcGIS, from which the linear, areal, and relief morphometric parameters were computed using established mathematical formulas. Each parameter was ranked across the sub-watersheds, and the ranks were averaged to obtain a compound parameter (Cp) expressing the relative erosion susceptibility and conservation priority of each unit. Compound parameter values ranged from 19.63 to 38 and were grouped into five priority classes; 12 sub-watersheds (≈23%) were classified as very high and 17 as high priority. The very-high units form a contiguous core along the upper Sebou channel in the center of the basin, together with a detached pocket on the eastern flank, where high drainage density and relief coincide with compact watershed shapes that favor rapid runoff concentration. The drainage network and relief are densest along the central drainage corridor, where the highest-priority sub-watersheds are concentrated; these units also coincide with the more erodible lithologies and the sectors of lowest vegetation cover, which corroborates the ranking with information not used in its calculation. Overall, the approach offers an effective, low-cost means of pinpointing land-degradation hotspots and prioritizing conservation interventions, readily transferable to other data-scarce semi-arid basins.