Contribution à l’évaluation de l’impact de l’aménagement des bassins versants de l’Oued Mellah et Allal El Fassi au Maroc
Résumé
Contribution to the assessment of the impact of watershed management of Oued Mellah and Allal El Fassi in Morocco. A holistic assessment approach is conducted in Oued Mellah and Allal El Fassi watersheds. The approach combines 3 quantitative methods (water and material flows at hydrometric stations, estimation of erosion rates using radioisotopes, monitoring linear erosion by gully picketing) and 3 qualitative methods (multidate mapping of erosion status, WOCAT method and assessment of avifaunistic biodiversity) that are complementary The monitoring has shown the interest of applying MUSLE model, which integrates all forms of erosion observed at watershed scale instead of RUSLE which evaluates only sheet and rill erosion, the efficiency of gabion check dams to reduce erosion by 50% and the importance of gully erosion as a source of sediment. Dry-stone cords and fruit plantations with conservation structures reduce erosion by 40% and fencing reduces it by 30%. Diachronic analysis of erosion status revealed a mixed efficiency of biological interventions. WOCAT method cataloged 4 good practices, and an assessment of avifaunistic biodiversity has shown a good nesting potential and an appreciable specific richness.