Reconstitution of historical data and diagnosis of the current state of erosion control in the Nekor catchment
In Morocco, the silting in dams represents a tricky problem for the country. The total annual value of silting is estimated to 75 million m3. One of the strategic reservoirs, which displays these severe problems, is the dam of Mohamed Ben Abdelkrim Al Khattabi (MBAK). Sustained by the catchment area of Nékor and impounded in 1981, it constitutes the only source of water for the city of Al Hoceima and the surrounding urban centers (Imzouren, BéniBouayach, etc.). In view of the advanced gullying, the waterdeficit of soils, the absence of vegetation cover and the brutality of flooding in the catchment area of Nékor, MBAK dam silts up at prejudicial pace for its lifespan. Thus, and since 1976, the government undertook several developments of multisector origin (department of hydraulics, forest service, agriculture, equipment) in order to ensure the conservation of the capital "water-soil" and to protect MBAK dam. The present study aims to reconstitute the historical data and to put upa diagnosis of soil conservation work completed by the services of the Government. In relation to mechanical treatments, the diagnosis is based on the comparison between the initial state and the current state of 19 sedimentation walls out of21 in total. As for the biological treatments, 12 plots seton four reforestation perimeters were prospected by determining the dominant height, the density and the health status of plantations (Pin d’Alep, Pin Maritime and Eucalyptus Torquata). The effectiveness of soil conservation techniques was assessed using several indicators based mainly on field observations such as the state of the constructions compared to the initial profile, the success rate of plantations or the current state of the trees. Although the Government invested considerably in the realization of these installations, the results awaited with regard to sediment retention and silting reduction were not satisfactory. Indeed, sedimentation walls do not play anymore their role, asmost of them were partially or completely washed out by the first floods. As for the forestations, and in spite of a success rate generally exceeding 50 %, a significant portion of the plantations is infected by various pathogenic agents, which causes their decline.
Key words: Nékor Watershed, Mohamed Ben Abdelkrim El Khattabi Dam, Water erosion, Silting, Infrastructures, Assessment, Rif, Morocco