Characterization of soil specific degradation for the northern region of Morocco
Water erosion is a major process of soil degradation. In Morocco, it is regarded as the principal cause of desertification. It involves a reduction of the production potential of soils and as the silting of dam reservoirs leading to a loss of the amount of mobilizable water and brings up the issue of resilience of these hydraulic infrastructures. Adverse effects are reflected in the domains of energy production and irrigation and drinking water supplies. To face this challenge, Morocco must multiply its interventions to assess the consequences of soil degradation and to develop suitable programs of soil conservation. In this context, a sample of 15 catchment area located in the northern part of Morocco was selected in order to analyze the silting over periods of 8 to 47 years. The bathymetric data was provided by the DRPE (Direction of the Research and the Planning of Water).This paper aims i) to characterize the Specific Degradation (DS) of the northern part of Morocco through the study of 15 catchment areas; ii) to deduce a range of variability from the DS in this area and iii) to assess the relevance of simple models based on basin area, or the combination of basin area and the annual average flow, to predict the DS. The adopted approach is based on the confrontation of a current measurement of the Specific Degradation (DS) derived from the bathymetric surveys with assessments of the latter using models established to predict the silting of dams in Morocco. The analysis of siltation in dam reservoirs by the investigation of bathymetric data over periods from 8 to 47 years, shows an annual average total silting of approximately 0.6*109 m3, that is13% of the initial total capacity which is about 4.6*109 m3 and a variability of the specific degradation ranging from 172 to 5 365 tkm-2yr-1, that is a ratio of1 to 31. To end with, this study shows a significant variability of the performances of prediction of specific degradation based on simple models using the area of watershed and water flow.
Key words: Water erosion, Dams, Silting, Specific degradation, Morocco