Modeling and mapping the risk of water erosion through the application of GIS and PAP/CAR directives. Case of the Upper Oum-Erbia Watershed, Morocco.

Abstract: Modeling and mapping the potential risks of water erosion of soils is of great importance in the management and planning of watersheds. This study aims to develop the map of soil vulnerability to erosion in the upper Oum-Rbia watershed in the central Middle Atlas, based on the guidelines of the Priority Action Programs / Center for Regional Activity (PAP / CAR). This method consists to defining the main causant factors (lithology, slope, erodibility, land use, density of plant cover, forms and extent of erosion existing on the ground) and uses a set of data (Geology, DTM, field trip...) using GIS and remote sensing. The watershed of the upper Oum-Erbia spreads over an area of 515.19 Km2, covers two geomorphological units including the tabular Middle Atlas and the folded Middle Atlas. The application of the PAP/CAR method, which comprises three phases, has yielded the following results: The predictive approach, first phase of the PAP/CAR method, provides a synthetic map of the distribution of erosive states, with 32.64% of the total area of the catchment area subject to a high degree of erosion and very high. The descriptive cartography of the various forms of erosion, second phase of PAP/CAR, show that this watershed is really affected by erosion in different forms and that 41.09% of the surface be considered as stable or stabilized but with a risk of instability. 3rd phase of PAP/CAR, gives the consolidated PAP/CAR map which shows soil loss in the study area proportional to the increase in the main factors of water erosion. This consolidated erosion map indicates the maximum soil loss in relation to moderately deep ravines located in the northeast of the watershed. The presence of these forms can be linked to the fragile soil and substrate, very extensive agriculture, the steep slope, the aggressiveness of the rains and the absence of plant cover.