MAPPING OF SOIL WATER EROSION BY REMOTE SENSING AND GIS: CASE OF THE WADI BOUMESSAOUD WATERSHED (NW-ALGERIA)

Abstract

Like other semi-arid regions, the north of Algeria undergoes the impact of a strong erosive potential especially in the denuded lands of steep slopes. The climate with all its hazards favored the occurrence of intense downpours and torrential floods, thus generating several environmental damages such as the loss of agricultural land, the siltation of dams and water pollution. The identification of areas at risk of water erosion is therefore necessary, this leads us to resort to cartographic approaches using various digital data which will be subjected to a multifactorial analysis via the computer tool of the GIS. The methodology adopted is that which is inspired by qualitative models using a crossing of parameters representative of the determining factors in erosion in the form of logical combinations. First of all, the factors intrinsic to the soil (relief, type of soil and vegetation cover) are combined with each other to obtain an index identifying the potential sensitivity of soils to erosion, then a cross-referencing is carried out with the climate factor by the effect of precipitation erosivity. The study applied to the Wadi Boumessaoud watershed (118 km²) located in the northwest of Algeria, enabled us to draw up a map describing four classes of multifactorial risk of soils to water erosion: low (26%), medium (35%), strong (28%) and very strong (11%). The results indicate that the basin is subject to strong and moderate erosion affecting more than 60% of the total surface, where the erosion factors combine with each other: steep slopes exceeding 15°, degraded plant cover and soils characterized by particularly soft and strongly erodible outcrops undergoing extensive agriculture. The study could constitute a reference document for the forecasting of floods and the protection of irrigated perimeters or any other anti-erosion development project to be planned.