Abhatoo - Centre Nationale de Documentation

Landlocked in the Western High Atlas (WHA), the watershed of the Issen river with a surface area of 1300 Km² is subject to a worrying erosive potential, source of fine sediments responsible for the silting of the Abdelmomen dam. The objective of this work is to map the potential erosion at the scale of this large sub-basin on the right bank of the Oued Souss using the silting rate and an empirical model of soil loss and the Geographic Information System (GIS). The bioclimatic synthesis shows a spatio-temporal variation in rainfall and vegetation under a medium arid to upper semi-arid climate. The rainfall erosivity index R shows a high variability ranging from 26 to more than 120 MJ.mm/ha.h.yr in the most watered areas. Soil erodibility K varies from 0.15 to 0.81 t.ha.h/ha.MJ.mm with a calculated average of 0.43 and more than 60% of the soils are highly erodible. The entire basin is located on relatively steep terrain, the value of the topographic factor LS ranges from 0 to 470 which reveals a contrast in morphological forms. The potential erosion rate is 164 tons/ha/year on average, equivalent to an actual loss of more than 21 million tons/year. Thus the specific degradation at the Abdelmomen dam is of the order of 646 m3/km²/year. This study thus makes it possible to evaluate the rate of soil losses and to predict the alarming potentialities of the land for water erosion which can occur at the level of the said basin.