Study of intrinsic vulnerability to the pollution and quality of surface water in the Saharan zones: Example of wadi Rheris basin (Southeast Morocco) [Etude de la vulnérabilité intrinsèque à la pollution et qualité des eaux de surface dans les zones arides: Cas du bassin versant de l'oued Rhéris (Sud-Est du Maroc)]

The surface water resources are increasingly threatened by pollution,therefore,degradation of water quality is growing because the human activity is increasing. the agricultural,urban and industrial activities have contributed in recent decades to increase the potential for contamination of surface water. to avoid further water contamination problems,it is essential to better understand the resource with the aim of protecting it. for this purpose,it is necessary to take all measures to ensure water quality particularly in saharan zones,marked by the scarcity of surface water (example of wadi rheris basin). the mapping of intrinsic vulnerability of surface water resources in the rheris basin is an important tool for making decision and allows us to identify different classes of vulnerability across rheris basin. the method followed,it is based on the processing and exploitation of data,such as slope,the river orders,permeability,runoff,drainage density,etc. the integration of all these data in a geographic information system (gis) environment ensures detailed mapping parameters that determine the vulnerability to pollution in rheris watershed. the results show that the middle class of vulnerability is the most dominant; it represents 52% of the basin area,followed by low vulnerability areas by 31%,but the high and very high vulnerability extend over an area of 2123 km2,which corresponds to 16.7%.