EVALUATION DE LA VULNERABILITE DES EAUX SOUTERRAINES A LA POLLUTION MOYENNANT LA METHODE P.R.K. : APPLICATION A LA NAPPE PHREATIQUE DU RICH (SUD DU MAROC)/[ VULNERABILITY ASSESSMENT OF GROUNDWATER AGAINST POLLUTION USING THE PRK METHODE : APPLICATION TO RISH GROUNGWATER (SOUTH OF MOROCCO) ]

The assessment of groundwater vulnerability against pollution is a crucial procedure for land settlement. The topography enables decision makers to better manage and analyze information necessary for the delineation and / or identification of areas where groundwater is vulnerable to pollution. Within this context, and considering the strategic role of the Rish groundwater in the socio-economic development of the South East region of Morocco, a map of the aquifer vulnerability with multi-criteria acronym approach PRK has been developed. This approach, based on the parametric methods of class system, aims primarily at designing an index map of the intrinsic vulnerability of the hydrogeological system through gathering the overall indices by classes. It is grounded on the multiplying combination of the information layers relating to three parameters: 1. (P) - topographic slope, 2. the ratio (R) - combining variation of the amplitude of the fluctuations of the piezometric level compared to the thickness of the unsaturated zone and 3. (K) - permeability of the aquifer, whence the generic term P.R.K, taking the initials of these parameters. The overall indexes acquired by this combination vary within a range of values from 2 to more than 91. They are distributed into six classes corresponding to degrees of vulnerability fluctuating from "very less" to "extreme". However, the dominant class is "very less vulnerable". It covers up to 89% of the total area of the studied zone.