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.

The Rich aquifer is considered as the biggest alluvial aquifer of the high Ziz basin. However, it faces major natural and anthropogenic pressures include the aridity of the region and development of irrigated areas resulting in the rupture of the hydrodynamic balance sheet and accusing the sustainability of socio-economic fabric by the destocking groundwater reserves.
The piezometry of this aquifer shows that the water flow is converging towards the center at the confluence of the Ziz and Sidi Hamza rivers and in the southern part with some local changing of the flow direction between the observed piezometric states 1980 and 2012.
The development of a 3D finite difference mathematical model, in steady state for 1980, lets us to understand the spatial distribution of permeability, recharge and the hydrodynamic behavior of the aquifer.
This model that confirms the hydrogeological functioning of Rich aquifer system was used to calculate the terms of the water balance which is very balanced.