EFFECT OF ZERRAR DAM ON THE AQUIFER SYSTEM OF ESSAOUIRA BASIN (MOROCCO)

The strong growth in water demand in North Africa pushed the government to build more dams to increase the availability of water resources, naturally limited, and cope with the strong temporal irregularity (seasonal and interannual) of precipitation. The Morocco has 140 large dams with a total capacity of 17 Gm3. However, the amount of potential fresh water is decreased by siltation of dams estimated at 70 million m3, surface evaporation and water loss by the banks and foundations. We are witnessing strong disparities from one site to the other and a significant increase in erosion in some basins in recent decades, especially the Rif where siltation of dams is terrible and make null and void any new dam location. This represents a reduction in capacity of 0.85% year -1 . The last dam dredging techniques is estimated at 5 euros for cubic meter, well above breakeven per cubic meter produced by desalination of sea water (1 euro). The Zerrar dam of Essaouira Basin, object of this study, illustrates this problem, in addition to salinization phenomena observed in the two aquifers in the synclinal basin caused by the mobilization of resources. The implementation of Zerrar dam has significantly altered the hydrology of the basin, particularly at its downstream. All points show a lowering of the water level, this trend is the result of the effect of Zerrar dam and climate change, in addition to over-exploitation. The aquifer system then having an average to poor potability result of the immediate effect of the dam that regulates the flow of the Ksob Wadi, feeding the aquifer system.