Integrative management of saltwater intrusion in poorly-constrained semi-arid coastal aquifer at Ras El-Hekma, Northwestern Coast, Egypt

International audienceSaltwater intrusion is a major concern in coastal aquifers, particularly in arid and semiarid regions, where recharge is limited and groundwater withdrawal is the main source of potable water. In Ras El Hekma groundwater occurs in the Pleistocene aquifer as a thin lens of freshwater where groundwater quality is very sensitive to pumping stresses. High groundwater withdrawals from the Pleistocene aquifer deteriorate the groundwater quality along the coast due to upwelling of saltwater into the thin lens freshwater. The Pleistocene aquifer is poorly-constrained; the hydrological and geochemical records are sparse. Therefore, a simple analytical approach has been used in order to address local and regional groundwater management issues, for cases of data scarcity using little known and well defined parameters. The model assumes steady state flow as an initial condition in an isotropic and homogeneous medium, with a sharp interface between the freshwater and seawater wedge. The model combines the hydrogeological and geochemical characterization, adapted to the aquifer geometry, in order to provide global salt and freshwater balances to the Ras El Hekma scale site. The model shows progressive extension of the seawater intrusion zone (x-toe) upon increasing the groundwater withdrawals from 250 m3/day to an order of magnitude of this amount. The x-toe distance has been extended from 1700 to 5000 m from the tip of Ras El Hekma to inland. Such model could be applied to estimate the volume of the freshwater and seawater wedge along the coast as well as to predict the groundwater withdrawals under different pumping scenarios. Seawater intrusion, in the Ras El Hekma area, is caused by the unbalance between the pumping withdrawal rates and the natural recharge from precipitation. The model can be applied for similar hydrogeological systems, specifically, coastal aquifers located in semiarid to arid environments where limited aquifer data is available