Overexploitation and continuous drought effects on groundwater yield and marine intrusion: considerations arising from the modelling of Mamora coastal aquifer, Morocco

This paper studies the effect of drought and pumping discharge on groundwater supplies and marine intrusion. The investigation concerns the Mamora coastal aquifer, northwest of Morocco. A large‐scale groundwater model was established to model (a) the amount of freshwater discharge towards the ocean and the sea water volumes flowing inland as a consequence of the inverse hydraulic gradient, (b) the impact of drought and pumping discharge on the water table level and, as a consequence, on marine water intrusion. In fact, the simulated submarine groundwater discharge (SGWD) would decrease from 864 m 3 /d/km in 1987 to 425 m 3 /d/km in 2000. The simulated volumes of sea water intruding the aquifer as a result of inverse hydraulic gradient would increase from 0·25 Mm 3 /y in 1987 to 0·3 Mm 3 /y in 2000. As a consequence of a negative rainfall gradient of −5 mm/y, the simulated SGWD would decline to 9 m 3 /d/km and the sea water intrusion (SWI) would increase to 0·35 Mm 3 /y since the year 2010. Due to insufficient data on the trend of pumping discharge, a hypothetical increase of this latter from 38·3 Mm 3 /y to 53·2 Mm 3 /y is simulated to induce an increase of marine water intrusion from 0·25 Mm 3 /y to 0·9 Mm 3 /y. Consequently, to optimally exploit this seemingly fragile coastal aquifer, a plan of future actions to implement is proposed.