Assessment of the risk and extent of seawater intrusion using geophysical techniques and vulnerability models: case of the coastal aquifer of Souss-Massa, Morocco

Abstract

Groundwater resources represent one of the main pillars of socio-economic development in the Souss-Massa region, an important producer of fruits and vegetables in Morocco. However, the quality of groundwater resources is degraded due to drought, lack of aquifer recharge, and over-pumping which increase the risk of seawater intrusion. The latter threatens the coastal aquifer of Souss-Massa. Hence, a detailed study is needed to explore the extent of seawater intrusion and to identify its most vulnerable sites. To fulfill this objective, geophysical investigations (SMD-TEM) and an improved GALDIT index were used. In addition, groundwater quality index (GQI) and vulnerability maps were combined to generate a risk map of seawater intrusion. The results show that seawater intrusion reaches 2500 meters from the coast, and its depth is around -35 meters above sea level. Moreover, improved GALDIT divided the study area in five classes, showing high and very high degrees in the coastal fringe and along the two rivers of Souss and Massa. Furthermore, our risk map indicates three level of risks, with the highest levels recorded in the south-west of the coast, namely in Tifnit, Douira, and Sidi R’bat. A typical management strategy plan was proposed to ensure the protection and sustainability of groundwater resources for current and future uses. The proposed methodology could be applied in similar contexts and can be adapted to the specific hydrogeological conditions.