Mapping saltwater intrusion via Electromagnetic Induction (EMI) for planning a Managed Aquifer Recharge (MAR) facility in Maltese Island

Abstract

In coastal areas, saltwater intrusion causes a depletion of the resource by reducing potable and irrigation freshwater supplies and causing severe deterioration of groundwater quality.This trend is observed in Pwales Valley – Maltese Island, where the water resource management plays a crucial role for the environmental sustainability of the area, given the importance of intensive agricultural activity along this valley. In order to tackle such phenomenon, actions or adaptation measures against climate change are strongly required.  For example, Managed Aquifer Recharge (MAR) is an increasingly important water management strategy to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality.For accurately plan a MAR facility, it is crucial to define a hydrogeological model of the studied area, with the use of traditional hydrogeological measurements and innovative unconventional techniques. In recent years, Electromagnetic Induction (EMI) measurements, based on subsurface electrical conductivity data, have been increasingly used for investigating the saltwater intrusion dynamics due to their high sensitivity to the salinity.In the study area of Pwales Valley, a MAR scheme is being planned and, for this aim, a hydrogeological model has been developed through an EMI survey.More than 20,000 apparent electrical conductivity (ECa) data were collected to generate a quasi 3D high-resolution model of electrical conductivity of the Pwales Valley. The results highlighted the spatial extension of the tongue-shape salt water intrusion from east to west along the valley, as well as some geological-hydrogeological peculiarities such as the thickness of the salt wedge and the irregular top surface of the bottom impermeable layer, otherwise undetectable with other techniques. This approach confirms to be a useful tool for an effective hydrogeological characterization, essential for planning mitigation and tackle climate changes actions or adaptation measures, such as a MAR plant.