Three-Dimensional Mapping of Seawater Intrusion Using Geophysical Methods

Seawater intrusion is a common problem in almost all coastal aquifers. However, the degree of intrusion may differ from one aquifer to another depending on many factors including, among others, geometric and geological conditions of the coastal aquifer, hydrological parameters, climatic conditions, pumping rates and recharge events. Proper assessment and mapping of the groundwater quality and transition zone in coastal aquifers are needed for any groundwater management in coastal aquifers. Geophysical methods represent a feasible tool for the monitoring and assessment of seawater water intrusion problems in coastal aquifers. This paper presents earth resistivity surveys that have been conducted in the coastal aquifer of Wadi Ham in United Arab Emirates. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus improve the interpretation of earth resistivity imaging data. Results of 2D earth resistivity imaging surveys and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. A three-dimensional mapping of the seawater intrusion transition zone was developed through the integration of two-dimensional vertical resistivity profiles. The paper demonstrates the feasibility and accuracy of geophysical methods in three-dimensional mapping of seawater intrusion problems.