Large scale modeling of seawater intrusion in a coastal aquifer: application to the North Sharon and Heffer Valley areas, Israel.

Abstract

Seawater intrusion, in the form of a wide transition zone from fresh water to seawater, is a well-known phenomenon occurring in most coastal aquifers, as a result of unbalanced freshwater extraction practices. The prediction of seawater intrusion resulting from planned water extraction scenarios is of crucial importance as it allows maximization of freshwater sustainable extraction, while preserving the coastal aquifer's viability by minimizing adverse salinization processes. Seawater intrusion can be monitored by observation wells. However, the number of such wells needed for the construction of a reliable three-dimensional picture of the transition zone between fresh water and seawater would be so large that it is practically infeasible. Therefore, simulation models are used, in combination with the available observed data. This work presents the development, application, and validation of a three- dimensional model, FEAS, for the simulation of seawater intrusion, formulated as a density dependant groundwater flow and salt transport problem in 3-D heterogeneous and anisotropic formations. FEAS was applied to the North Sharon – Heffer Valley region of the Israel coastal aquifer. This is a heterogeneous anisotropic aquifer, covering an area of over 300 km2. The model was first calibrated to identify the values of its hydraulic parameters (hydraulic conductivity, porosity, specific yield, and replenishment coefficients). It was then run for flow and salt transport for three time periods: 1) 1800-1933, pristine conditions (prior to any pumping), in order to obtain a picture of seawater wedge prior to the aquifer exploitation; 2) 1933-1974 rapid development of pumping from the aquifer, and 3) 1975-2002 current conditions, with significant sea water intrusion. The results obtained at the end of the simulation periods were in satisfactory agreement with the available data. The model was then used for estimating the impact of a number of exploitation and replenishment scenarios.