Modelling and management of saltwater intrusion in a coastal aquifer system: A regional-scale study

Increasing saltwater intrusion in the Barguna aquifer due to unplanned groundwater abstraction is a concern for the people of Barguna district, Bangladesh. A sustainable groundwater abstraction strategy capable of confining saltwater concentrations in the aquifer within acceptable limits is required for the Barguna aquifer system. In this study, a regional-scale integrated simulation-optimization (S-O) approach was used to prescribe an optimal groundwater abstraction strategy for the aquifer. The flow and transport processes were simulated by a calibrated and validated numerical simulation model using the available hydrogeological data. The simulation model was then used within the integrated S-O based management model to evolve ideal groundwater abstraction patterns to restraint saltwater intrusion in the study area. Computational efficiency of the management model was achieved by using a Multivariate Adaptive Regression Spline (MARS) based meta-model emulating the density dependent salinity transport processes of the study area. The developed MARS-based emulators were then externally linked with a Controlled Elitist Multiple Objective Genetic Algorithm (CEMOGA) as a replacement of the numerical model. The study area comprised of a set of production wells for abstracting groundwater for beneficial purposes. Barrier extraction wells placed along the coastline were also considered as a management option to control saltwater intrusion hydraulically. Grey Relational Analysis was utilized as a quick decision-making tool for selecting a relatively better solution from a large number of nondominated solutions from the Pareto front. The proposed MARS-CEMOGA based saltwater intrusion management methodology was capable of obtaining accurate solutions for optimal groundwater abstractions from a combination of production and barrier extraction bores in a real-life coastal aquifer system. This study demonstrates the efficiency of the MARS meta-model, together with an integrated S-O approach, to solve real-life complex coastal aquifer management problems.