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 cali-brated 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 manage-ment 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 non- dominated solutions from the Pareto front. The proposed MARS-CEMOGA based saltwater intrusion manage-ment 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 dem-onstrates the efficiency of the MARS meta-model, together with an integrated S–O approach, to solve real-life complex coastal aquifer management problems