Simulation and Multi-Objective Management of Coastal Aquifers in Semi-Arid Regions

Abstract

Groundwater is the main water resource in many semi-arid coastal regions and water demand, especially in summer months, can be very high. Groundwater withdrawal for meeting this demand often causes seawater intrusion and degradation of water quality of coastal aquifers. In order to satisfy demand, a combined management plan is proposed and is under consideration for the island of Santorini. The plan involves: (1) desalinization (if needed) of pumped water to a potable level using reverse osmosis and (2) injection into the aquifer of biologically-treated waste water. The management plan is formulated in a multi-objective, optimization framework, where simultaneous minimization of economic and environmental costs is desired, subject to a constraint so that cleaned water satisfies demand. The decision variables concern the well locations and the corresponding pumping and recharging rates. The problem is solved using a computationally efficient, multi-objective, genetic algorithm (NSGAII). The constrained multi-objective, optimization problem is transformed to an unconstrained one using a penalty function proportional to constraint violation. This extends the definition of the objective function outside the domain of feasibility. The impact of prolonged droughts on coastal aquifers is investigated by assuming various scenarios of reduced groundwater recharge. Water flow and quality in the coastal aquifer is simulated using a three-dimensional, variable density, finite difference model (SEAWAT). The method is initially applied to a test aquifer and the trade-off curves (Pareto fronts) are determinedl for each drought scenario. The trade-off curves indicate an increase on the economic and environmental cost as groundwater recharge reduces due to climate change.

Evaluation of Analytical Methods to Study Aquifer Properties with Pumping Tests in Coastal Aquifers with Numerical Modelling (Motril-Salobreña Aquifer)

“…The Motril-Salobreña aquifer is one of the few on the Spanish Mediterranean coastline that has of yet shown no signs of marine intrusion in contrast to the usual case for aquifers in semi-arid coastal zones (Kourakos and Mantoglou, 2011;Doulgeris and Zissis, 2014;Zekri et al 2015). Quite the contrary, it shows signs of very active freshwater discharge, as corroborated by the fact that the freshwater-saltwater contact does not penetrate far inland (Duque et al 2008;Calvache et al 2009).…”

A surrogate model for simulation–optimization of aquifer systems subjected to seawater intrusion

“…The majority of previous research on optimal management of SWI considered the simplified sharp interface theory, integrated with optimization tools. However, Qahman et al, (2005;2009), Bray and Yeh (2008), Dhar and Datta (2009), Lin et al (2009), Kourakos and Mantoglou (2011) and Javadi et al (2012) integrate the variable-density models directly with the optimization tools to evaluate different SWI management approaches. The numerical simulation of the variable density hydrogeological system (e.g the coastal aquifer under saltwater intrusion) suffers from computational inefficiency.…”

Optimal management of saltwater intrusion in the coastal aquifer of Malia, Crete (Greece), using particle swarm optimization

“…Thus, in recent years, research has been directed towards heuristic techniques, such as evolutionary algorithms, Tabu search and simulated annealing due to their broad applicability to general management scenarios. Various applications in saltwater intrusion management have applied such algorithms successfully (Cheng et al 2000;Cai et al 2001;Karterakis et al 2007;Mantoglou and Papantoniou 2008;Dhar and Datta 2009;Kourakos and Mantoglou 2011).…”