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Title: MULTI-OBJECTIVE MANAGEMENT OF COASTAL AQUIFERS IN SEMI-ARID REGIONS UNDER DROUGHT CONDITIONS

Author: G. Kourakos and A. Mantoglou

Year: 2009

Publisher: European Water Resources Association (EWRA)

Description:

Groundwater is the main water recourse 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 in the island of Santorini. The plan involves: i) desalinization (if needed) of pumped water to a potable level using reverse osmosis and ii) 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 determined 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.