A Methodology to Analyse and Assess Pumping Management Strategies in Coastal Aquifers to Avoid Degradation Due to Seawater Intrusion Problems

In this paper we will focus on an interesting and complex problem, the analysis of coastal aquifer management alternatives in aquifers affected by seawater intrusion problems. A systhematic method based on an approximation of the safe yield concept for coastal aquifers and a simple model approach to the problem is proposed to help in the decision making process. It is based on the assessment of an index, that we have called the Pumping Reduction to Achieve a Natural Good Status (PRANGS), which we have defined as the minimum reduction in pumped abstractions necessary to maintain seawater intrusion below the value estimated for the natural regime under different climate conditions: humid (PRANGS_h), intermediate (PRANGS_i) and dry years (PRANGS_d). It requires to solve an optimization problem (for each of the climate conditions: humid, intermediate and dry years), whose objective function is to minimize the reduction in pumping whilst ensuring intrusion does not exceed the natural regime ones. A simulation model that provides a valid approximation of seawater intrusion is needed. The methodology was applied to a well-known Spanish Mediterranean aquifer, the Oropesa-Torreblanca Plain aquifer. The optimization problem was solved using an iterative process from a constant density flow simulation model of the aquifer, assuming a direct relationship between piezometric drawdown and seawater intrusion.