Optimal design of measures to correct seawater intrusion

Abstract

Numerous studies have been devoted to the optimization of groundwater management strategies in coastal aquifers. However, little has been done to address the problem of initially contaminated aquifers, the subject of this paper. Corrective measures need to be optimally designed to improve water quality while minimizing changes in the existing pumping regime. To this end, we compare two optimization methods. The first one is linear and consists of maximizing pumping rates while constraining heads to prevent seawater inflow. The second one consists of minimizing the changes from current pumping rates, so as to preserve existing rights, while constraining concentrations, which leads to a nonlinear programming problem. In both cases, corrective measures include a reduction in pumping rates, inland artificial recharge, and a coastal hydraulic barrier. Not surprisingly, the nonlinear problem leads to a more efficient solution, both in terms of pumping rates and actual cleanup of the aquifer. Nevertheless, the linear formulation yields insights into the optimal allocation of pumping. More importantly, the linear formulation enables us to readily calculate the hydraulic efficiency (gain in pumping rate per unit increase in recharge rate) of corrective measures. The fact that efficiency is consistently greater than 1 proves that the hydraulic barrier not only increases resources but also protects the existing ones. Therefore we conclude that both optimization approaches are useful and should be used.