Management Model for Conjunctive Use of Coastal Surface Water and Ground Water

Abstract

A nonlinear multiobjective management model has been developed for managing water use within a coastal region. Two conflicting objectives are considered: cost-effective allocation of surface water and ground water supplies, and minimization of saltwater intrusion. Optimal control of the system is examined by studying the response of these objectives to changes in ground water pumping rates and transfer of surface water between sources and users. System constraints include economic, operational, and institutional requirements. The objectives, some of the constraints, and the ground water flow equations are formulated as nonlinear functions of the decision variables. The flow model simulates the flow of ground water using a quasi-three-dimensional finite-difference model based on the sharp interface assumption. The nonlinear optimization problem is solved with MINOS. The flow simulation and the optimization model are considered simultaneously by linking the simulation directly into the optimization procedure. The multiobjective aspect of the problem is solved using the constraint method. To test the methodology, a hypothetical case study based on the Waialae aquifer of Hawaii was developed and examined.