Optimal Locations of Groundwater Extractions in Coastal Aquifers

A regional water supply management model for coastal aquifers was developed. One of its outcomes is the definition of the optimized locations for groundwater withdrawal. Such a tool permits the analysis of alternative plans for groundwater extraction and the sustainable use of water resources in a coastal aquifer subject to saltwater intrusion. The principal components are the evolutionary optimization and the analytical/numerical simulation models. The optimization technique looks for the best well locations taking into consideration the economic results and the satisfaction of the societal water demand. However these two concerns are conditioned by trying to control the saltwater intrusion, i.e., preserving the environmental equilibrium. The simulation model uses the governing mathematical equations for groundwater movement to find the interface between freshwater and saltwater. Because of the non-linearity in the system and the possibility of a jumping interface, a security distance was defined. This is a controlling variable which can be set by the decision makers. The model was applied to a typical case with interesting results. For example, diagrams showing the relationship between the location of the wells and the security distance(s) are of importance to the managers. It was also crucial to have an understanding of the tradeoffs between groundwater withdrawals, positions of the wells from the coast line, and the security distance. The model was also applied to a real case in order to relate the extractions, distances and artificial recharge (not presented in this paper).