Optimization of Concurrent Seawater and Freshwater Pumping from Coastal Aquifers

Covering water demand for secondary uses with resources of inferior quality is already an established practice. In coastal aquifers, saline groundwater can serve as an alternative source. In this paper, we examine concurrent optimization of freshwater and seawater pumping from a coastal aquifer, which may lead to more efficient overall solutions. The particular objective is to determine well locations and pumping rates that meet specified freshwater and saline water demands while preventing seawater intrusion into freshwater wells. A genetic algorithm code is used as an optimization tool, combined with a groundwater flow simulation model based on the Boundary Element Method (BEM). The BEM scheme has a relatively low computational cost and can be efficiently incorporated into the genetic algorithm’s fitness evaluation. Validity of the resulting optimal solutions is further investigated using two, more detailed, groundwater flow and mass transport models: (a) A combination of BEM with a particle-tracking (moving point) technique to simulate seawater movement from the coast towards the wells, and (b) the MODFLOW 6 computational package, including the Groundwater Transport (GWT) model for solute transport. The procedure is illustrated through its application to a synthetic coastal aquifer.