Optimization of pumping and injection regimes for mitigation of seawater intrusion

Abstract

Seawater intrusion (SWI) stands as a significant challenge impacting coastal aquifers worldwide. The emergence of SWI is a natural phenomenon owing to the density difference between seawater and freshwater. Even without any pumping, the seawater naturally advances inland until a hydrostatic equilibrium between the two water sources is reached. However, human interventions, such as excessive groundwater extraction, coastal developments, and land use as well as climate change intensify the SWI predicament. Efficient solutions to counteract the SWI problem involve the implementation of hydraulic barriers. By employing the Henry problem as a benchmark, the Finite Element Simulator (FEFLOW), which is a numerical modeling software, was used for simulating the flow and transport processes. An integrated FEFLOW-Python code was developed to optimize hydraulic barriers for mitigating SWI. The methodology aims to achieve the maximum possible reduction in SWI by iteratively adjusting the locations and rates of pumping and injection wells. Unlike other investigations, this study explores the utilization of negative SWI barriers to extract brackish water from the dispersion zone and potentially offer a cost-effective alternative water source for desalination plants’ intakes. For the Henry Problem, to maximize the reduction in of SWI, brackish water extraction wells should be situated near the center-bottom of the intrusion zone, with a pumping rate of 2.5 m3/day. For injection wells, the optimal location varies depending on the injection rate (I). Achieving the highest retardation (61%) occurs when the injection rate is 1 m3/day, positioned at the aquifer’s bottom and close to the coastal boundary. However, for injection rates below 0.7 m3/day, the injection well’s optimal location shifts towards the seawater intrusion toe. The choice of injection well location is intricately tied to the injection rate, offering the potential for a maximum retardation of 61%. This study presents a novel approach by establishing explicit correlations for optimizing hydraulic barriers to effectively manage and mitigate SWI.