Evaluating the efficiency loss of a double-fractured underground dam in coastal seawater intrusion mitigation under groundwater abstraction conditions

Seawater intrusion (SWI) poses a continuing threat to the sustainability of groundwater resources in coastal aquifers, especially in areas where demand for freshwater is high. Among the various engineering approaches, underground dams as physical barriers are commonly used to restrict the inland migration of seawater into coastal aquifers. However, their effectiveness can be significantly affected by structural design and groundwater extraction practices. This research implements the SEAWAT numerical code to investigate the performance of a double-fractured underground dam across changing hydrological conditions. The analysis emphasises the influence of fracture aperture and height, underground dam depth and location and the abstraction well depth, location and abstraction rate. Two representative case studies were analysed: the Henry problem, serving as a benchmark, and the Akrotiri coastal aquifer in Cyprus, demonstrating a real-world case study. The outcomes show that dam efficiency decreases significantly when underground dams are located closer to the seawater boundary, or when dam fractures are positioned close to the base of the aquifer. High pumping rates and a location of the well near the seawater-freshwater interface increase the loss of efficiency, while high saltwater density exacerbates these impacts. The study also demonstrates that dam location has a greater effect on efficiency than its depth. Overall, the outcomes highlight the lack of specific design criteria and strategies for carefully considering groundwater abstraction and the long-term importance of underground dams for coastal groundwater management. The findings provide practical insights for coastal aquifer management, offering guidance for more sustainable utilisation of groundwater resources in vulnerable coastal regions.