Control and Modeling of Seawater Intrusion for Conservation of Fresh Groundwater in Coastal Aquifers

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Seawater intrusion is often a major constraint to optimal use of fresh groundwater from coastal aquifers. Excessive groundwater extraction to meet growing demands from an increasing coastal population and the expected rise in mean sea level from global warming will cause seawater to encroach farther inland and threaten the available groundwater supply. In this study, laboratory experiments and numerical analysis were performed to determine the effectiveness of physical barriers and artificial recharge methods to control the seawater intrusion in coastal aquifers. The physical barriers examined were subsurface dams and partially penetrating flow barriers, while the artificial recharge methods included recharge ponds and recharge wells. In the study of subsurface dams, experimental and numerical results show that the residual saltwater trapped in storage areas by cutoff walls is completely flushed out by the freshwater flow from inland.In the study of subsurface flow barriers, we found that saltwater repulsion was linearly related to horizontal barrier location and a third-order polynomial function of penetration depth. For a particular freshwater discharge, this relationship can be used to determine the theoretical saltwater repulsion achieved by subsurface flow barriers of specific depth and location relative to the toe of the intruding saltwater wedge.In the artificial recharge studies, results show that more effective saltwater repulsion can be achieved when recharge is applied near the saltwater toe. Recharge becomes less effective when applied farther and higher from the toe. These findings imply that, for the same recharge rate, recharge wells are more effective than recharge ponds in repulsing saltwater intrusion.