Hydrologic Dynamics in Response to Natural and Anthropogenic Stresses on a Barrier Island: Saltwater Intrusion and Inundation.

Abstract

The impacts of climate change and sea-level rise on groundwater systems on barrier islands are not well documented in the literature. Globally, there is high competition for useable land in coastal regions because large populations of people live along the coast. If useable land and freshwater resources are lost to saltwater intrusion through sea-level rise or groundwater pumping, coastal communities may experience challenges with meeting high costs of mitigating resulting effects. The goals of this study were to (i) evaluate the impact of sea-level rise and groundwater pumping on saltwater intrusion in the surficial aquifer using an analytical model, and (ii) to evaluate how changes in tidal amplitudes due to sea-level rise may influence groundwater levels in surficial aquifers on barrier islands. To establish if groundwater pumping or sea-level rise has the greatest impact on saltwater intrusion models were used to delineate the location of the toe of the freshwater-saltwater interface as a proxy for the area of the aquifer that was lost to saltwater intrusion. The second objective was to assess the extent of marine and groundwater inundation under different tidal amplitude and sea-level rise scenarios using geospatial procedures. The results show that the percentage of the aquifer occupied by saltwater intrusion due to sea-level rise is greater (51%) than the percentage of the aquifer occupied by saltwater due to consumptive groundwater pumping (34%) for comparable magnitudes of movement of the toe of the saltwater wedge. The results also indicate that when tidal amplitudes are increased by 20%, marine inundation is greater (5%) than groundwater inundation (2%) in the most extreme sea level rise scenario (i.e., 1.5 m of sea-level rise by the year 2100). The results of this study provide estimates of potential changes in groundwater levels that could impact coastal communities and the amount of land that may become impaired. The results can also help water managers understand potential changes to the groundwater system and determine viable solutions to consequences. The relevance of this research is that it will help provide insight on how sea-level rise and groundwater pumping may affect saltwater intrusion and groundwater levels in surficial aquifers on barrier islands.