Impacts of Climate Change and Urbanization on Groundwater Resources in a Barrier Island

Coastal freshwater aquifers are highly vulnerable to climate change and other anthropogenic environmental impacts. Therefore, managing coastal freshwater for future use requires critical planning. This is especially true for small barrier islands where, in most cases, groundwater could be the only freshwater resource. In this study, the combined effects of climate change, land-use changes, and increased groundwater pumping on freshwater resources of a barrier island were studied. A case study was completed using the field data available for Dauphin Island, a small barrier island located in Alabama, U.S., and by using the simulation data generated from multiple water-resource-management models. Soil and Water Assessment Tool (SWAT) simulations provided recharge estimates under various future land use/land cover and climate-change scenarios. Downscaled global circulation model provided precipitation and temperature patterns for the period 2011-2030. The recharge estimates from SWAT were then used as input in a numerical groundwater model to evaluate saltwater-intrusion effects and forecast the changes in freshwater storage within the island aquifer system. Various groundwater-management scenarios were simulated using the MODFLOW-family computer code SEAWAT to assess the sensitivity of the groundwater system to increased pumping rates and decreased recharge due to climate change and/or future developments. SEAWAT was used to predict the lateral saltwater-intrusion effects and its impacts on groundwater quality and freshwater volume. The simulation results show that the saltwater wedge would advance laterally under all future climate-change scenarios. These results indicate that the shallow unconfined aquifer might not be able to sustain any significant future population growth, especially under adverse climate-change conditions. Analysis of changes in the volume of freshwater lens provided a broader understanding of the coupled effects of climatic and anthropogenic changes on freshwater storage and this information can be used to better manage Dauphin Island's unconfined groundwater system. (C) 2016 American Society of Civil Engineers.