Coastal Groundwater Systems
Changes in climate and sea level will drive changes to the coastal groundwater system that will impact both human populations and coastal ecosystems. Increases in sea-level will raise the fresh water table in many coastal regions (figure GW1). Impacts to humans may include an increase in the potential for basement or septic system failure. Sea-level rise can also contaminate groundwater supplies due to landward and upward movement of sea-water in coastal aquifers. The intrusion of saltwater into groundwater systems will also impact coastal ecosystems such as marshes by changing the elevation of the freshwater-saltwater interface.
A major concern for water managers is the potential adverse effect of sea-level rise on the depth to the freshwater-saltwater interface near public groundwater supply wells. Pumping from public-supply wells in coastal aquifers underlain by saltwater can lower the water table with respect to sea level, decreasing the depth to the freshwater-saltwater interface beneath the pumping well. This increases the potential for saltwater intrusion, and potentially limits the amount of potable water available from the well.
Understanding how sea-level rise may impact the groundwater hydrology in shallow, unconfined coastal aquifers such as those occurring on barrier islands is important when assessing potential impacts on the sustainability of coastal habitats like salt marshes.
This project is currently focused on developing a calibrated three-dimensional ground-water flow model capable of simulating both the fresh and saltwater flow systems on Assateague Island and collecting the hydrogeologic data necessary to calibrate and evaluate the model (figure GW2). These data will be used to conduct a sensitivity/uncertainty analysis for different climate change and sea-level rise scenarios. These scenarios will be combined with the model uncertainty (estimated using the field calibration data set) to estimate probabilities of ecosystem health relevant to Piping Plovers and other assets located within the boundaries of our study (e.g., other habitat and park infrastructure elements). Results from the hydrogeologic analyses will be integrated with related predictions of island erosion, overwash and inundation and marsh resilience developed by other parts of the overall project using a Bayesian Network. The network will be used to evaluate information to inform the decision making process. Decision makers should therefore be able to focus their limited resources where they are most likely to maximize effectiveness. The quality of the forecasts should improve as fundamental knowledge of coastal systems is incorporated into these assessments.