Evaluating Impacts of Sea-Level Rise on Groundwater Resources in The Delaware Coastal Plain

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Newark, DE: Delaware Geological Survey, University of Delaware
Due to low elevation and a shallow water table, the Delaware Bay coast is highly vulnerable to sea-level rise. Numerical simulations of rising sea levels, groundwater flow, and salt transport through year 2100 indicate significant impacts on land use due to a rising water table and localized impacts due to saltwater intrusion in the surficial aquifer. Impacts from changes in watertable depths were defined as the conditions where the water table rose above two critical depths: 0 meters (termed saturation, waterlogging, or inundation) and 0.5 meters (effective rooting depths of major local crops). Scenarios modeled were for 0.5, 1.0, and 1.5 meters rise by year 2100. Simulations used SEAWAT4, a three-dimensional, variable-density groundwater flow model. We constructed synthetic conceptual and numerical models with a single rectangular-shaped watershed with an upland, one river, and bay-parallel and inland salt marshes. Parameters for the models were based on the characteristics of ten Delaware Bay watersheds. We transferred water-table depths from simulations to real-world watersheds by mapping model coordinates to a curvilinear grid system within each watershed, which allowed for comparison of areas adversely impacted by sea-level rise by comparing water-table depths to the critical depths. The simulation results predict that sea-level rise causes significant impacts from a rising water table by year 2100. Over 60 percent of the impacted area in all scenarios was cropland. The model results also indicate that the saltwater front under the riverbed migrates landward as far as 4.8 kilometers from its initial location, but is limited to a small area near and parallel to the river and marsh boundaries.
Delaware Bay, MiMid-Atlantic Coastal Plain, Mid-Atlantic coast, groundwater modeling, saltwater intrusion, sea-level rise, groundwater, surficial aquifer, Holocene