The Delaware Geological Survey released a new Report of Investigations Number 83 titled “Evaluating Impacts of Sea-Level Rise on Groundwater Resources in The Delaware Coastal Plain” which was prepared by Changming He and Thomas E. McKenna of the Survey. DGS RI No. 83 documents a method that uses numerical models and GIS spatial analyses to study how a rise in sea level causes changes in Delaware’s coastal groundwater levels and salinity. These changes, in turn, impact land use.

Sea-level rise is a major concern for the coastal area. It leads to a rise of the water table to a shallower depth, salinization of aquifers, wetland drowning, coastal erosion, and salinization of agricultural soils. Due to low elevation and a shallow water table, the Delaware Bay coast is highly vulnerable to sea-level rise. To quantitively evaluate the impacts of sea-level rise on water-table depth and salinity changes in the surficial aquifer, the researchers built a synthetic groundwater flow model using SEAWAT4 software, a three-dimensional, variable-density groundwater flow model. The conceptual model is based on the characteristics of ten Delaware Bay watersheds, including the sizes of watersheds, lengths of rivers, and salinity distribution patterns. For land use impact analysis, the simulated water-table depths were transferred to the real-world watersheds by mapping model coordinates to a curvilinear grid system within each watershed.

Three scenarios of sea level rise (0.5m, 1.0m and 1.5m by 2100) were simulated. Impacts from changes in water-table 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). The authors identified areas adversely impacted by sea-level rise by comparing modeled water-table depths to the critical depths. The simulation results predict that sea-level rise may cause significant impacts by year 2100 from a rising water table. Over 60 percent of the impacted areas were cropland. The model results also indicate that the saltwater front in the aquifer under a riverbed migrates landward to as much as 4.8 kilometers from the initial location at the marsh/upland boundary. The salinization is limited to a small area near and parallel to river and marsh boundaries.

The report fulfills part of the DGS’s mission to understand hydrologic systems and to advise, inform, and educate Delawareans about the results of such investigations so they can serve as a resource for scientists, engineers, planners, emergency managers, and the public.

Report of Investigations No. 83 is available in pdf format from the DGS web site at http://www.dgs.udel.edu/publications. For additional information, contact the Survey at (302) 831-2833 or via email at delgeosurvey@udel.edu.