Hydrologic Assessment of the Potential Effects of Sea-Level Rise on Assateague Island National Seashore, Maryland

Assateague Island in southeastern Maryland has been identified as one of the national seashores facing significant risk from the effects of global climate change.  This vulnerability is due to the inherently dynamic and unstable nature of barrier islands, the natural resources present on the island, and to its location in a region experiencing some of the highest rates of relative sea level rise along the east coast of the United States.  These changes will impact use of the island by both humans and fauna; specifically, the island serves as an important breeding ground and habitat for endangered species such as the Piping Plover. The impact of climate change and sea-level rise in particular, is expected to include changes in erosion rates, island morphology, marsh health, and groundwater processes.

 An analysis was conducted of this shallow, permeable, barrier-island flow system to examine the response of groundwater levels and the position of the freshwater/saltwater interface that occur as the elevation of the sea surface increases.   The effects of sea-level rise on this coastal aquifer system were simulated by using SEAWAT, a density-dependent, three-dimensional, numerical groundwater-flow model.  Simulations of sea-level rise were based on projected rates of rise of 6 to 12 mm/yr over the next century.

Results from this analysis suggest that simulated changes in sea level of a meter above present levels will result in substantial changes to the groundwater system including an increase in water-table altitude and increased potential for saltwater intrusion.  Depth to groundwater is an important ecological constraint for wildlife habitat.  Changes in water-table altitude can affect the amount, distribution, and salinity of ephemeral pools, which are important foraging substrates for plovers and other shorebirds, and can affect available food sources through changes in the composition and density of vegetation in the nesting grounds.