Identifying Potential Sea-Level Rise Impacts to the U.S. Mid-Atlantic Ocean Coast: Results from a Panel Assessment

The ability to reliably predict changes to coastal landforms such as beaches and barrier islands in response to sea-level rise is limited by the scientific understanding of the many factors and processes that contribute to these changes. In addition, there is not a clear consensus regarding the utility of existing conceptual, analytical, or numerical models to forecast these changes over 50-100 year time scales. To assess potential sea-level rise impacts to coastal landforms in the U.S. mid-Atlantic region, a panel of coastal scientists with extensive professional experience in the region was convened to develop a qualitative assessment of future coastal changes that may occur. Using criteria derived from published work, the mid-Atlantic coast was divided into four geomorphic types: spits, headlands, wave-dominated barriers, and mixed-energy barriers. A range of potential coastal responses was identified for each geomorphic type based on three principal sea-level rise scenarios. The scenarios assumed that: a) the long-term relative sea-level rise rate (~3-4 mm/yr) observed over the 20th century would persist through the 21st century, b) the 20th century rate would increase by 2 mm/yr, and c) the 20th century rate would increase by 7 mm/yr. The panel acknowledged that coastal engineering practices could be employed to mitigate erosion but it was uncertain if these would persist into the future. In addition, storminess was assumed to increase. Potential responses to these sea-level rise scenarios depend on the landforms that occur within a region and include increased likelihood for erosion and shoreline retreat for all coastal types; increased likelihood for erosion, overwash, and inlet breaching for barrier islands; as well as an unexpected suggestion that some barrier islands could cross a geomorphic threshold. Systems that cross a threshold are thought to exhibit more dramatic responses such as barrier island narrowing, more rapid migration, or become segmented.