Developed barrier island adaptation strategies to hurricane forcing under rising sea levels

Abstract

Global sea levels have risen at a rate of 1.7 mm/year over the last century and are projected to rise an additional 0.2 to 2.0 m by 2100 with some regions experiencing higher rise in relative sea level due to localized processes. As sea levels rise, low-lying, narrow barrier islands are threatened by episodic flooding and wave impact and are particularly vulnerable during storm events. These types of islands are ubiquitous along the U.S. East and South coasts and other coasts worldwide. In this study, we evaluate the effectiveness of several adaptation strategies, including combinations of nature-based and hard structures, on developed barrier islands to hurricane forcing under future sea levels. Interpreting the results of a morphological numerical model, beach nourishment from the toe of the dune to the depth of closure (i.e., active beach only) provides only a slight increase in protection for the island from hurricane forcing as sea levels rise. Raising elevations of the existing dune or existing buried seawall effectively reduces overall volumetric erosion but, under extreme sea level rise, does not protect against bay-side flooding and severe back-barrier erosion. Raising the elevation of the entire island, particularly the back-barrier region, offered the greatest protection from severe erosion on the developed barrier island under future sea level states and hurricane forcing. Using these results, an adaptation pathway based on level of sea level rise is created to illustrate the effectiveness of an adaptive approach in managing the accelerating risk posed by sea level rise.