19 Quantifying Coastal Vulnerability to Geohazards: Methods, Results, and Recommendations

Friday, 13 March 2009
1:30 PM - 5:30 PM

A NATIONAL ASSESSMENT OF BARRIER ISLAND VULNERABILITY TO EXTREME COASTAL CHANGES DURING HURRICANES

Paper number: 19-3
Program: Theme Sessions
Time: 2:10 PM – 2:30 PM

Authors

Abstract

Along much of the East and Gulf Coasts of the United States, hurricanes have been responsible for some of the most dramatic changes to our coastal environments – from the creation of large overwash deposits to the opening of new inlets. Strong winds associated with these tropical storms bring large waves and storm surges that force significant changes on fragile barrier islands. The spatially variable coastal response to storms is dependent, in part, on the interactions between longshore variable pre-storm beach morphology and offshore physical forcing. By comparing the relative elevations of barrier-island morphology and storm-induced water levels, the potential vulnerability of our Nation's barrier islands to extreme coastal change during hurricane landfall is defined.

The vulnerability of Gulf and southeast Atlantic barrier-island beaches to erosion, dune retreat, overwash, and inundation during a direct hurricane landfall is assessed by comparing the elevations of storm-induced water levels (storm surge and wave runup) to the elevations of the crest of the primary sand dune that defines the beach system. Storm-induced mean-water levels for Category 1-5 hurricanes are calculated as the sum of SLOSH-modeled storm surge and parameterized wave runup, based on SWAN models of maximum wave height for each category storm. Dune elevations are measured every 20 m along the coast with lidar surveys of beach topography. Maps detailing the predicted water levels, measured morphology, and expected coastal change for each category storm can be used by coastal managers to determine the relative vulnerability of barrier islands and to assess areas of a coastal community that are more susceptible to extreme storm-induced changes such as overwash and inundation.