HISTORICAL RECORDS OF STORM-INDUCED BEACH AND DUNE EROSION: APPLICATIONS TO COASTAL HAZARD IDENTIFICATION AND MAPPING

While there is debate in the scientific literature as to whether or not storms contribute to long-term shoreline change, there are numerous storms observed in the 20th century that have, in a matter of hours or days, caused shoreline retreat and dune erosion equivalent to several decades of “background” shoreline change. Although considerably less well documented than the storm-induced erosion, researchers have observed a period of post-storm beach and dune recovery based on the seaward migration of the shoreline or changes in beach profile (e.g., Hurricane Alicia in Texas; Ash Wednesday Storm of 1962 in Delaware). Further, a recent analysis of the impacts of the Ash Wednesday nor’easter along the mid-Atlantic Coast has revealed considerable spatial variability in the shoreline’s response to this storm. These results include a comparison of the surge penetration distance (Morton and Sallenger, 2002) and the degree to which the 1962 post-storm shoreline position may be statistical outlier from other shorelines in the historical database.

As the best-available technical resources, historical shoreline positions and topographic/ bathymetric profile data are used for a variety of engineering and management purposes, including the design of beach restoration projects and the identification of erosion hazard areas. An historical record of the performance of sand dunes along the U.S. Atlantic and Gulf coasts and the Dutch coast of the North Sea were used by the Federal Emergency Management Agency (FEMA) in 1989 to propose a geometric model of storm-induced erosion for use in coastal flood hazard studies. In this approach, the ability of a primary dune to withstand the 1%-annual-chance (100-year) storm surge (and thus provide some protection to structures located landward) is dependent on the pre-storm, cross-sectional area of the dune. In addition to presenting FEMA’s storm-induced erosion methodology, which is currently applied along the open coast from Texas to Massachusetts, this paper will challenge session participants to identify existing studies or datasets (e.g., pre-/post-storm LIDAR, swath bathymetry, nearshore profiles) that may be of use in evaluating (and possibly refining) the methodology, its assumptions, or its application in different geomorphologic settings.