CAN GEOMORPHIC CONTROLS OF HURRICANE DAMAGE BE QUANTIFIED FOR A KATRINA-SIZE STORM?

Coastal hazard mapping has historically been based primarily on simple models of storm inundation (SLOSH model), erosion rates, or estimated setbacks from a control line. There is still only a rudimentary understanding of how the numerous geomorphic attributes of a particular stretch of shoreline control cross-shore storm energy. A series of hurricane hazard maps for a variety of coastal settings have been made based largely post-storm field investigations after several hurricanes between 1980 to 1999, and using the observed damage patterns to qualitatively predict the potential for damage from subsequent storms in similar settings. More recently, attempts at hindcasting storms to quantify geomorphic controls on damage patterns were deemed successful for Hurricanes Hugo (1989), Opal (1995), Georges (1998), and Fran (1999).

Regression analysis after Hurricane Katrina (2005) revealed that site elevation provided the best protection followed by dune height (in front of the site) and beach width. However, Katrina's observed damage patterns did not seem to correlate as well as other storms with pre-storm conditions. Those findings actually make sense because the entire premise of our mapping approach is that virtually all coastal areas are at extreme risk hurricane generating significant storm surge, as did Katrina. Our original observations were based largely on the hazards of hurricanes generating lower storm surge of more limited extent.

As a result of the preliminary Katrina study, a revised regression analysis was performed extending the study area farther inland and including a longer stretch of coast to include geographic areas experiencing a broader range of storm surge levels We also included wind damage and inland flooding patterns and areas of impact with higher versus lower slopes and higher elevation. By doing this, we covered a large enough area so that pre-storm geomorphic conditions varied enough to elucidate correlation with observed damage patterns.