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Mapping the Zone: Improving Flood Map Accuracy
FIGURE 5.4 Aerial photograph of the coast near Biloxi, Mississippi, showing the layout of one-dimensional WHAFIS transects (red lines). SOURCE: Courtesy of David Divoky, HSMM/AECOM. Used with permission.
include development of better hurricane ensemble parameters, more accurate estimates of the return period of storms in several coastal regions, more accurate simulations of storms surge and estimations of SWEL in Louisiana and Mississippi, and increased use of very fine, unstructured grids (100 meters or less) to resolve complex coastal terrains and enable the use of high-resolution lidar (light detection and ranging) data.
FEMA (2006b) recommended merging developments in hydrodynamic and statistical methods with established methods for wave analysis, erosion assessment, and flood hazard mapping. However, coupled 2-D surge and wave models are not yet fully integrated into mapping practice because 2-D wave models “do not incorporate bottom friction and obstruction effects of the sort considered by WHAFIS” and FEMA has not developed guidelines for 2-D overland wave modeling (FEMA, 2008b). Recent applications of coupled 2-D surge and wave models have demonstrated their ability to calculate wave setup and wave crest (Sheng and Alymov, 2002; IPET, 2008).
In Louisiana, Mississippi, and North Carolina, novel approaches to coastal flood mapping are either under way or have recently been completed. These new coastal mapping studies are the first to replace FEMASURGE with the ADCIRC model and could be used as part of a more comprehensive assessment of methods for enhancing mapping—for example, by gathering more data for verifying wind, storm surge, and wave models (see below).
FROM MODELS TO MAPS: DEVELOPING THE NEXT GENERATION OF COASTAL FLOOD MODELS
Coastal flood models—and by extension, coastal flood maps—will continue to be improved in the coming decades, driven by the increased availability of high-resolution topographic data and more sophisticated models. This section identifies opportunities to improve the accuracy of coastal flood models and recommends ways to guide the development of the next generation of coastal flood models and maps.