Simulating storm surge waves for structural vulnerability estimation and flood hazard mapping

Wave action during storm surge is a common cause of building damage and therefore a critical consideration when estimating structural vulnerability and mapping flood risk. Traditional depth-damage curves, however, relate building vulnerability solely to inundation depth and therefore neglect an important damage mechanism. Similarly, flood mapping studies typically emphasize expected inundation rather than wave conditions. In this study, we consider the impact of wave effects on vulnerability estimation and flood mapping using a pair of hydrodynamic models (ADCIRC + SWAN and BOUSS1D) to simulate inland storm surge flooding. The models are used to simulate flooding in a heavily impacted coastal community (Ortley Beach, New Jersey) during Hurricane Sandy (2012) and to estimate inland hazard parameters characterizing inundation, wave and velocity effects. To quantify structural vulnerability, fragility curves are developed by statistically relating the simulated hazard parameters to surveyed building damage. The results indicate that dynamic hazard characteristics such as significant wave height are the dominant predictors of severe structural damage. The flood simulation is also used to map the variation of surge and wave effects in the community. Comparing this analysis to flood zones delineated by the Federal Emergency Management Agency in the community's Flood Insurance Rate Map reveals severe wave action and building damage in a significant portion of the community deemed least exposed to flood impact. It is suspected that this misrepresentation of risk resulted from overconfidence in the performance of the community's frontal dune under severe surge and wave actions.