Mortality during Hurricane Sandy: the Effects of Waterfront Flood Protection on Staten Island, New York

Hard defenses, such as levees or land berms, are often considered the most effective approach to reduce flood risk. This study reveals a potential increase in mortality when hard protections cannot defend a location against low probability but high cost events. Staten Island, New York suffered devastating damage from Hurricane Sandy, including 23 fatalities. Eighteen of these fatalities occurred on the East Shore, which was protected by an elevated berm that kept the neighborhood free of seawater for several decades. This study demonstrates that the berm may have contributed to the concentration of fatalities in the area by increasing the speed at which seawater rose within the neighborhood, causing some people to be trapped in places where they could not escape rising waters. The study uses the hydrodynamic model ADCIRC to simulate Hurricane Sandy flood conditions, providing water depth, the water rise rate, and water velocity. Statistical analyses show that the rise rate is the only variable whose effect on the presence of a fatality in a given location is statistically significant, while other flood characteristics and socio-economic factors are not. A model experiment that examines flood conditions in the presence of a lower discontinuous berm that historically existed at the location in Midland Beach finds that the increased height and continuity of the berm worsened the water rise rate during Sandy by 54%, and the logistic regression suggests that this results on average in a 249% increase in probability of mortality. The potential increase in mortality risk needs to be taken into account when designing coastal protections for locations where the most extreme floods can be sufficiently high that protecting against them is prohibitively expensive and/or technically difficult.