LAUSR

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, extreme flood events. Staten Island, New York, suffered devastating damage from Hurricane Sandy, including 23 fatalities, of which 18 occurred in the neighborhoods along the island’s eastern shore. This study demonstrates that the elevated berm along the eastern shore may have contributed to the concentration of fatalities in the area by increasing the speed at which seawater rose, causing some people to be trapped in places where they could not escape rising waters. The study uses a hydrodynamic model to simulate Hurricane Sandy flood conditions, providing water depth, rise rate, and velocity. Statistical analyses show that water rise rate influences mortality, while other flood characteristics and several demographic and socioeconomic factors do not. A model experiment that qualitatively 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 increased probability of mortality by worsening the water rise rate during Sandy by about 50%. The potential increase in mortality needs to be taken into account when designing coastal protections. If a protection strategy does not prevent low-probability, extreme floods, then there is a trade-off between protection against more frequent floods and increased risk of mortality during extreme floods.