The Impact of Tidal Phase on Hurricane Sandy's Flooding Around New York City and Long Island Sound

Abstract

How do the local impacts of Hurricane Sandy's devastating storm surge differ because of the phase of the normal astronomical tide, given the spatiotemporal variability of tides around New York? In the weeks and months after Hurricane Sandy's peak surge came ashore at the time of local high tide at the southern tip of Manhattan and caused record-setting flooding along the New York and New Jersey coastline, this was one question that government officials and critical infrastructure managers were asking. For example, a simple superposition of the observed peak storm surge during Sandy on top of high tide in Western Long Island Sound comes within 29 cm (less than a foot) of the top elevation of the Stamford Hurricane barrier system which would have been overtopped by 60 cm surface waves riding over that storm tide. Here, a hydrodynamic model study of how shifts in storm surge timing could have influenced flood heights is presented. Multiple flood scenarios were evaluated with Stevens Institute of Technology's New York Harbor Observing and Prediction System model (NYHOPS) having Hurricane Sandy arriving any hour within the previous or next tidal cycle (any hour within a 26-hour period around Sandy's actual landfall). The simulated scenarios of Sandy coming between 7 and 10 hours earlier than it did were found to produce the worst coastal flooding in the Upper East River, Western and Central Long Island Sound among the evaluated cases. Flooding would have generally been worse compared to the real Sandy in Connecticut and the areas of New York City around the Upper East River between the boroughs of Queens and the Bronx, exceeding record flood heights. However, the New York Harbor region would still have seen its record flood elevation exceeded, so the storm's impact could have been more widespread. The hydrodynamic model results suggest that the still-water levels would have risen to within 75 cm of the top elevation of the Stamford storm surge barrier, 46 cm lower than the naïve superposition of astronomical tide and storm surge.