SEDIMENTARY RECONSTRUCTIONS OF FLOODING AND SHORELINE CHANGE OF STATEN ISLAND, NY: IMPLICATIONS FOR FUTURE MANAGEMENT OF NEW YORK HARBOR

Extreme events such as hurricanes and severe winter storms play an important role in shaping coastal environments in the northeast U.S.; however, their rarity makes assessing their geomorphic impact difficult. One such event occurred on October 29, 2012 when Hurricane Sandy inundated New York City, raising water levels to 3.5 m above mean sea level at the Battery (located at the southern end of Lower Manhattan). Historical records indicate that this is the highest measured water level since observational records began at this location in the mid-1700s. However, tide gauge data alone is generally too short (<100 years) to obtain meaningful extreme value statistics. Thus, evaluating the long-term impact of severe storms in the New York City region requires a longer record of flood reconstructions.

This research utilizes two techniques to extend the flood record: sedimentological analysis of cores from coastal back-barrier ponds and historical analysis of coastal maps. Cores were taken from three back-barrier ponds located on Staten Island’s southern coast about one month after Hurricane Sandy impacted the area. They contain several coarse grained deposits that are likely associated with storm surge inundation of the ponds, including a surficial deposit associated with Hurricane Sandy’s surge. The grain size distribution of the deposits is measured to help constrain flow conditions required for the erosion and transport of sediment. Age constraints on the inundation deposits are developed by using C-14, Cs-137, and Pb-210 radiometric dating methods. Additionally, the timing of events can be constrained by changes seen in historical maps, such as the opening and closing of inlets to the ponds. Maps can also be used to identify land use changes that may be related to changes in the background sedimentation in coastal ponds.

Here, we present a multi-centennial sedimentary record of storm surge inundation and land use change for lower New York Harbor. We find that 1) several deposits have a maximum grain size larger than Hurricane Sandy’s deposit, suggesting that they were created by larger storm surges, 2) storms can alter the coastline by opening and closing inlets to ponds, and 3) land use alterations can appear in the sedimentary record as changes in the background sedimentation.