HOW UNIQUE WAS HURRICANE SANDY? A COMPARISON OF THE INUNDATION DEPOSITS AND SURGE HEIGHTS FROM HURRICANE SANDY AND THE 1821 HURRICANE

On October 29, 2012 Hurricane Sandy inundated New York City, NY, raising water levels to 3.5 m above mean sea level at the Battery (located at the south end of lower Manhattan). Historical records indicate that this is the highest measured water level since records began at this location in the mid-1700s and simulated hurricane climatology ranks this storm as a 1-in-1000 year event. However, a newspaper article written in 1821 cites a water level rise of 13’4” (~4 m) above low water in one hour produced by a hurricane that year. Independent methods are needed to more accurately assess the storm surge height of this older historic storm.

Sediment deposits created by storm-induced coastal inundation serve as valuable proxies of storm activity. Sediment cores were taken from Seguine Pond, a ~1 m deep back-barrier pond located on Staten Island’s southern coast, about one month after Hurricane Sandy impacted the area. The age constraint on the 1821 deposit is developed by using carbon-14, cesium-137, and lead-210 radiometric dating techniques. The grain size distribution is measured for the Hurricane Sandy and 1821 event-deposits to help constrain flow conditions required for erosion and transport of sediment. The maximum grain size of both deposits is used to estimate their storm surge heights using an advective-settling model. Additionally, the reported water level rise of the 1821 surge is used in the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model to constrain the characteristics of the hurricane (i.e. storm track, forward speed, radius of maximum winds (RMW), and pressure difference between the hurricane’s eye and the ambient atmosphere (ΔP)).

We find that 1) the maximum grain size of the 1821 inundation deposit is larger than that of Hurricane Sandy’s deposit, suggesting that it was produced by a larger storm surge, 2) SLOSH modeling results indicate that a category 3 storm with a forward speed of 35 knots (~65 km/h), RMW of 25 miles (~40 km), and ΔP of 65 mb could produce the reported water level rise of the 1821 storm, and 3) sea-level rise and tides are two of the primary causes of Sandy’s very high water levels relative to the 1821 hurricane.