USING INUNDATION DEPOSITS TO CONSTRAIN THE STORM SURGE HEIGHTS OF STORMS THAT AFFECTED NEW YORK CITY, NY: HOW DOES HURRICANE SANDY COMPARE?
BRANDON, Christine M., Department of Geosciences, University of Massachusetts Amherst, 611 North Pleasant St, 233 Morrill Science Center, Amherst, MA 01003, WOODRUFF, Jonathan D., Department of Geosciences, University of Massachusetts Amherst, Amherst, MA 01003 and DONNELLY, J., Geology & Geophysics Department, Woods Hole Oceanographic Institution, MS #22, 360 Woods Hole Rd, Woods Hole, MA 02543, cbrandon@geo.umass.edu
The importance of extreme events in shaping ecosystems and governing sediment transport is in part determined by how often these events occur. By their very nature these events are rare, making it difficult to accurately assess their return frequency. 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, tide gauge data alone is generally too short to either obtain meaningful extreme value statistics, or evaluate the skill of flood probabilities derived solely from numerical simulations. Thus there is a real need for longer flood reconstructions of the New York City region. Further, questions remain with respect to whether extreme events like Sandy serve to mobilize contaminants (e.g. lead, mercury) within the harbor or cover these sediments with more pristine glacial material eroded from the surrounding landscape.
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 cores contain several coarse grained deposits most likely associated with storm surge inundation of the pond, including a surficial deposit associated with Hurricane Sandy’s surge. Age constraints on the inundation deposits are developed by using C-14, Cs-137, and Pb-210 radiometric dating methods. The grain size distribution is measured for the event deposits to help constrain flow conditions required for erosion and transport of sediment. The maximum grain size of the deposits is used to estimate their storm surge heights using an advective-settling model.
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) sea-level rise and tides are two of the primary causes of Sandy’s very high water levels relative to these older storms, and 3) inundation deposits show decreased concentrations of heavy metals than the background sediment, suggesting that storms can sequester contaminated sediments.
