MEASURING STORM TIDE AND HIGH-WATER MARKS FROM HURRICANE SANDY IN NEW YORK

In response to the forecasted landfall of Hurricane Sandy, personnel from the U.S. Geological Survey (USGS) deployed storm-tide sensors along the eastern seaboard. The New York Water Science Center deployed 38 storm-tide sensors and 4 rapid-deployment gages (RDGs) in southeastern New York. Sensor locations were selected to supplement existing coastal gages and to collect data where models predicted significant storm-surge and storm-tide flooding. Storm surge is the rise in water levels above predicted astronomical tides; storm tide is the rise due to surge plus astronomical tide. Hurricane Sandy posed a particularly dangerous threat as the storm was expected to transition into a large and powerful extra-tropical cyclone, and hit during a period of higher astronomical tides.

During the storm, real-time water levels were available from the USGS network of coastal gages and RDGs. The timing of storm-tide inundation was extremely important. For example, along the south shores of New York City and western Long Island, the peak storm surge of 8 to 9 ft coincided with the astronomical high tide, which resulted in record storm-tide inundation in these areas. In the Peconic Estuary and northern Nassau County, however, the maximum surge of 7 to 9 ft and nearly 12 ft, respectively, occurred near the time of normal low tide, which helped spare these communities from further coastal flooding.

Within 10 days of landfall, USGS scientists retrieved the storm-tide sensors and RDGs, and surveyed high-water marks (HWMs). The RDGs in Suffolk and Westchester Counties recorded peak storm-tide elevations of 5.2 and 10.2 ft (feet) above NAVD88 (North American Vertical Datum of 1988), respectively. The coastal gages recorded peak storm-tide elevations from a low of 6.4 ft NAVD88 in eastern Suffolk County to a high of 10.6 ft in Kings County. HWMs, such as debris or seed lines, were documented as verification of sensor data and as indicators of peak storm tide. For comparison, the water levels indicated by the storm-tide sensors and HWMs ranged from 6 to 8 ft NAVD88 in the Peconic Estuary, 8 to 12 ft in northern Nassau County, and 9 to 17 ft in New York City. Data collected by the USGS for Hurricane Sandy are displayed and archived on an online mapper (http://water.usgs.gov/floods/events/2012/sandy) and are summarized in USGS Open-File Report 2013–1043.