Hurricane Sandy was an extreme storm with a historic impact on the northeastern U.S. The proposed work will lead to a better understanding of this event by placing it in the context of the regional paleohurricane record. To compare Hurricane Sandy with past storm events, the project will conduct numerical surge and wave modeling, as well as textural analyses of Sandy-related and paleo-overwash deposits. This work will leverage previous surge modeling and paleo-overwash studies by the PIs in order to develop a more comprehensive paleohurricane record for the New York/New Jersey/Connecticut area. In addition, the project will compare Hurricane Sandy with modeled synthetic storm scenarios to evaluate the likelihood of Sandy-like events under current and future climate conditions.
This research will help to determine the frequency and probability of severe storms in a heavily populated coastal region of the U.S. Two undergraduate students and two post-doctoral researchers will be involved. The PIs will continue ongoing engagement with managers and policy makers.
Hurricane Sandy was the worst storm in memory for many places on the northeastern seaboard, causing tremendous damage, disruption, and a large number of fatalities. In New York City (NYC), Sandy caused the highest surge flooding of the instrumental record (~2.75 m above mean high water at the Battery). In New Jersey and Long Island, NY, large portions of the coastline were inundated and barrier islands were overwashed with large washover fans deposited in backbarrier environments. These overwash deposits provide a measure of Sandy’s impact to the region. When compared to other historic and prehistoric archives of overwash deposition, these deposits will provide an assessment of the frequency and climatological significance of Hurricane Sandy like events. In this project, we conducted field surveys at fourteen backbarrier salt marsh sites following Sandy to ascertain the scale and character of the overwash deposit evidence of Sandy’s passage. Sandy’s deposit evidences were then compared with the deposits induced by other significant historical storms in the region. To facilitate the interpretation of these deposit evidences, we also carried out a series of numerical modeling of the storm surge and wave included by Sandy and other significant storms in the region. Of the fifteen sites surveyed, only two contained significant overwash fan deposition, on Long Beach, NJ, very close to Sandy’s landfall point, and Seguine Pond on Staten Island. Cores from these sites provide evidence of numerous earlier historic and prehistoric overwash events. Especially, all fifteen sites contain a large overwash fan that dates to the early 19th century, likely the result of the infamous 1821 hurricane. At Seguine Pond the event bed related to Sandy was thicker than the one from 1821, but the 1821 event bed was significantly coarser than the Sandy layer. The thinner and coarser 1821 layer, relative to the Hurricane Sandy deposit, suggests the 1821 hurricane was a more intense, but sorter lived event. Inverse modeling of wave heights based on the size of the sediment transport and hindcast surge modeling confirm that the 1821 hurricane was a fast moving (moving northward at 40 mph; more than twice the speed of Sandy) and had maximum sustained winds of between 115 and 130 mph (a category 3 storm on the Saffir-Simpson Scale). We initially suspected that although Sandy generated higher water level than the 1821 hurricane, it might have induced much lower waves and thus was less capable to transport sediments. Our numerical modeling, however, shows that that wave heights of Sandy and the 1821 storm are similar for most sites. Although not supported by the numerical simulations, we cannot yet confidently rule out the influence of the wave height, because of the uncertainty in the numerical simulation for the early storms, like the 1821 storm, due to the lack of accurate input, especially the storm size. The coarser event bed associated with the 1821 hurricane, relative to Hurricane Sandy, may be related to higher velocities of surge related currents (more water was moved onshore more quickly in 1821 relative to Sandy). These comparisons thus motivate us to perform systematic uncertainty analysis for all early storms, in comparison with all evidence in the spatially distributed marsh sites. In addition to wave height, we will also check the velocities of the onshore current associate with these storms. The project combines geological evidence and numerical simulations to better understand hurricane climatology, bridging the fields of paleohurricane research and hydrodynamic modeling and risk analysis. Given the large uncertainties in both the instrumental and sedimentary records for early storms, it is necessary to compare and combine all information to better understand the hurricane historical and prehistory, so that we will be able to estimate future risk more accurately. The project also has broad educational and societal impact. Three undergraduate guest students, one graduate student guest student and one WHOI postdoc assisted in field surveys, gaining valuable training in field survey techniques. One postdoc at Princeton carried out a large number of storm analysis and storm surge numerical simulations, gaining experience in data analysis and numerical modeling to continue her research on hurricane and storm surge analysis. One journal paper is in press in Scientific Reports and another one is in preparation. Results of the project have also been presented at scientific conferences as well as at meetings for the general public.
