Hurricane Sandy Disrupts USGS Study of the Barnegat Bay-Little Egg Harbor Estuary in New Jersey, Provides Additional Research Opportunities
On October 29, 2012, Hurricane Sandy made landfall just south of Atlantic City, New Jersey, with wind speeds ranging from 50 to 64 knots (about 60 to 75 miles per hour). The storm had significant impacts on Barnegat Bay-Little Egg Harbor estuary, where the U.S. Geological Survey (USGS) and the New Jersey Department of Environmental Protection (DEP) are conducting a multiyear, multidisciplinary study (see Mapping, Measuring, and Modeling to Understand Water-Quality Dynamics in Barnegat Bay-Little Egg Harbor Estuary, New Jersey, this issue.
The arrival of Hurricane Sandy during the Barnegat Bay-Little Egg Harbor estuary study will allow scientists to investigate not only how various factors—shape of the shoreline and seafloor, patterns of water circulation, distribution of sediment—influence the estuary's water quality, but also how those factors respond to significant storm events. Multidisciplinary mapping and data collection conducted by USGS scientists before the storm, and a network of water-level and water-quality sensors throughout the study area (some deployed in anticipation of the hurricane's arrival), will provide a foundation for rigorous post-storm impact assessments.
During Hurricane Sandy, storm surge within Barnegat Bay raised water levels 2 meters (6 feet) above normal high-tide levels, flooding estuarine coastlines and damaging coastal infrastructure. Barrier-islands that form the estuary's eastern boundary were eroded and breached. Two of these breaches—near Mantoloking, New Jersey—are shown below in aerial photographs taken by the National Oceanic and Atmospheric Administration (NOAA). Airborne lidar (light detection and ranging) surveys flown before and after Sandy by the USGS Coastal and Marine Geology Program's lidar project also documented the breaches, and showed decreases in barrier-island beach and dune elevations of as much as 6 meters (20 feet). Such information is essential for focusing the response effort in the most heavily impacted areas and for identifying potential sediment resources for coastal-restoration projects.
As part of the Barnegat Bay-Little Egg Harbor estuary study, USGS scientists conducted seafloor mapping and related data collection in November 2011 and March 2012. A third seafloor survey had been scheduled for late November and early December of 2012 but had to be postponed because of Sandy's impact on the estuary, which was littered with storm debris—including houses, docks, and cars—that was still being cleaned up as of late January 2013. Rescheduled for March 2013, the post-storm mapping and data collection will enable an assessment of how the shape of the estuary floor and the characteristics of its sediment changed as a result of the storm (and the ensuing cleanup efforts), and how those changes might affect estuarine habitats. Model simulations of conditions during Sandy will focus the post-storm survey on areas most likely to have experienced dramatic changes. The instruments used for the March survey will also be helpful for identifying the location of submerged debris, which will facilitate continued post-storm clean up.
Because the Barnegat Bay-Little Egg Harbor estuary project includes modeling to predict how the water and sediment move in response to tides, storm currents, and other influences, a hydrodynamic model had already been constructed for the study area. This model proved extremely useful after Hurricane Sandy, helping scientists to assess the effects of barrier-island breaches on water quality and tidal water levels within the estuary. The residence time of estuarine water—the time needed to completely flush the estuary—is commonly used as an indicator of water quality. In general, the shorter the residence time, the better the water quality. To determine how the large breach near Mantoloking would affect the residence time of the water in the Barnegat Bay-Little Egg Harbor estuary, pre-breach and post-breach scenarios were simulated with the hydrodynamic model. Comparing the results of the model simulations showed a decrease in residence time of 10 days for the simulation that included the large breach. This finding indicates that there is potential for improved water quality in the estuary if the breach were to remain open. The simulation also indicates little to no increase in tidal water levels on the mainland shore as a result of the breach. Such information is critical for coastal-resource managers, who look to science to guide post-storm coastal management.
The well-established water-level and water-quality monitoring network within the estuary collected critical data about conditions during the storm, despite the loss of a few sensors and related infrastructure. The network recorded maximum water levels around the bay during the storm, providing vital input data for hydrodynamic-model simulations. Of particular help was the water-quality monitoring station at Mantoloking, which remained operational throughout the storm even though the barrier island was breached adjacent to its location (on bridge piling west of area depicted in the lidar images above). The station recorded peak turbidity (sediment concentration in the water column) more than 40 times the normal range. Such data are invaluable to scientists trying to understand how barrier-island breaches alter the water quality of estuaries during and after storms. Observations of water levels and water quality from around the bay will continue to yield information for post-storm model simulations and for monitoring the impact of coastal-restoration projects.
The effects of tropical and extratropical storms on estuaries and coasts are multifaceted—they can change the shape of the coastline dramatically, thereby affecting coastal resources and ecosystems. A multidisciplinary approach, such as the study underway in Barnegat Bay-Little Egg Harbor estuary, is invaluable for providing data to quantify storm impacts and to guide future coastal restoration and rebuilding efforts.
(Read more about USGS responses to Hurricane Sandy at USGS Scientists Predict, Measure Sandy's Impacts on the Coastal Landscape, USGS Continues Response to Hurricane Sandy, and Start with Science to Address Vulnerable Coastal Communities .)
in this issue:
Hurricane Sandy Disrupts USGS Estuary Study, Provides Additional Research Opportunities