Woods Hole Coastal and Marine Science Center

U.S. Geological Survey Studies in the New York Bight

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Introduction

     The New York-New Jersey metropolitan area is the most populated region of the United States. New York city, with a population of about 8 million, is the largest city in the United States and the New York & New Jersey metropolitan area, with a population of about 20 million, is the second largest in the world. The harbor estuary and the area offshore of New York is used for waste disposal, transportation, recreation, and commercial and recreational fishing.

Image showing bathymetry of coastal ocean offshore of New York metropolitan region
Figure. Bathymetry of the coastal ocean offshore of the New York metropolitan region (bathymetry from National Oceanic and Atmospheric Administration Coastal Relief Model). Click here to view USGS data coverages and to enlarge image.

USGS Research

     Since 1992, the U.S. Geological Survey`s Coastal and Marine Geology Program has been conducting studies offshore of New York designed to map and characterize the sea floor, to understand the transport and fate of sediments and associated pollutants, to map the inner shelf and sand deposits along the southern shore of Long Island, and to understand the recent geologic history. A long-term goal of these geological studies is to develop predictive models and geologic information to guide research and sustainable use of the coastal ocean.



Line SeparatorImage showing population density of the eastern portion of U.S.

Population density of the eastern United States. New York, with a population of approximately 17 million, is the sixth largest city in the world and is the most populated coastal region of the United States. Fifty percent of the U.S. population lives within 50 miles of the coast; about 80% within 200 miles.







Example image showing  a magnified view of the sea floor
Line Separator

Major Results

Sea Floor Mapping

       New surveys provide a highly detailed view of the sea floor The new images, based on sidescan sonar and/or multibeam, are similar in detail to an aerial photograph and show changes in seabed features over a wide range of scales that are caused by past and present natural and anthropogenic processes. In the New York Bight Apex, eleven geologic regions have been identified based on geologic surveys using sidescan sonar, high resolution seismic reflecting profiling, and bottom sampling. These regions are a result of the geologic history of the region, natural processes and anthropogenic activity. The principal topographic feature of the region is the Hudson Shelf Valley, the drowned channel of the Hudson River that was formed at lower stands of sea level. It extends across the continental shelf from offshore of New York City towards the shelf break and is potentially both a site for accumulation of sediments as well as a conduit for transport of sediment (this is a PDF file - Download Adobe Acrobat Reader) and associated contaminants across the shelf. Along the southern shore of Long Island, sidescan sonar and high-resolution seismic reflection profiling show a blanket of modern sediment that is thinner in the east than in the west..

Example image showing  locations of sediment samples taken in the New York Bight

Fate of Pollutants

      The bottom sediments offshore of New York are contaminated. Contaminants are concentrated in the upper Hudson Shelf Valley, principally from disposal of sewage sludge since the 1950`s. Contaminants have dispersed as much as 100 km down valley.

Example image showing a sidescan-sonar profile

Sand Resources along the southern shore of Long Island, New York

      Long Island is the southern boundary of the last glacial advance in the eastern part of North America. The south shore of Long Island consists of reworked sediment deposited by the glaciers and includes shallow lagoons and a low-relief barrier island system. Detailed mapping of the geology along the southern shore of Long Island has been carried out to investigate the role that geology plays in the evolution of this coastal region, and to provide a regional framework to assess sand-resource availability for beach-nourishment projects. Detailed mapping of the sea floor along the inner-continental shelf shows that geology controls the evolution of this coastal system. Poorly lithified sedimentary rocks are overlain by a blanket of glacial and modern sediment typically less than 15 m thick. In some places such as offshore of Watch Hill, the Cretaceous strata crop out on the shelf. To the west (downdrift) of this outcrop, the modern sand is reworked into a series of shoreface-attached ridges up to 5 m thick. To the east (updrift) of this outcrop, the modern sediment thickness is typically less than 2 m thick. Because of the lack of a source of modern sand, the barrier islands east of Watch Hill have been more susceptible to inlet breaching than those to the west.

Example image showing an instrument that is used in field experiments

Circulation in the Hudson Shelf Valley

      A field experiment was conducted during the winter of 1999-2000 to investigate the transport of sediments and associated pollutants in the coastal waters offshore of the New York - New Jersey metropolitan region. The experiment was designed to observe sediment transport and circulation in the vicinity of the Hudson Shelf Valley, a 20-m deep valley that extends from the shelf edge across the continental shelf to water depths of about 20 m, terminating near several historical dumpsites. Geochemical evidence (for example, elevated lead concentrations) indicates that contaminated sediments have dispersed seaward along the axis of the Valley over the last 50 years.  The field observations show episodic down-canyon flow driven by storm winds from the northeast (downwelling). These winds also cause large surface waves that resuspend the bottom sediments, resulting in down-canyon transport of sediment during these events. Over the entire experiment however, the transport of sediments was dominated by up-valley currents driven by winds from the northwest. These currents were also sufficiently strong, 20-40 cm/s near the bottom, to resuspend the bottom sediments and resulted in net up-valley transport. Although the observations are only for the winter season, the up-valley transport has implications for the long-term dispersal of fine-grained sediment and associated contaminants in the New York Bight region.

Image of New York Bight region with vulnerability index

Coastal Vulnerability

     Relative vulnerability of the coast to sea-level rise has been quantified based upon geomorphology, shoreline erosion and accretion rates (m/yr), coastal slope (percent), rate of relative sea-level rise (mm/yr), mean tidal range (m),and mean wave height (m). The combination of these variables and the association of these variables to each other furnishes a broad overview of regions where physical changes will occur due to sea-level rise. The coastal vulnerability index (CVI) values range from moderate to very high in the New York Bight region. In the New York - New Jersey Region, the coastal vulnerability index (CVI) is primarily controlled by the coastal geomorphology. The open-ocean shoreline, for example, is composed primarily of high-risk sandy barrier islands, while risk due to geomorphology is lower for the lagoons and along the bluffs of eastern Long Island.

Example image showing a portion of the Historic Area Remediation Site

Historic Area Remediation Site (HARS)

      Disposal of dredged and other material offshore of the New York - New Jersey metropolitan area has resulted in extensive anthropogenic material on the sea floor. Part of the area has been designated as the Historic Area Remediation Site (HARS). The sea floor of the HARS, approximately 9 square nautical miles in area, is being remediated by placing a minimum one-meter cap of clean dredged material on top of the existing surface sediments that exhibit varying degrees of degradation from previous disposal activities. The regional geology and changes in the characteristics of the sea floor caused by remediation are observed in multibeam surveys carried out in 1996, 1998, and 2000 by the USGS in cooperation with the U.S. Army Corps of Engineers. Comparison of the topography and backscatter intensity from the three surveys shows changes in bathymetry and sediment properties resulting from placement of dredged material prior to closure of the Mud Dump Site, and remediation.



USGS Collaborators

  • Brad Butman (Oceanography, Sea floor mapping)

  • Bill Schwab (Geology, Sea floor mapping)

  • Marilyn ten Brink (Geochemistry)

  • Robert Thieler (Coastal geology)

  • Bill Danforth (Sea Floor Mapping)

  • Jane Denny (Geology, Sea floor mapping)

  • Ellen Mecray (Geochemistry)






External Collaborators



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