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Multibeam Bathymetric and Backscatter Maps of the Upper Hudson Shelf Valley and Adjacent Shelf, Offshore of New York

Bradford Butman, William W. Danforth, William C. Schwab, and Marilyn Buchholtz ten Brink

Based on USGS Open File Report 98-616

Figure 1. Map showing location of multibeam survey (yellow outline)
Figure 1. Click for larger image (800 X 509 pixels, 53 Kb)

Map showing location of multibeam survey (yellow outline). The multibeam survey is nested within a sidescan sonar and high-resolution geophysical survey of a larger area (see Schwab and others, 1997a, 1997b) carried out as part of a USGS program to map the surficial geology and shallow subsurface structure offshore of major metropolitan centers. Light tones are high backscatter material (outcropping rock, boulders, gravel and coarse sand), low backscatter material (fine sand, silts and clay) is dark tones. Contours in meters.
The objective of the U.S. Geological Survey mapping project is to map the surficial geology and subsurface stratigraphy of the Hudson Shelf Valley and adjacent shelf from its head in the Christiansen Basin at about 40° 25' N and 73° 48' W to where it crosses the outer shelf at about 39° 40' N and 72° 50' W (Fig. 1). The northwesterly area of the survey encompasses a region of the shelf that may provide sediment to the valley as well as the principal disposal sites used since the 1800's. The offshore easterly limit of the survey area is 73° W.
The Hudson Shelf Valley (HSV) is 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 (Fig. 1). The valley is the principal topographic feature of the middle Atlantic Bight and is potentially both a site for accumulation of sediments as well as a conduit for transport of sediment across the shelf. In November 1996, the U.S. Geological Survey (USGS) conducted a multibeam echosounder survey of the upper HSV and adjacent shelf (Fig. 1). This multibeam survey is nested within a sidescan-sonar and high-resolution geophysical survey of a larger area (see Schwab and others, 1997a, 1997b). The surveys were conducted as part of a USGS effort to map the continental margin offshore of major metropolitan centers (Gardner and others, 1998) to provide a regional geologic framework to address environmental, resource and hazard issues, and as a basis for sustainable management of the coastal ocean.

The detailed maps of the geologic framework and sedimentary environments offshore of New York that have resulted from these surveys have guided sampling and process studies carried out as part of a USGS study of the transport and long-term fate of sediments and contaminants in this region (Buchholtz ten Brink and others, 1998). This progress report presents maps of topography, acoustic backscatter (a measure of seabed roughness and hardness), and preliminary interpretations of the sea floor features. An additional multibeam survey to complete coverage in the HSVis planned for the fall of 1998. The survey area contains the Dredged Material Disposal Site used for disposal of material from the New York - New Jersey harbor region. The area was closed to dumping of contaminated sediments in 1997, and was designated as the Historic Area Remediation Site, where disposal of clean material will cover existing sediments. Two other disposal sites in the region, one for sewage sludge (the"12 mile site") and one for cellar dirt, were discontinued in 1987 and 1994 respectively.

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This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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