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


Results: Present Dredged Material Disposal Site

   Overview  |  Historical Disposal Sites  |  Dredged Material Disposal Site  |  Evidence for Dumping  |  Striping of Data  |  Outcropping Beds of Coastal Plain Strata  |  Sand Waves  |  Hudson Shelf Valley   
Click on figures for larger images.
Figure 5. Map showing shaded-relief bathymetry (contoured at 2m intervals) for the northern portion of the survey area.


 Figure 6. Map showing backscatter intensity, bathymetry contoured at 10 m intervals, locations of sediment samples, and surficial sediment texture (as pie diagrams).
 Figure 7. Shaded-relief bathymetric map with 2 m contours (left) and backscatter intensity (right) with the same 2 m bathymetric contours at a scale of 1:12.500 for the region surrounding the Dredged Material Disposal Site.

Figure 7
The present Dredged Material Dump Site (DMDS) (see Fig. 5,6 and 7) is marked by several mounds of material that extend to within 16 m of the surface; the shallowest mound (at 40° 22.7' N and 73° 51' W) is about 12 m from the sea surface. Elongate paired features, on the order of 50 to 75 m long and 40 m wide, are scattered throughout the site (see Fig.7). Their relief typically is about 1 m and some of the features are separated by depressions about 1 m deep. It is hypothesized that these are signatures of individual dumps of material from barges. Linear features on the order of 100 m long and aligned northwest-southeast, are observed on the saddle (40° 23.25' N and 73° 51.4' W) between the southern disposal mound and the present disposal site at water depths between 16 and 18 m. These linear features have about 0.5 m of relief. A few features with similar characteristics are observed to the north of the southern disposal mound (see Fig. 5). The origin of these features is unknown.

An area of uniformly smooth topography and low backscatter extends to the northeast, east, and southeast of the DMDS for about 1-2 km (see region between 40° 23' and 40° 24' N and 70° 50' W (Fig. 5, 6, and 7). The absence of the backscatter and bathymetric signatures of individual dumps in this area which are ubiquitous throughout much of the adjacent area, suggests that this area may be composed of fine material winnowed from the disposed dredged material and transported eastward and downslope toward the head of the Hudson Shelf Valley. The composition of the two surface sediment samples (stations 38 and 48, Table 1) obtained in this region, which are both clayey silt, support, but does not prove this hypothesis. Another region of relatively smooth topography and low backscatter (between 40° 22'N and 45° 23' N and centered at 73° 52' W) is found to the west of the DMDS. A circular region south of the DMDS (centered at 40° 22' N and 73° 51' W) is approximately 1 km in diameter and is characterized by relatively low backscatter intensity. Within the circular region, there are at least 10 individual mounds less than 2 m in height. This feature represents the site where sediments contaminated with dioxin were disposed and capped with sand in the late 1980's.
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Based on Butman, B., Danforth, W.W., Schwab, W.C., and Buchholtz ten Brink, M.B., 1998, Multibeam Bathymetric and Backscatter Maps of the Upper Hudson Shelf Valley and Adjacent Shelf, Offshore of New York: U.S. Geological Survey Open-File Report 98-616.
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Web page by: Donna Newman
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