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.
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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.
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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.
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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
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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..
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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. |
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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.
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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. |
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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. |
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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
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Brad
Butman (Oceanography,
Sea floor mapping)
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Bill Schwab (Geology, Sea floor mapping)
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Marilyn ten Brink (Geochemistry)
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Robert Thieler (Coastal geology)
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Bill Danforth (Sea Floor Mapping)
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Jane Denny (Geology, Sea floor mapping)
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Ellen Mecray (Geochemistry)
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External Collaborators
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