Ketchum
Bostwick H.
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The oceanography of the New York Bight
Ketchum
Bostwick H.
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The New York Bight consists of the waters lying between Cape May, New Jersey,
and Montauk Point, Long Island. A portion of the general southwesterly current known
as the Coastal Drift lies in the seaward part of the Bight. Inshore from the Coastal Drift
is an area of complex hydrography where the combined outflows of the Hudson River and
other rivers enter the sea.
In the region where the New Jersey and Long Island coastlines converge, an area 25
nautical miles on each side has been studied at all seasons of the year. This area extends
from Sandy Hook southward to a point off Seaside Heights, eastward to 73°15' W longitude,
north to the Long Island shore, and westward to Rockaway Inlet.
The depth of water in the area averages about 90 feet, except in the innermost part
of the Hudson Canyon which runs roughly northwest-southeast across most of the survey
area. In the Canyon, depths in excess of 240. feet are found within the limits of the area
studied.
The hydrographic conditions in the area are in essence similar to those off the mouths
of other large rivers. The combined flows of the Hudson and other rivers entering the
surveyed area discharge enough fresh water annually to replace about one-half of the total
volume of water under the 600 square miles of sea surface extensively surveyed. The salinity
within the area is nearly as high as that of adjacent coastal water, however, and the
actual quantity of river water within the area at any time rarely exceeds one percent of
the total volume of water. Quantitative evaluation of these factors has led to the conclusion
that there is an active circulation within the area which rapidly disperses the introduced
river effluent.
Many surveys of coastal and estuarine waters have been made. Outstanding among
these are the survey of the River Tees, (1931, 1935), of the Tamar Estuary, (Hartley and
Spooner, 1938; Milne, 1938), and of Alberni Inlet, (Tully, 1949). The general principles
of estuarine circulations may be summarized as follows: In order to remove the
added river water there must be a non-tidal drift of mixed water in a net seaward direction.
When river flow remains constant, a steady state distribution of fresh and salt water
throughout the estuary is attained, and at such times the net transport of river water seaward
through any complete cross section of the estuary exactly equals the contribution of
fresh water from the river during the same interval of time. As the mixture containing
the river water moves seaward it gets progressively more saline, as additional sea water is
entrained. In order to provide this sea water there must be a counter drift having a net
flow in a landward direction.
Superimposed on these necessary parts of the circulation are tidal and wind currents.
The velocities of the tidal currents are commonly much greater than the velocity of the
non-tidal drift, making the latter difficult to measure directly. It can be inferred, however,
from the distribution of river water, as derived from the salinity distribution. Using the
river water in this way we have evaluated the exchanges of the waters within the New
York Bight. Tully (1949) has analyzed the circulation in Alberni Inlet by similar
methods. Tidal current measurements made by the Coast and Geodetic Survey at various locations
in the northwestern corner of the surveyed area are summarized by Marmer
(1935). At Scotland Lightship, which is the location of the stations at the western end
of Section A in Figure 1, the total excursion which results from the flood or ebb tidal currents
is less than two miles. The currents at Ambrose Lightship, about five miles to the
eastward, produce displacements only about half as great. The tidal displacements throughout
the rest of the area are presumed to be less than these. The pattern of distribution of
properties will be displaced, therefore, a distance less than ±1 mile at various stages of the
tide. This distance is small in comparison to the size of the area surveyed, especially when
considering the fact that distances between stations ranged from 5 to 8 miles. It was unnecessary,
therefore, to attempt to take comparable stations at similar stages of the tide.
Other considerations, beside its interesting hydrography, have contributed to the choice
of this area for study. Because it is adjacent to centers of dense population and heavy industrial
concentration, the New York Bight serves the conflicting purposes of waste disposal
and recreation.
Sewer effluents and industrial wastes enter the area by way of the rivers. Sewage
sludges are barged out and dumped within the region studied. During the period covered
by our surveys, The National Lead Company commenced operations to barge and discharge
at sea the waste from its titanium plant at Sayreville, New Jersey. Since iron was a major
constituent of this waste, analyses for iron in the water were made at each station, and the
results have been valuable in checking the rate of the circulation which was computed from
the distribution of river effluent.
The New York Bight is also used extensively for recreational purposes. Because the
area is readily and cheaply accessible by public transportation it must serve the recreational
demands of a large part of the population of metropolitan New York. Sport fishing, bathing
and boating are the principal recreational activities. Small but valuable commercial
fisheries for shellfish and fin-fish also exist.
The purpose of this study was to investigate the hydrographic processes in the New
York Bight since they have an important bearing on the general problems of coastal oceanography
and a knowledge of them should lead to a more successful evaluation and utilization
of the area for the diverse purposes it must serve.