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248
HARBOUR ENGINEERING.
works, in coiijunctioii with dredging, where necessary, have provided a
navigable depth, at the ordinary low stage of the river, of 10 feet from the
Dutch frontier up to Cologne, and 8| feet between Cologne and Caub at the
base of the steep slope below Bingen; above which point the available depth
at average low water is reduced to 6| feet, which is maintained up to
Philippsburg about 22j miles above Mannheim.
The Port of New York.—There are two navigable entrances (fig. 8) to
the port of New York. One, which is frequented by transatlantic liners and
ocean-going vessels generally, is flanked by Sandy Hook on the south and by
Coney Island on the north, and opens directly on to the Atlantic Ocean; the
other is an arm of the sea hemmed in between Long Island and the mainland,
known as Long Island Sound as far as its juuction with East River at Hell
Gate, and forming the principal route for coasting vessels trading to and from
the northern states and the Canadian provinces.
These entrances present features of direct and striking contrast, both in
regard to their nature and the means adopted for their amelioration. The
main entrance is broad and spacious, and, fronting the Atlantic, is exposed to
all its storms. Moreover, it is beset with shoals and sandbanks. Sandy Hook
itself is but a low-lying bank, more or less submerged, and varying from time
to time in form and extent.
Obviously, for such a regime, the process of suction dredging forms the
proper system of treatment, and this has been carried on for a number of
years past with eminently satisfactory results. There is at present a
minimum navigable depth of 30 feet at low water along the main ship channel,
and operations are well advanced towards the attainment of a depth of 40 feet
along a new and shorter route known as the Ambrose Channel.1
The tidal current is moderate. At the crest of the bar it rarely exceeds
li knots, and within the limits of the inner channels its maximum rate is
from 2 to 2J knots.
The Long Island entrance is characterised by a sinuous course, under-
going frequent and abrupt changes of direction. It is comparatively sheltered,
but has to wind its way amid the intricacies of an archipelago of inlets and
rocky reefs, some of the latter rising above the water level, but many of them
totally submerged and fraught with danger to navigation. The currents,
moreover, are rapid, reaching at certain points a speed of 10 knots, and eddies
are numerous. The impetus thus generated, combined with the irregularities
of the course, have been, in times past, the cause of numerous disasters to
shipping, particularly in the neighbourhood of Hell Gate, where the stream
is deflected at right augles past Hallet’s Point, to be split up into a multitude
of rivulets amid the hidden reefs which abounded at that point. By means
of blasting operations, however, on an extensive, not to say gigantic scale the
worst of these obstructions have been removed, and the channel is now
navigable in comparative ease, and, at anyrate, with safety.
1 A ruling depth in the Ambrose Channel of 35 feet at lowest ebb tide, throughout a
width of 1000 feet, was reported to have been realised in August 1907.