| The East Passage is favored by all deep draft vessels, but the West
Passage can be used by shipping drawing 20 feet or so. The Sakonnet River,
incidentally, isn't a river at all but an arm providing direct access to
Mount Hope Bay, an integral extension of the Bay. All three receive heavy
usage from myriads of pleasure boats, sport fishermen, and commercial fishing
vessels
If one were to draw a line from Whale
Rock off the Narragansett shore to the tip of Beavertail on Conanicut
Island, then to Brenton Point at Newport, and finally to Sakonnet Point
in Little Compton, Narragansett Bay would comprise the tidal waters to
the north of the line. This line across the three entrances is a distance
of 10.8 nautical miles. Northward of the line there are 94.5 square miles
of salt water. It's a run of 23.6 miles from Brenton Point up the East
Passage to the state pier on the Providence waterfront. The tankers that
enter the Bay pick up their pilots about 1.4 miles south of the line. in
Rhode Island Sound near the Brenton Reef
tight tower
Some students of Bay geography give
Narragansett Bay a substantially larger dimension, placing its southernmost
boundary along a line from Point Judith to Sakonnet Point, but most Rhode
Islanders feel they are in Rhode Island Sound and the open ocean once they
leave any of the three passages. Although the Rhode Island coastline trends
east to west, the Bay is aligned almost exactly along a north-south axis.
Within the Bay are three large islands:
Aquidneck, the largest, supports
Newport, a place of unusual charm and great historical significance; Conanicut
Island, which separates the West and East Passages; and Prudence,
approximately in the center. There are more than a dozen smaller islands,
and many rocky outcroppings. Although deep draft vessels can run aground
if they stray, relatively few obstructions affect small boat traffic. Boatmen
commit to memory perhaps a dozen rocky or shoal areas and sail about their
Bay with little concern for sudden scrapings groundings.
Shoreline topography is varied, in
some regions sloping rather steeply to the water's edge but over relatively
short distances, and in others lifting gradually only 15 or 20 feet above
the high tide line. Rocky headlands and boulder-covered shores are found
along the lower Bay near the entrances, while sand and gravel bluffs are
more common inland.
Salt marshes of importance to fish
propagation and water fowl have formed along the Sakonnet River, on sections
of the Conanicut and Prudence shores, and up the tributaries, and here
are salt marshes behind barrier beaches outside the Bay proper.
Most of the bedrock shoreline consists
of conglomerate sandstone and black shales deposited over 280 million years
ago. These rocks include coal deposits in Portsmouth and Bristol and graphite
in Cranston. Examples of earlier igneous and metamorphic rocks such as
granites and schists crop out along the shores of the southern section
and throughout the Bay's 1,850-square-mile drainage basin. Particularly
good examples can be seen along the Newport Cliff Walk.
The real molder of the Bay as it is
today was the ice of the Pleistocene Epoch, starting perhaps two million
years back and extending to only 15,000 years ago. Narragansett Bay was
an old sedimentary basin that had undergone intense stream erosion when
the ice came, grinding and crushing all but the hardest of the ancient
rocks, and picking up sand, gravel, and boulders. As a glacier paused in
its retreat, it dropped off deposits of these materials, creating thick
ridges which geologists call moraines. Boulders, called erratics, were
carried from as far away as Canada to puzzle latter-day investigators as
to their origin. As the glaciers melted northward, rivers deposited sand
and gravel to form broad plains and deltas. Good examples may be found
from Greenwich Bay to Providence. When the glaciers pulled back, the level
of the ocean rose and filled the Bay.
The deep gorge of the East Passage
was formed by glacial action. A new channel was formed by the ice for the
Pawtuxet River, which once, it is believed, emptied into Apponaug Cove
and Greenwich Bay, and now provides a boundary line for Warwick and Cranston.
Massive chunks of ice lingered behind
the retreating glacier, melting slowly, and formed some of the freshwater
ponds along Rhode Island's southern shores and at inland places near the
present Bay.
The Rhode Island shoreline is now
undergoing a slow but steady process of erosion under the carving of the
ocean storms and is submerging because of the slow rise in the level of
the sea relative to the land. This rise, as measured by the Newport tide
gauge, is about 1 foot/100 years.
Water depths in Narragansett Bay are
for the most part not great, and the bottom tapers gradually from Rhode
Island Sound to the head of the Bay. Average depths are about 24.5 feet
at mean low water in both the West Passage and the Sakonnet River, although
there is one 85-foot spot in the passage near Dutch Island. In the East
Passage, however, near the Castle Hill light, the depth is 188 feet and
depths of 100 feet are found all the way north to a point about halfway
along the Prudence Island shore.
A few Rhode Islanders have actually
seen what the bottom of their Bay looks like. After the 1954 hurricane,
the Army Corps of Engineers constructed an accurate replica in a large
prefabricated building at its test facility in Vicksburg, Mississippi,
as an aid to designing hurricane barriers. It was possible to walk from
island to island over narrow catwalks, look down into the glacial trough
of the East Passage and the man-made ship channel cut across the upper
Bay and on up the Providence River. Later the engineers added water to
simulate the tides, using a hydraulically controlled thruster to force
the water through the model. Ingenious methods were employed that enabled
the study of the movement of the water; bits of styrofoam were floated
and photographs taken of the distribution patterns that resulted.
The Army's engineers did not convince
Rhode Islanders that erection of hurricane barriers to protect the Bay
was desirable, and the expensive model lay in idleness in its shed for
a number of years. Some residents of the state thought it should be moved
from Vicksburg to Rhode Island and reassembled as a research tool and tourist
attraction, but their plan was proposed too late. The engineers had already
torn it down and gone on to other projects. |
