Narragansett Bay: A Friend's Perspective 
The Living Bay

Topography and Geology

Rhode Island is truly an ocean state. Nearly one-tenth of its entire inland area is covered by salt water. No resident is more than 30 minutes away by car from the water's edge. Narragansett Bay extends fingers into the very heartland of Rhode Island and occupies such a central position that from the air a traveler is likely to feel that the state consists more of water than of land. 

The Bay is Rhode Island's most fascinating and dominant natural feature. Greenwich Bay, the Providence River, and Mount Hope Bay are major appendages, and it in-as numerous coves and inlets of rivers and streams. headlands and peninsulas which provide shelter and safe harbors for fleets of small boats. 
 
Narragansett Bay has three entrances: from west to east, the West Passage, the East Passage, and the Sakonnet River. 

Satellite View of Bay 

Satelliteview. Massachusetts Bay is pictured at top right, Cape Cod (with Cape Cod Canal visible) at lower right, and Narragansett Bay at lower middle. From EROS Data Center, U.S. Geological Survey.

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. 

 

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