page_title: Narragansett Bay
section_title: Tidal patterns
hierarchical_section_title: Narragansett Bay / Oceanography / Tidal patterns
caption_attribution_description: English: Rose Island, located in the Narragansett Bay, in the U.S. state of Rhode Island. Photo taken May 30, 2005, by me. Originally incorrectly identified as Hope Island.
context_page_description: Narragansett Bay is a bay and estuary on the north side of Rhode Island Sound covering 147 mi², 120.5 mi² of which is in Rhode Island. The Bay forms New England's largest estuary, which functions as an expansive natural harbor and includes a small archipelago. Small parts of it extend into Massachusetts.
  There are more than 30 islands in the Bay; the three largest ones are Aquidneck Island, Conanicut Island, and Prudence Island. Bodies of water that are part of Narragansett Bay include the Sakonnet River, Mount Hope Bay, and the southern, tidal part of the Taunton River. The bay opens on Rhode Island Sound and the Atlantic Ocean; Block Island lies less than 20 miles southwest of its opening. Narragansett Bay can be seen on NOAA Chart 13221.
context_section_description: Tides in the watershed are measured at Providence, Fall River, Quonset Point, Conimicut Light, Prudence Island, and Newport. In shallow water, sound waves are used to measure water height by precisely measuring their travel time. In deeper water, tides are measured with pressure-sensing tide gauges that are placed on the ocean floor to measure water height. 
  The bay's tides are semi-diurnal, meaning that the region experiences two high and low tides daily. The tides range in height from 3.6 feet (1.1 m) at the bay's mouth and 4.6 feet (1.4 m) at its head. Water depth varies about 4 feet (1.2 m) between high and low tide. The lunar, semi-diurnal M2 tide occurs at a period of 12.42 hours, with two tides occurring in the watershed every 24 hours and 50 minutes. The watershed's neap and spring tides occur every 14.8 days. In Narragansett bay, the tides show a distinct double-peak flood during high tide and single peak ebb during low tide.
caption: Rose Island attributes its name to its rose shape at low tide.
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