APPENDIX B 

 HnRRICANE SURGES AND TIDAL HTDRADLICS 



NORHAL CONDITIONS IN NAHRAGANSETT BAT 



B-1. GENERAL 



Narragansett Bay reaches Inland about 26 Biles in a northerly 

 direction from the ocean to Providence, and has a water area, 

 including Mount Hope Bay and the Sakonnet River, of approxiinately 

 lUO square miles. The width of the bay across the mouths of the 

 East and West Passages is h miles, and across the mouth of the 

 Sakonnet River at Sachuest Point, slightly over 2,5 miles. The 

 widest stretch of the bay is Just south of Prudence Island idiere 

 there is close to 6 miles of open water. Depths range frcm 50 

 feet in the lower West Passage, l60 feet in the East Passage, 

 and $0 feet at the mouth of the Sakonnet River to shallow and 

 shoal water in the innumerable anall inlets and indentations in 

 the Upper Bay. South of Narragansett Bay is Rhode Island Sound 

 and the Atlantic Ocean, with Block Island and Long Island to the 

 west and Buzzards Bay and the Elizabeth Islands to the east* 

 Approximately 90 miles outside the bay lies the edge of the Con- 

 tinental Shelf where the water drops in depth from 600 feet to 

 3,000 feet in about 12 miles. 



B-2. ASTRONCMICAL TIDES 



Two high and two low tides occur each lunar day in Narragansett 

 Bay, with the time between high and low tide varying frott h hours 

 and Ul minutes to 7 hours and U7 minutes and averaging about 6 

 hours and 12 minutes. The greatest variations exist with the oc- 

 currence of spring tides, which prevail with the full and new 

 moons. The mean tidal range, between mean low and mean high water, 

 is 3.5 feet at Newport, U,6 feet at Providence and U.U feet at 

 Fall River. The time lag of the mean high tide between Newport 

 and Providence is about 10 minutes. Tidal data for these two 

 locations aire summarized in Table B-1, 



B-3, FACTORS INFLUENCING GRAVITATIONAL TIDES 



The predicted tides in Narragansett Bay are subject to numerous 

 meteorological influences such as changes in atmospheric pressure 

 and strong winds, besides the normal gravitational effects of the 



B-1 



