per year since 1930 (see report by the Coiancil on Wave Research in 

 Proceedings of the First and Second Conferences on Coastal Engi- 

 neering, 1952). If this trend continues and storms of the magnitude 

 of the 1938 and 195U hurricanes were to occur at the end of the next 

 50 years, flood levels would be approximately one foot higher than 

 were actually experienced in these storms. The effect of rising 

 sea level is to increase the severity of future hurricane tidal 

 flooding, 



36. STORM TRA.CKS 



Bach of the three great recent hurricanes namely those of 1938, 

 19hh and 195ii followed a path from 20 to 80 miles west of Narragansett 

 Bay, thereby placing the bay in the sector of the strongest and most 

 damagixig hurricane winds and in the sector where the storm surge is 

 highest. Figures 2 and 3 show these stem tracks, 



37. SELECTION OF DESIGN HURRICANE TIDAL FLOOD 



In the design of protective works, structures must be built of 

 sufficient height and strength to withstand the most severe conibi- 

 nation of storm tide and wave action that can reasonably be expected, 

 A "design hurricane" for use in determining the required height of 

 protective structures has been established through the joint co- 

 operation of the U, S, Weather Bureau and the Beach Erosion Board, 

 assisted by the Texas A & M Research Foundation, T he ba sis of the 

 design storm is a transposition of the 19hh hurricane because this 

 storm when it was off Cape Hatteras, had the greatest amovmt of 

 energy of any recorded stoiro along the Atlantic Coast, However, 

 the 19hh hurricane when it struck New England was not nearly so 

 seriotis as either the 1938 or 195U hurricanes because (l) its energy 

 had been partly dissipated over the land north of Cape Hatteras, and 

 (2) it struck at a time of low tide. In deriving the design hurri- 

 cane, the 19lili storm was transposed so that it woiild be over water 

 between Cape Hatteras and the New England coast, resulting in less 

 drop in barometric presstire at the center of the storm than actually 

 occvirred in 19Ui, The transposed hurricane, having the intensity 

 of the 19hh hTirricane off Cape Hatteras, was assumed to ipove with a 

 forward speed of kO knots (about U6 miles per hour) in a northerly 

 direction and to pass over New England with its center li9 nautical 

 miles west of Providence, This would place Narragansett Bay in the 

 most critical area of the storm. Wind velocities were ascertained 

 by the U, S. Weather Bureau for the passage of the storm, and a 

 velocity of 76 miles per hovir, the sustained wind velocity over 

 most of the Narragansett Bay area, was selected as the design-stoim 

 velocity. The storm-tide potential at the entrance to Narragansett 

 Bay was determined, including a preliminary estimate of the height 

 of the surge after its propagation along the coast and up Block 

 Island Sound to the entrance of Narragansett Bay, 



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