53. THE HUHRIOaME FLOOD PROBLEI>I 



The engineering problem of hurricane flood protection in Narra- 

 gansett Bay is one of selecting a feasible structure or combination 

 of structures which will provide economically justifiable protection 

 for as large a part of the bay's 250 mile shoreline as practicable, 

 with a minimvim disruption of existing or potential navigational, 

 industrial and commercial, residential and other interests in the 

 area. Review of the possible alternative methods of hurricane tidal 

 flood control in the area indicates that while, at first glance, 

 individual structures at the most seriously affected localities 

 might appear most economically justified, the cost of these structures 

 tends to be prohibitive, or their effectiveness doubtful. Since, at 

 best, local structirres such as dikes, walls, breakwaters, b\ilkheads, 

 or small barriers can protect only a few miles of shoreline, the 

 tidal flood damages which they prevent are greatly exceeded by their 

 costs, except in limited areas of very high concentration and valua- 

 tion of property, as in Providence, Conversely, although the costs 

 of large-scale bcirriers are very high, the reduction in damages 

 accruing t« them tends to make them economically justifiable be- 

 cause of the great length of shoreline which a single barrier, or 

 series of inter-related barriers, vrill protect. 



Since nearly two-thirds of the very heavy hurricane tidal flood 

 damages incurred in Narragansett Bay are distributed over a variety 

 of localities; exclusive of Providence, along the nearly 2^0 miles 

 of shoreline, it is clear that large-scale barriers vrill tend to be 

 Tiore economically justified than local protective structures. In 

 view of this, the engineering problem of protection resolves itself 

 into one of determining that barrier site and design or combination 

 of barrier sites and designs which is most practicable from an engi- 

 neering "ooint of vievr, and which will offer economically justifiable 

 protection for the maximum area, 



5Il, STUDIES OF ALI-ERNATIVE BARIGER, PUNS 



Preliminary studies were made of the 1$ plans proposed by local 

 interests, and listed in paragraph k9» -^H of these plans are essen- 

 tially for tidal flood barriers at various sites within the bay. 

 After studies of these proposals, the following general consideraxions 

 governing the selection of sites and designs of tidal flood barriers 

 in Narragansett Bay were developed, 



a. Considerations governing selection of barrier sites . 

 It is self-evident, of course, that the selection of barrier sites 

 will be governed by considerations of necessary length, water depth. 



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