b. Lower Bay barriers . The size of the navigation opening 

 and the vertical clearance required would make a highway crossing 

 of the Lower B^ barriers expensive. Such a crossing at the 

 Tiverton barrier would not be necessary, because of a newly 

 constructed highway bridge less than one mile upstream, 



62. DEGRfifi OF PROTECTION 



The Fox Point barrier, as the first unit of the plan to be 

 constructed, would provide full protection for the center of 

 Providence. The Lower 3ay barriers, to be constructed later, 

 would afford general protection to the bay and practically 

 eliminate high-water damage from floods equal to those of 1938 

 and 19Sh, although some wave damage would remain, particularly 

 in the upper bay area. However, the degree of protection pro- 

 vided by the Lower Bay barriers will depend on the dimensions 

 of the navigation openings, which are subject to adjustment in 

 final design studies. The degree of protection which wo\ild be 

 provided by each unit of the plan is set forth in further detail 

 below: 



a. Protection by Fox Point barrier . At the time of a 

 hvirricane warning, sluice gates in the barrier would be closed 



as near to low tide as practicable and pumps operated to maintain 

 the pool level above the barrier below mean sea level. In the 

 event of the combination of the design stream flow from the 

 w'oonasquatucket and Moshassuck Rivers coincident with the design 

 tidal flooding from the bay, a very unlikely occurrence, the 

 pool level might rise as high as 3 feet above mean sea level, 

 which is well below the zero damage elevation of 6.7 feet above 

 mean sea level. 



b. Protection by Lower Bay barriers . The effectiveness 

 of the Lower Bay barriers in reducing hurricane tide levels has 

 been based mainly on the data provided by the hydraulic model of 

 Narragansett Bay constructed at the Waterways Experiment Station 

 in Vicksburg, Mississippi. Using prototype data from hurricanes 

 of record, the model has reproduced both normal and hurricane 

 tides with and without barriers in place. In the model, the 

 Narragansett Bay area has been reproduced to a horizontal scale 

 of 1 to 1,000 and a vertical scale of 1 to 100. Movement of the 

 tides are reproduced on a time scale of 1 to 100 so that the 

 normal astronomical tidal cycle of 12. U hours in the bay is 

 reproduced in about 7.5 minutes. A tide generator is used to 

 simulate normal ocean tides, the rise and faU of water levels 



