29 



This plan involved a structure across the West Passage between Pojac 

 Point and Patience Island (designated West Middle Bay barrier)^ a struc- 

 ture closing the gap between Patience and Prudence Islands^ a dike 

 across the Prudence Island marshes^ and a structure across the East Pas- 

 sage between Prudence and Aquidneck Islands (designated East Middle Bay 

 barrier) . The model structure in the West Passage was equipped with 33 

 sluice gates, each 100 ft wide, and that in the East Passage with 3^ 

 similar gates (see fig. l6) , in addition to navigation openings in each 

 passage. A number of preliminary hydraulic tests were made to determine 

 the maximum current velocity that would obtain in both navigation open- 

 ings with various numbers of sluice gates open in each barrier. The data 

 from these tests were to be used to determine the total area of openings 

 (both sluice gates and navigation openings) required to hold current 

 velocities in the navigation openings to a maximiom of about ^.25 ft per 

 sec for conditions of an extreme astronomical spring tide range of 5-^ 

 ft at Newport. It was found that a total opening area of about 11^1,000 

 sq ft would be required to meet this criterion. Wo structure was in- 

 stalled in the Sakonnet River during these tests. 



kO. Two degrees of closure of the Middle Bay barrier were tested 

 to determine the effects of the structures on hurricane tides. The first 

 of these, designated plan 22 of the model study, involved complete closure 

 of the V/est Passage, complete closure of the Sakonnet River at Old Stone 

 Bridge, closure of the channel between Patience and Prudence Islands, 

 and a navigation opening in the East Passage barrier having a sill eleva- 

 tion of -UO ft mlw, a sill width of 600 ft, abutment side slope of 1 on 

 1.5, and a crest elevation of +2k ft mlw. Details of this navigation 

 opening are shown on fig. l6. The hurricane tide test of plan 22 was 

 made for conditions of the 19^8 hurricane tide superimposed on the 

 astronomical spring tide having a range of U.l ft at Newport. 



Ul. The effects of plan 22 on maximim elevations of hurricane 

 tides throughout the bay system are shown in table 1, together with the 

 effects of the plan on the times of hurricane high tides. Only a few 

 reliable measurements of astronomical tide ranges and elevations were 

 made during the test of plan 22j these measurements indicate that tidal 



