33 



Lower Bay barrier)^ either complete or partial closiire of the Sakonnet 

 River at Old Stone Bridge, and the diking of low marsh areas on Conanicut 

 Island. Navigation openings of various depths and widths were considered 

 for the East Passage, West Passage, and Sakonnet River structures, and 

 each combination of openings was assigned a test number for identifica- 

 tion purposes. 



k6. As in the case of the Middle Bay barriers, initial tests of 

 the Lower Bay barriers were made for conditions of the extreme astro- 

 nomical spring tide range of 5-^ ft at Newport to determine an approx- 

 imate arrangement of navigation openings to satisfy the conflicting re- 

 q^uirements of (l) reduction in hurricane tide elevations at Providence, 

 (2) minimum width of opening specified by the Navy, and (3) reduction 

 of maximum current velocities to those that can be tolerated by naviga- 

 tion. Inasmuch as all these criteria were varied over a wide range dixr- 

 ing the course of the model study, this report makes no reference to 

 the widths and/or velocities that would be acceptable but only presents 

 data for the various conditions tested in the model. On the basis of 

 the preliminary tests, a Lower Bay barrier plan (designated plan 29 of 

 the model study) was devised and subjected to complete testing. It is 

 pointed out that the refined model roughness adjustment was accomplished 

 prior to the testing of plan 29 as well as all subsequent plans reported 

 herein. 



k"] . The locations of the various components of plan 29 were as 

 described in paragraph i+5, and openings for navigation were provided in 

 the West Passage and East Passage structures as shown on fig. YJ . The 

 Sakonnet River closure at Old Stone Bridge also had a navigation opening. 

 The West Passage opening had a sill elevation of -ko ft mlw and a sill 

 width of 600 ft; the East Passage opening had a sill elevation of -50 ft 

 mlw and a sill width of 1000 ft; and the Sakonnet River opening had a 

 sill elevation of -30 ft mlw and a sill width of 100 ft. The abutment 

 slopes of the East and West Passage openings were 1.0 vertical on I.5 

 horizontal, the slope of the ocean side of the structures was 1.0 vertical 

 on 2.0 horizontal, and the slope of the bay side was 1.0 vertical on I.5 

 horizontal. The Sakonnet River opening had vertical sides and was equipped 



