31 



ranges and elevations at gages located downstream from the barriers were 

 relatively unchanged^ while tidal ranges at stations upstream from the 

 structure were reduced by about U5 to 50 per cent (the elevations of 

 high water being lowered and those of low water being raised) . The maxi- 

 mum elevations of hurricane tides upstream from the structure were low- 

 ered by amounts ranging from about 9«0 ft at Warwick to about 11.1 ft 

 at Providence. Downstream from the structures, however, the elevations 

 of hurricane tides were increased by amounts ranging up to about l.U ft. 

 The results of this test indicate that barriers located in this region 

 of the bay would reduce hurricane tide elevations at all locations up- 

 stream from the barriers but would cause an appreciable buildup downstream 

 from the structures over elevations without barriers. 



42. Tests of the Middle Bay barriers were also made with the East 

 Passage navigation opening closed, thus completely closing off the upper 

 part of the bay. This condition was designated plan 23 of the model 

 study, and the same conditions of astronomical and hurricane tides were 

 used for this test as for tests of plan 22. 



k3' The effects of plan 23 on hurricane tide heights at gages 

 located downstream from the structures are also shown in table 1, to- 

 gether with the effects on times of high tide. No tidal data are pre- 

 sented for gages located upstream from the structures, since that portion 

 of the bay system was not subject to tidal influence for conditions of 

 complete closure of the structures. As in the case of plan 22, reliable 

 measurements of astronomical tide ranges and elevations were made at 

 only a few locations; these measurements indicate that tide ranges and 

 elevations at gages located downstream from the barriers for plan 23 

 were essentially the same as for the base test. The maximum elevations 

 reached by hurricane tides were increased over those of the base test 

 at gages located downstream from the barriers, the maximum increases be- 

 ing just downstream from the West Passage and East Passage structures 

 and in the Sakonnet River. These measurements show that the buildup 

 downstream from the barriers would be slightly more severe for plan 23 

 than for plan 22 (maximum of about 2.0 ft for plan 23, compared to about 

 l.U ft for plan 22). 



