^7 



because of extreme turbulence in those areas. 



68. Plan 36 was identical with plan 35 except that the West Passage 

 barrier was moved downstream about 3*0 miles from the Jamestown Bridge 

 (see fig. 15); the sizes of navigation openings for plan 36 were identical 

 with those of plan 35 (see fig. I8) . Astronomical tide tests were made of 

 plan 36 for conditions of both spring- and mean-tide ranges, and hurricane 

 tide tests were made for conditions of the astronomical spring tide in 

 combination with the 1938 hurricane tide and the 20-knot design hurricane 

 tide. Current velocities were measured in the East and V/est Passage navi- 

 gation openings in the model for conditions of both spring tide and mean 

 tide; however, velocities were not measured at stations throughout the bay 

 for this plan, nor were supplementary velocity measurements made in the 

 flume. Inasmuch as plan 36 was so similar to plan 35^ it was considered 

 that the detailed velocity measurements made for the latter plan would 



be adequate to show the effects of plan 36. 



69. The effects of plan 36 on astronomical tide ranges and eleva- 

 tions for conditions of both spring and mean tides are shown separately 

 in table k; the effects on elevations of hurricane tides are shown in 

 that portion of table h presenting astronomical spring tide data, since 

 the hurricane tide tests were made in combination with that tide. The 

 effects of plan 36 on the times of both astronomical and hurricane high 

 tides are shown in table 3- Astronomical tide ranges at gages upstream 

 from the Lower Bay barriers were reduced by an average of about k2 per 

 cent for conditions of spring tide and by an average of about kO per cent 

 for conditions of mean tide. These average reductions in astronomical 

 tide ranges upstream from the Lower Bay barriers are slightly greater 

 than occurred for plan 35 and are believed attributable to the slight 

 increase in surface area upstream from the barrier resulting from reloca- 

 tion of the West Passage barrier. 



70. Plan 36 reduced hurricane tide elevations at Providence from 

 +15.1 ft mlw We■^^^port to +6.0 ft for conditions of the 1938 hurricane tide 

 and from +YJ.2 ft to +7-1 ft for conditions of the 20-knot design hurricane 

 tide. Hurricane tide elevations at Providence were slightly lower for 

 plan 36 than for plan 35^ and this effect is also believed attributable 



