1^0 



hurricane tides) for these plans were identical with those of plan 30. 

 The results of tests of these plans are presented in numerical order 

 in tables 3 and k; however^ in the interest of clarity _, the test results 

 are presented in the following discussion in the order of descending 

 total area of the navigation openings (plan 33^ 32; 31^ and 3^^ in that 

 order) . Plan 32 was not subjected to tests in the model; instead, the 

 effects of this plan on tidal ranges and elevations were interpolated 

 from the results of tests of other plans in this series. 



59* The effects of the plans on astronomical tide ranges and eleva- 

 tions , and on hurricane tide elevations, are shown in table h, and their 

 effects on times of high tide for both astronomical and hurricane tides 

 are shown in table 3. All of the plans reduced astronomical tide ranges 

 at gages located upstream from the Lower Bay barrier, the average re- 

 duction being of the order of l6 per cent for plan 33 ^ 32 per cent for 

 plan 31; and 37 pei" cent for plan 3^j the average reduction in range in- 

 dicated by plan 30 was about 23 per cent. Based on equivalent areas of 

 navigation opening, it was interpolated that plan 32 would have reduced 

 astronomical tide ranges upstream from the structure by an average of 

 about 19 or 20 per cent. 



60. Maximum hurricane tide elevations at Providence for conditions 

 of the 1938 hurricane tide were +8.7 ft mlw for plan 33, +7.2 ft for 

 plan 3I; and +7.1 ft for plan 3^. The maximum elevation for plan 30 was 

 +7.9 ft, and the interpolated elevation for plan 32 at Providence was 

 about +8.3 ft. For conditions of the 20-knot design hixrricane tide, the 

 maximum elevations at Providence were +10. U ft mlw for plan 33 and +8.6 

 ft for plan 3I; a test of plan 3^ for this condition was not included in 

 the testing program. The maximum elevation at Providence for plan 30 for 

 conditions of the 20-knot design hurricane tide was +9.I ft mlw, and that 

 interpolated for plan 32 was about +9.7 to +9.8 ft. No current velocity 

 measurements were made in the navigation openings of the barriers diuring 

 tests of this series of plans. 



Final combination barrier plans 



61. The results of tests of plans 30 through 3^ indicated that the 

 minimum size of navigation openings considered (71,c6o sq_ ft for plan 3^) 



