information on ten^jeratures, salinities, currents and circulation, 

 and bottom conditions. Preliminary estimates of the effects of the 

 Lower Bay barriers on these conditions were made from hydraulic 

 model tests and studies by the Narragansett Marine Laboratory and 

 other agencies, as described below: 



(2) Tidal range and currents * Model tests have shown 

 that the Lower Bay barriers would decrease the tidal range by 

 approximately one-third. Mean high tide elevation would be 

 lowered about 0.9 foot and mean low tide elsvation would be raised 

 an equal amount. Tidal currents would probably be reduced about 

 30 percent, except in the navigation openings as noted below. The 

 distribution of normal tidal currents and their direction would be 

 unaffected. The effect of the reduction in tidal range on naviga- 

 tion is discussed below. 



(3) Navigation . While the reduction in tidal range 

 woiiLd not materially affect the low-water depth of the dredged 

 navigation channels it would affect the depth available in the 

 Upper Bay for navigation and berthing of the largest commercial 

 vessels which depend on high tide. This matter may be resolved by 

 sluice gates in the barriers which would eliminate most of the 

 reduction in tidal range. At the time a final decision is reached 

 on the size of the navigation openings, it would be possible to 

 determine whether the problem of ship clearance is serious enough 

 to warrant modifying the barriers by introducing sluice gates. 



At the openings in the barrisrs maximum flood and ebb currents 

 between jU and 5 knots could be expected. This would adversely affect 

 navigation j particularly small boats of low engine power. For 

 conparison, currents throiigh the Cape Cod Canal range from 3 to 6 

 knots and at the entrance to Long Island Sound currents range from 

 3.3 to $.b knots. The navigation openings referred to mean low 

 water of 1,000-foot width by 50-foot depth in the East barrier and 

 UOO-foot width by UO-foot depth in the West barrier, are con- 

 sidered by the Navy to be inadequate to provide the requisite 

 margin of safety for Naval use under all circumstances. Negotia- 

 tions are in progress with the ^^avy on dimensions that will meet 

 their requirements and at the same time retain a high degree of 

 protection in the design. 



(ii) Tei[g)erature3 and salinity . Preliminary studies 

 indicate that the effect of the barriers on water temperatures 

 within the bay would be negligible , amounting to no more than 

 0,5°F. Norinal salinity ranges from 18 parts per thousand at 



53 



