EFFECT OF BARRIERS ON NORMAL CONDITIONS 



B-28. OaiERAL 



Preliminary tests of the effects of the tidal barriers on 

 present oceanographic conditions were made in the hydraulic model 

 of Narragansett Bay after the model was adjusted to reproduce exist- 

 ing tides and currents. Basic information on present conditions in 

 the bay was derived from the considerable data on ten^jeratTires, 

 salinities, flushing rates and silting in the bay collected during 

 1956 by the Narragansett Marine Laboratory and from observations 

 of the U.S. Coast and Geodetic Sxirvey. 



The effects of the Lower Bay barriers on present oceanographic 

 conditions, such as tides, currents, temperature, salinity, flushing, 

 sedimentation, fisheries, pollution and navigation, are exceedingly 

 conplex and will require extensive investigation over a period of 

 years. As a result of these studies, the navigation openings in the 

 barriers may be enlarged and sluice gates provided >iiich would 

 greatly diminish the effect of the barriers in restricting tidal 

 circulation. The results of the preliminary studies are indicated 

 below under appropriate headings. 



B-2>, TIDES 



The model indicated that the Lotrer Bay barriers would reduce 

 tho normal tide range at Providence by about 35 percent. This re- 

 duction occurs as a loxrering of the high tide level by about 0,8 

 foot and the raising of the low tide level by a similar amount. 

 No appreciable effect on the nomial tide range would be caused by 

 the Fox Point barrier, 



B-30, CURRENTS 



The Lower Bay barriers, with the exception of the Tiverton 

 barrier, were tested in a flume using an undistorted scale model 

 to determine the effects of normal tidal currents through the 

 navigation openings. The tests indicated that currents through 

 the navigation openings would increase in velocity from slack water 

 for a period of about 3 hours until the maximum velocity of 1; to 5 

 knots is reached (as compared with a maximum velocity of 1.5 knots 

 under normal conditions) • The velocity would then decrease for 

 another period of about 3 hours when slack water is again reached 

 and the current begins a similar cycle in the opposite direction. 



B-28 



