Currents 



For about 9\ hours in a tidal cycle 

 of 12j hours, the filling gates will be 

 closed. Water will leave the high pool 

 continuously through the turbines. While 

 the filling gates are closed, the only 

 motion will be towards Western Passage 

 and will be contained mostly in the upper 

 45 feet. Mean velocities of the upper 

 layer are expected to be about one -fifth 

 of the present values. When the gates are 

 open, velocities should be similar in 

 most areas but slightly lower than at 

 present. A residual counterclockwise 

 circulation in the Bay will likely be more 

 pronounced. 



When the emptying gates are open, 

 velocities in the low pool will be similar 

 to present values at half -ebb. While the 

 emptying gates are closed, the flow will 

 spread in both directions from the low- 

 pool side of the powerhouse. During this 

 period, the velocities in Cobscook Bay 

 should be less than one -third the present 

 value west of the powerhouse and approx- 

 imately one -fifth the present value between 

 the powerhouse and the emptying gates. 

 The vertical -longitudinal circulation in 

 Cobscook Bay west of the powerhouse will 

 be an inward movement of the deeper 

 water and a seaward movement of the 

 surface layer. 



In the outside area there is little indi- 

 cation that significant changes in residual 

 flow will extend much beyond the Head 

 Harbour-Bliss Island Region. Tidal 

 streams should be reduced in the ap- 

 proaches to the passages and increased 

 in other areas of the Quoddy vRegion. The 

 direction of tidal streams will be altered 

 only slightly, and changes in speed are 

 not expected to exceed 20 percent of their 

 present value. For about 6 hours in 

 12|, speeds inside the Head Harbour- 

 Bliss Island line will be very snaall. 

 When the filling gates are open, flow in 

 the Bliss Island region should be similar 

 to that at present, but reduced slightly 

 in the Head Harbour region and increased 

 in the channel between Indian Island and 

 Deer Island. Most of the water entering 

 the Western filling gates will be water 

 that has drained from the low pool. Inflow 

 through the Letite filling gates will be 

 mostly "new" water from outside the 

 dams. Residual flow, which will be more 

 marked than at present, will be inward 



toward Letite Passage amd outward from 

 Head Harbour Passage. Wind speed and 

 direction should play an important role 

 in controlling the amount of water recir- 

 culated through the Letite gates. 



Water temperature 



Reduced velocities in the high pool 

 will result in decreased vertical mixing, 

 permitting increased stratification, and 

 hence greater seasonal variations in the 

 temperature of the surface waters. These 

 variations will be minimum near the 

 Letite filling gates (altered only slightly 

 from present conditions) and maximum 

 along the north shore of Passamaquoddy 

 Bay and in the St. Croix estuary. Maxi- 

 mum summer temperatures at the sur- 

 face are likely to be in the vicinity of 

 68° F. The surface layer will probably 

 be less than 10 feet in depth most of the 

 time, but on occasion may deepen to 30 

 to 50 feet. Below this depth, temperatures 

 will be altered only slightly, with the 

 expected range falling within 32° F. and 

 56° F. Ice cover is expected to occur 

 over part of the Bay in winter. 



Stratification will not be as marked in 

 the low pool as in Passamaquoddy Bay, 

 except in the upper reaches. Summer 

 maximum at the surface in the inner part 

 of the Bay may reach 68° F. The outer 

 area is unlikely to exceed 60° F. Summer 

 temperatures of the bottom water may 

 increase by 4° to 5°, while winter tem- 

 peratures will be lowered only slightly. 

 Ice cover is likely to occur in the inner 

 part of the Bay during the winter. 



Little change is expected in the outside 

 area except contiguous to the emptying 

 and filling gates and mostly inside the 

 Head Harbour-Bliss Island line, where 

 a somewhat greater seasonal variation 

 is expected. 



Salinity 



Mean surface salinity in the high pool 

 will be lowered. Bottom salinities should 

 be altered only slightly. During freshets, 

 surface salinity may drop below 20 parts 

 per thousand (normal sea water in the 

 Bay of Fundy is approximately 33 parts 

 per thousand). At other times of the year, 

 surface salinity should be between 20 and 

 30 parts per thousand, except in the St. 

 Croix estuary above St. Andrews and in 



26 



