3-58 



Modifioation of Local Current Patterns 



The momentum of the water entering the intake structure and 

 leaving the discharge pipe must contribute to some degree to the local 

 current patterns. 



The intake structure draws cooling water from the easterly end 

 of an intake channel 230 m in length which runs from the intake struc- 

 ture to a point 30 to 45 m from the eastern edge of the main shipping 

 channel (Figure 1-3) . The intake channel was dredged to a depth of 9 m 

 below mean sea level and crosses the shallow area adjacent to the plant 

 site. Piers north and south of the plant may restrict flow that is part 

 of the main harbor circulation from entering the shallow waters surround- 

 ing the intake channel. Skimming walls on the intake structure limit 

 flow immediately in front of the structure to depths greater than 2.5 m 

 below mean sea level. It is reasonable to believe that water enters the 

 intake structure and channel from the shallow water area between the 

 piers as well as from the westerly end of the channel. During normal 



operations at 100% generating capacity with three cooling water pumps in 



3 

 operation, the design flow for the intake structure is 18 m /sec. 



Assuming conservatively that the shallow water area does not contribute 



to the condenser cooling water, all of the flow would enter from the 



westerly end of the channel; in this case impact on the main harbor 



circulation by entrainment of water which is part of that circulation 



would be at a maximum. If the flow was uniform over the cross-sectional 



area of the intake channel, current speeds of 8 cm/sec at low tide and 5 



cm/sec at high tide would be needed to deliver the cooling water to the 



intake structure at the required rate. At the westerly end of the 



intake channel, the flow into the channel would add to the tidal current 



(amplitude 21 cm/sec) as is shown in Figure 3-14. Figure 3-14, a simple 



vector addition of the intake velocities and tidal current velocities, 



shows that at the beginning of the intake channel the maximum flood and 



ebb currents would be deflected by no more than 20° from their normal 



path (parallel to the main channel) and that at slack tide a current 



