3-72 



is the maximum rate of change of the elevation of the sea surface. Since 

 the current is approximately 90° out of phase with the tide height, 



dt 



max 



occurs at same time as maximum tidal currents. The cross-sectional area 



3 2 

 of Transect 1 is 7.9 x 10 m ; therefore, assuming the current is perpen- 

 dicular to the transect, the average maximum velocity through Transect 1 

 is: 



(1.35 X 10~^m/s) (2.7 x lO^m^) „ ^ 



_ 4_g cm/sec 



3 2 



7.9 X 10 m 



where 2.7 x 10 m is the surface area of region A (Figure 3.4-8) at mid- 

 tide. The spatial average of the current through Transect 1 in cm/sec 

 can be represented as : 



. ^ Z-n-t 

 V avg = 4.6 cos ^ — ;; — 

 ^ 12.4 



The root-mean- squared velocity is 0.707 times the amplitude; 

 therefore, during flood or ebb tide, the average momentum of the water, 

 integrated over the cross-sectional area of Transect 1 is: 



(4.6 X 10~^m/s) (.707) (7.9 x lo\^) (1.02 x 10^ Kg/m^) = 2.62 x lo\g/ 



The momentum at Transect 1 due to the discharge from the 

 station, integrated over the cross-sectional area of the discharge pipe 

 is: 



(17.7 m'/s) (1.02 x lo\g/m"^) = 1.8 x lo\g/s 



Thus, the contribution of the tidal currents to the momentum balance 

 through a narrow transect in the inner harbor is over ten times greater 

 than that of the cooling water discharge. The relative importance of 

 tidal currents increases rapidly as one moves away from the discharge 

 point . 



