352 



Tides and Tidal Currents in the Proximity of Land 



ats = tan 



_j tanh^.v 

 tamo- 



tan 



_iA* 



(XI. 28) 



This function relates the time of slack water to any position along the channel 

 for any chosen coefficient of damping. The time of maximum current will 

 precede or follow the time of slack water by one-quarter period or 90°. 



Tidal data are available in the form of records of the time of H.W., the 

 elevation at H.W. and the time of slack water or maximum current at various 

 positions along the channel. We have now the posibility to test these equations 

 on the tidal data. This will give us indications to the effect of a given channel 

 on the primary or reflected wave; information on the distribution of phase 

 differences along the channel and on the damping which is required. These 

 applications are to be tested with the same restrictions as discussed previously 

 in this chapter. By combining these relations defined by equations (XI. 26 

 and 27) Fig. 144 was constructed in which the observed variables (the 



20° -140° -160° -180° 



PHASE DIFFERENCE RELATIVE TO POINT Of REELECTION Ki 



Fig. 145. Relations of the time angle between high water at H , and slack water at H at any 

 point along a channel, the phase difference of a primary wave at that point relative to the 

 barrier y.x and the coefficient of damping //, when reflection occurs at a barrier where xx = 0. 



ratio of the H.W. elevations y\\-y\q on a logarithmic scale and the local time 

 of H.W. at H ) are represented by the rectangular co-ordinates and the desired 

 properties of incoming wave (the phase relations and the coefficients of 

 damping) are represented each by a series of curves. This nomogram is 



