336 



Tides and Tidal Currents in the Proximity of Land 



Depth (m) 1 5 10 20 30 



v in g cm -1 sec" 1 1140 1720 1250 952 75 



The order of magnitude agrees with the values found by Sverdrup. 



The current observations published by Defant and Schubert (1934) made 

 during 7 tidal periods by four ships of the Kattegat expedition in August 1931 

 were used for the study of the vertical distribution of the tidal currents. One 



-3 -2 



(a) 



Mean current ellipses 

 semi diurnal tide 



for 

 -5 m a. 2 5 -30 m 



(b) 

 Theoretical distribution 

 for Om a. 25m 



Fig. 140. Current diagrams in the southern Kattegat, August 1931. 



obtains a better picture by computing mean values for all periods and all ships. 

 The current ellipses, in all depths, rotate cum sole. Neglecting the ellipse 

 at 17 m depth, they become narrower with increasing depth; at 5 m the ratio 

 of the axis was 51, at 25-30 m about 0-24. There is also the priming of 

 the phase with increasing depth, which conforms with the theory. The main 

 results are given in Table 38, whereas in Fig. 140 are reproduced the two 

 middle diagrams. Below is the theoretical distribution of the current com- 

 puted for a coefficient of friction v = 100. The similarity of these two fig- 

 ures is apparent; the size of the current diagrams in the lower layer is, ac- 

 cording to the observations, approximately twice the size of the computed 

 one. The cause of this might be the discontinuity layer between 13 and 17 m. 

 Grace (1929, p. 150) has investigated the influence of the friction by other 



