332 Tides and Tidal Currents in the Proximity of Land 



Table 37. Current data for tide waves, taking the friction into account 



(a= 1 -4052 x 10-") 



Case 1: Polar Sea, </> = 72°N., /= l-387x 10" 4 , s = 0-987, depth 



50 m, coefficient of eddy viscosity v = 182. 



Case 2: Southern Kattegat, 4> = 56°20N., /= 1-213X10 -4 , depth 

 30 m, coefficient of eddy viscosity v = 100. 



conditions change and the maximum velocities of the tide wave are then great- 

 est in the middle layers, while the velocities at the surface and bottom, are 

 zero. In nature, however, the vertical structure of the sea, for a case like this, 

 consists of three layers : the upper layer is almost homogenous and has strong 

 turbulence, a bottom layer with little turbulence, and the middle layer between 

 these two is a stable, relatively thin water layer with nearly no friction. The 

 tide waves then take the character of internal tide waves (see p. 517). 

 (d) Results of Current Measurements 



There are not many observations available to test the above-mentioned the- 

 oretical results. In making such a comparison, it should be remembered first 

 of all that the theory is based on a factional coefficient which is assumed con- 

 stant, whereas in reality this coefficient varies with depth, according to the 

 veritical density distribution. This circumstance can cause considerable devia- 

 tion, especially if several horizontal strata are present. The assumption that 

 there is on slipping motion along the bottom is perhaps not accurate in all 

 cases. For shallow water only the lower parts of the curves in Fig. 134 are to 

 be considered, where the coefficient of friction is most noticeable, but generally 



