77 



drift leads to an altered distribution of density and the 

 development of corresponding currents. In the northern hemis- 

 phere, the wind drift at the surface is directed 45° to the 

 right of the wind and with increasing depth, the angle between 

 the wind and the current increases while the velocity decreases. 

 If the current at equal depths is represented by an arrow of 

 the correct direction and a length corresponding to the velocity, 

 these arrows will form a spiral "staircase", the steps of which 

 become shorter as the depth increases. Thus, a depth can 

 theoretically be found at which the current flows in a direction 

 opposite to that of the surface current. However, at that 

 depth the velocity approaches zero. Such a theoretical condi= 

 tion can only develop, however, in the open ocean in regions 

 where the wind blows with a constant velocity and direction 

 over wide areas. No such simple application can be used in 

 shallow coastal waters where wind velocities and directions 

 change continuously throughout the day and where there are 

 countless modifying features caused by the shoreline, shoal 

 water, tidal effects, and unequal heating in the nearshore 

 zone. 



Near coasts the secondary effect of the wind becomes impor- 

 tant and dominant. A wind blowing parallel to the coast, with 

 the land on the right hand side looking downwind, leads to the 

 transport of light and warm surface water toward the coast. 

 The coast acts as a barrier so that the light and warmer water 

 piles up against it, and at some distance denser and colder 

 subsurface water must rise to replace that carried to the coast. 

 The distribution of density is altered and a current develops 



