MOVEMENTS OF SEA-WATER 



175 



Fig. 177. Shore wave breaking on east wall of Hastings. (From Wheeler's 

 Thr Si-ii Coast; by permission of Longmans, Green and Company.) 



in the crests of waves is accomplished by a current along the bot- 

 tom, called the imderlow, which is sensibly normal to the coast when 

 uninfluenced by oblique waves. 



When waves advance on shore obliquely, a shore-current is 

 developed as illustrated by Fig. 178, where ab represents the direc- 

 tion of the incoming wave, be the direction of the shore (or littoral] 

 current, and bd the direction of the 

 undertow. Where they strike the bor- 

 ders of land, the wind-waves, there- 

 fore, generate two other movements, 

 the undertow and the littoral current. 

 Any particle of water near shore may 

 be affected by any two or by all three 

 of these movements at the same mo- 

 ment. The effect of littoral current 

 and undertow is to give a particle of 

 water on which both are working '^ 

 direction between the two, as be. The 

 effect of other combinations is readily 

 inferred. These various combinations 

 are of consequence in the transporta- 

 tion of debris. Waves and the move- 



Fig. 178. Diagram showing 



relative (linvtions of wave, 

 undertow, and shore-current. 



