560 



THE POPULAR SCIENCE MONTHLY 



clilfs, now grass covered, may be seen at these points. But the bar 

 now lies a short distance in front of these old cliffs, and protects them 

 from erosion. Shrewsbury and Navesink Eivers are really bays of the 

 ocean formed by a sinking of the land or a rising of the ocean level 

 which permitted the seawater to flood pre-existing river valleys. They 

 are " drowned valleys/' but not " rivers " in the true sense of the term. 



Ill order fully to appreciate the effects of storms upon the New 

 Jersey coast, it is necessary to keep in mind some of the conditions 

 affecting wave energy. The destructive power of a wave depends in 

 part upon its size, and this in turn partly upon the water depth. 

 Waves usually break and dissipate their energy when they come into 

 w-ater of a depth equal to the wave height. Hence, the deeper the 

 water immediately at the shore the larger the waves which can attack 

 it, and the greater the damage they will effect at that point. It follows 

 from this that the rise of the tide must increase the destructive power 

 of storm waves on the coast, not only because it brings the zone of 

 wave activity farther in upon the shore, but also because the deepening 

 of the water as the tide rises against the steeper upper part of the 

 shore profile permits larger and more powerful waves to break against 

 the shore cliffs. In all the recent storms the chief damage to the New 

 Jersey coast occurred at the high-tide periods, and the citizens worked 

 feverishly during low Avater to prepare for the violent wave attack which 

 they knew would ensue at the next high tide. 



On-shore winds increase the destructive power of the waves in a 

 variety of ways. First of all, they raise the water level by blowing the 

 surface of tlio sea along the coast faster than the water escapes seaward 



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Nti UNDEKMINED FROM REAR. 



