162 BREAKER DIRECTION AND HEIGHT 



are approximately parallel with the coast of the central sector of a 

 short, wide, and evenly rounded beach (and sandy beaches usually 

 do face the prevailing direction from which the largest waves come) , 

 the breakers are not likely to differ enough in height around its shore- 

 line for landing to be easy anywhere along it, if the surf is dangerous 

 along its central part. When the waves are advancing on a beach 

 of this shape at a wide angle — or advancing directly on a more deeply 

 concave beach — the reduction in the heights of the breakers by refrac- 

 tion may be great enough to make landing possible on the more shel- 

 tered flank in the one case, or on both flanks in the other case, if the 

 waves offshore are steep and not more than 6 feet or so high. But this 

 is not to be expected if they are much higher than that, or if they are 

 the product of a swell, the initial steepness of which is small. 



The situation is different for long, narrow bays, where there may 

 be no surf at all at the head, even when the waves driving in are so 

 large that they cause heavy breakers at the mouth on both sides. We 

 believe the reason to be that the ends of the wave crests break more or 

 less along one or both shores in their advance up the bay while their 

 central sectors are still far away from the head of the bay. And since 

 the waves expand sidewise to compensate for being "worn off" in this 

 way at the two ends, they decrease correspondingly in height. If a 

 bay of this character is long enough, compared to its breadth, the waves 

 may be drained of so much of their energy in this way that they cause 

 only a weak swash on the shore by the time they arrive at the head, 

 i. e., just where the surf is usually heaviest in a crescent-shaped bay. 

 In this connection, we think of St. Mary Bay, Nova Scotia (fig. 48), 

 which is about 8 miles broad at its entrance by about 30 miles long, 

 but which offers safe anchorage and easy landing for small boats at its 

 head at most times, although it is wide open to storm seas, or to swells 

 coming from offshore. And many other long, narrow harbors in vari- 

 ous parts of the world owe their safety to their shapes, in this same way. 



Thfe generalization might seem (at first reading) to contradict the 

 statement, commonly made, that waves, running up a narrow, funnel- 

 shaped, and steep-walled indentation of the coast, are condensed side- 

 wise as the sides of the cove draw together, so that their heights are 

 increased. Indeed the waves should (theoretically) double in height 

 by the time they reached the point where such a bay was only one- 

 fourth as wide as at its entrance, provided that its bottom were deep 

 and perfectly level from side to side so that the shapes of the waves were 

 affected by the shape of coast, alone. The breakers that sometimes 

 spout in the air at the head of a narrowing chasm, in a rocky coast, 

 afford a spectacular illustration of this principle. And the difficulty of 

 landing may increase, for this reason, toward the head of a very nar- 

 row and steep-walled cove, into which a sea is heaving directly. But 



