39 



The more usual problem of wave refraction is that of a wave advanc- 

 ing to a curving shore line over a mUdly irregular bottom. The 

 methods outlined probably are inapplicable to abrupt changes in 

 depth. The limitation, which can be stated only in very general 

 terms untU experimental results are available, is that the change in 

 depth should be a small percentage of the depth in a distance equal 

 to one wave length. 



The problem requires graphical solution and the method employed 

 is very nearly the same as for light and sound waves in which each 

 point on the wave front is considered as a radiating center. 



The time increment is usually taken as an integral multiple of the 

 wave period. The accuracy of the diagram is increased by decreasing 



REFRACTION OF WAVES APPROACHING 



A SHORE 



SHORE 



Figure 14. 



the time interval. The criterion in choosing the time interval is that 

 the difference in depth at the initial and final wave positions is a 

 small percentage of the depth. It is seldom necessary to consider 

 variations in tidal elevation in constructing these diagrams and the 

 effect of finite wave height on wave velocity is neglected. 



The wave height is obtained from a consideration of 'the power 

 transmitted. If the wave crest in deep water is broken up into equal 

 increments of length, lines drawn from the points of division and 

 orthogonal to all of the wave crests will represent surfaces across 

 which no power flows. The initial power is computed from the period 

 and height by means of equations 2c and 34. On the assumption 

 that frictional dissipation is negligible, the power per unit of crest 



