MEMORANDUM CONCERNING THE WATER DEPTH AND WAVE 

 ANGLE AT THE POINT OF BREAKING 



Methods in use for determining the water depth and the angle between 

 the wave crest and the depth contour, at the point at which waves break, 

 appear to be susceptible to some simplification for straight shore lines. 

 Only the breaker condition is desiredo The quantities given by the fore- 

 cast are oc Q s T, and H Q o The refraction coefficient, k or H /H , is a 

 function of oc and d/l^ only. Using these quantities and the experiment- 

 ally determined breaking conditions from Plate I of "Breakers and Surf, 

 Principles in Forecasting", H. 0° No, 234* the curves are as shown in 

 Figure 1 



The method of solution is to assume values of (d^/T^) and obtain 



_ o from the curve for the pertinent value of cx Q . Multiply the true 

 H 



value of ?° by Ji!° and compare with the value of r H o ,u>- At the 

 W H \ 2> 



breaking condition, 



ij2 ij2 H 



As an example of the method, assume the following conditions: 

 «o = 40° 





H o 



= 



5 



ft. 





T 



- 



10 sec 



Therefore 













H 



- 



0, 



.05 





•jS 









By trial and error. 



Assume 



VT 2 CH /*)b ( £o_, ( |o )x( 5V) 



0.10 0.052 0.88 0.044 



0.09 0.044 0.88 0.044 



The correct value of d^T 2 , therefore, is 0.09 and the corresponding 

 values of other terms are: 



29 



