(h) n A theoretical curve showing the fraction of energy advanc- 



ing with the wave at a given relative depth,, The value of 

 n is used in computing H/H' . 



Determination of Wave Height and Depth of Water at Point of Breaking ; 

 All the curves on Plate 10 (Plate III from Breakers and Surf) deal with 

 waves that approach a shore line directly, so that there are no changes 

 due to refraction» When waves approach a shore line at an angle, the re- 

 fraction correction first must be applied. Plate 10 is used in forecast- 

 ing and in the interpretation of aerial photographs <> 



Given values of H ? and T define a point for which corresponding 

 values of H, and d, are found by interpolation between the solid and dashed 

 lines s respectively- To find the wave length or velocity at the breaking 

 depth, d^, or at any other depth, enter the inset with this value of d, 

 follow horizontally to the proper value of T, and read off L on the top 

 scale o The velocity is then found from the ratio C = L/T. 



Measure the wave length, L, at any depth, d (not necessarily the 

 breaker depth), and find T from the inseto Enter the main graph with T 

 and follow a vertical line to the proper value of dv . Head off H^ from 

 the solid lines and H« from the scale to the left or right of the 

 diagram o 



Effect of Capillarity on Wave Velocity ^ Plate 11 is a plot of curves 

 showing the effect of capillarity on wave velocity. Y/ave velocity has been 

 plotted as a function of wave length both with and without surface 

 tension effects. The per cent error or per cent difference between the 

 velocity as determined by the two velocity equations also is plotted as a 

 function of wave length. It is to be noted that for a wave length greater 

 than 0.4- feet, the error in neglecting surface tension effects is less than 

 one per cent. 



Effect of Refraction on Wave Direction ; Plates 12 and 13 show the 

 effect of refraction on wave direction. They give the angle «c between 

 the wave front and the bottom contours in shallow water for given values 

 of the ratio, d/Lo, as a function of the angle «: e in deep water between 

 the wave front and the contours. This relationship is derived from Snell's 

 law; that is: 



sinog = C_ 



sinoco G (13) 



where C is the velocity in shallow water and G is the velocity in deep 

 water. For given values of d/Lg, C/0 o can be found from Plate 9, soec 

 can be plotted for various values of <=c . Plate 12 covers the range 

 of d/L from 0.0 to 0.5. Plate 13 is a larger scale drawing of the region 

 d/L Q between zero and 0.1. 



The curves on Plate L4 (Plate II, Breakers and Surf) give the effect 

 of refraction on wave height and direction for waves approaching at an 

 angle toward a straight shore line where the bottom contours are straight 

 and parallel to the shore. The horizontal scale is d/to, the relative 



