the TTave velocity(lV) 



(13) z^iz^\{'- 3:L^^^)^^ 



which ■'•w deep v/ater - \. The mean rate of transmission of energy per 

 wave length and per unit crest width (the power) is P = n Et G . This 

 rate of transmission remains the same in both deep and shallow water 

 (Pq = P) and equating the two we have, if there is no refraction 

 Eto n^ Co = E^ N E or 



With refraction (20) the assumption is made that the power transmitted 

 between orthogonals to the wave crest remains unchanged, therefore 

 calling the ratio of the distance between two orthogonals in deep and 

 shallow water M^ /£ = K"^ . 



(^') l^rx^v^n-'---'^ 



i ?< 



For these waves the wave lengths in shallow and deep water are related 

 by L/Lq ^ tanh '-^^ , This relationship permits the calculation of 

 wave parameters in shallow water as functions of the deep water wave 

 length, and as an aid in calculation, tables of these relationships 

 have been compiled and published. Figure 4 is a curve of Hq/Ho' for 

 various values of d/L and d/Lo- 



Height of Seawall to be Fully Effective - With the aid of tho 

 relationships between shallovr and deep water wave heicji.t (Figure 4), 

 we can find the maximum wave to be expected at a seawall if it is so 

 placed that these waves would not break on attaining this depth in the 

 absence of the wall. To apply the established criterion for total 

 effectiveness of the wall, i.e. that its crost height be at least as 

 high as the crest height of the highest impinging wave we must find 

 anev/ the percentage of wave height T.liich lies above still water level. 

 The paper by K. C. Reynolds (9)^ cited before, indicates that except 

 in the immediate vicinity of the breaker zone, this percentage rarely 

 exceeds 60^. If it is determined therefore, that a seawall must be 

 placed on a slope so as to be open to attack by non-breaking waves, 

 its crest height be above (say) MLW, for total effectiveness must be 



(16) ht = ht + 0.6 H 



where ht is the height above /ILYf of the greatest expected tide, and 

 H is the greatest wave height expected. 



11 



