For shallow-water waves near breaking, the velocity near the crest 

 approaches the celerity o£ wave propagation. Thus, as a first approxima- 

 tion the horizontal velocity near the breaker crest is 



(7-61) 



where H^, is taken approximately equal to dj,, the depth at breaking. 

 Using Equation 7-61 for the horizontal velocity, and taking C^^ = 1.75, 

 the force per unit length of pile near the breaker crest becomes 



^Dm "^ C^ -:; P^^Lst * 0.88 pg DH^ . 



(7-62) 



Table 7-5 is a comparison between the result calculated from Equation 

 7-62 with measurements by Ross (1959) on a 1-foot diameter pile 

 (R^ * 1.3 X 10^). 



Table 7-5. Comparison of Measured and Calculated 

 Breaker Force* 



* Values given are force per unit length of pile near breaker crest. 

 t Calculated from Equation 7-62. 

 X Measured by Ross, 1959. 



Based on this comparison, the choice of C^ = 1.75 for Rg > 5 x 10^ 

 appears justified for calculating forces and moments due to breaking 

 waves in shallow water. 



7.3110 Calculation of Forces on Noncircular Piles . The basic force 

 equation (Equation 7-13) can be generalized for piles of other than 

 circular cross section, if the following substitutions are made 



7rD2 



volume per unit length of pile 



(7-63) 



where 



D = area perpendicular to flow direction per 

 unit length of pile. 



7-125 



