head is: 



B 



or double the velocity head of the streanio As Morosi, Savart and 

 BLdone have demonstrated theoretically and proven experimentally, in 

 the initial instant (or -when the first liquid molecules strike the 

 plane) this pressure is doubled and ttie head becomes 



g 



According to Weisbachj even when the current strikes obliquely upon 

 the plane J (see Figure 3) there exists a certain zone A in which the 

 resulting pressure is normal to the plane « In the case of a rock-fill, 

 as has been previously explained, the sprays B and C lose importancej 

 and the true intensity of pressure is reached solely in zone Ao 



Even if the Weisbach hypothesis is not acceptedj one need only ob- 

 serve Figure A, in which has been pictured the current vein produced 

 by the wave upon breaking , in order to understand that the wave strikes 

 with appreciabLe normality upon the usual slopes of rock-fill dikes o 



Some assume that the greatest velocity attained by the liquid 

 molecules of a breaking wave is equal to the sum of the wave velocity 

 and the maximum orbital velocity,, This belief cannot be proven, but 

 it is sufficient that the maximum orbital velocity, -vdiich is the 

 only molecular velocity existing, become equal to or somewhat exceed 

 the vrave velocity in order that the crest molecules of the wave fall 

 upon the anterior slope as a wave breaks o 



The maximum orbital horizontal velocity as the wave breaks is: 



where H is the water depth; h is "the serai-height of the wave or A/2| 

 L the semi-length of the wave| T the semi-period and 



As the wave breaks the orbital velocity must equal the wave velocity 



If TfK 



-rrhH U 





from which 



L = 7rhK 



