When vertical-wall breakwaters of the type discussed above are situ- 

 ated where the bottom slopes seaward and in depths only slightly greater 

 than the wave heights, the waves are no longer completely reflected but 

 are partially destroyed orbitally and can break on the structure with re- 

 sulting shock pressures that are much higher in intensity and much shorter 

 in duration than those caused by the clapotis-type of wave motion. In 

 this case the phenomena are so complex that an adequate analytical solu- 

 tion has not been possible, and it is necessary to rely on scale-model 

 tests. The magnitude of shock pressures formed by breaking waves varies 

 greatly with the form of the waves as they make contact with the break- 

 water. The following factors are of primary importance in determining 

 the magnitude, duration, and disposition of the pressures formed by 

 breaking waves on impervious breakwater surfaces: 



(a) The wave dimensions, angle of wave approach, water depth 

 at the toe of the structure, the bottom slope seaward, and the 

 reflective characteristics of the structure determine the wave- 

 form when contact is made with the structure face. 



(b) The concentration of entrained air in the water as the 

 wave impinges on the structure face and the pressures in the 

 bubbles of entrained air. 



(c) The pressures in air pockets that may be trapped between 

 the structure face and the wave front when contact is made with 

 the structure face. 



(d) The pressures in air cushions formed by wave fronts and 

 the wall to allow the escape of air upward or laterally. 



Thus, flow phenomena can be assumed a function of 



d = depth of water in which the structure is situated, 

 measured at the seaside toe 



E^,, = modulus of elasticity of the water 



e/ = bulk modulus of the breakwater material 



g = acceleration due to gravity 



H = height of wave that breaks on the structure 



k = adiabatic constant of air 



p = pressure intensity on the vertical wall 



p^^ = atmospheric pressure 



T = wave period 



3 = angle of incident wave attack 



32 



