the model scale is large enough to ensure that the motion is fully tur- 

 bulent in the model. For most harbor model studies, the linear scales 

 are relatively small and the scale effects in wave reflection and trans- 

 mission are appreciable. Le Mehaute (1965) stated that scale effects 

 for both wave reflection and transmission can be reduced by using model 

 quarrystone sizes in the protective cover layers and the core material 

 larger than those determined by the linear scale of the model; i.e.. 





D =^!f (4-32) 



where D is the effective stone diameter, Lj^/Lp the linear scale, and 

 K a coefficient greater than one. The value of^ K for the armor units 

 in the protective cover layer, the characteristics of which determine the 

 reflection coefficient for a rubble breakwater or wave absorber with a 

 given slope, is not the same as the value of K for the core material, 

 which determines to a large extent the wave transmission characteristics 

 of the breakwater. This is especially true if the crest of the core 

 material section is high relative to the total height of the structure. 

 The values of K, for both wave reflection and wave transmission through 

 the voids of the breakwater or wave absorber, can best be determined by 

 experiment. Approximate values of K for wave transmission can be ob- 

 tained from a nomograph by Le Mehaute (1965) based on analytical con- 

 siderations and available experimental data (Fig. 4-5). The variables 

 of this nomograph are defined as follows: 



AH/AL is the gradient of the head loss through the voids in 

 the core material part of the breakwater section. AH is the 

 height of the incident wave, H^^, and AL the average width of 

 the core material section. Dp is the effective quarrystone di- 

 ameter of the prototype core material in centimeters, and is 

 taken to be the 10 percent smaller than quarrystone from the core 

 material gradation curve. P is the porosity of the core material 

 (0 < P < 1). 



Le Mehaute (1965) assumes that the gradation curves of the core material 

 in model and prototype are the same, or Pm = Pp. The use of the nomo- 

 graph to estimate the size of model core material necessary to minimize 

 the scale effects in wave transmission through the voids of a breakwater 

 core (scale effects are assumed to be negligible insofar as transmission 

 through the outer armor-unit cover layers are concerned) is given in the 

 following example. 



Given: 





= 



AH - 15 



ft, 







AL 



= 



50 ft, 











= 



1 

 100' 









Dp 



- 



0.50 ft = 



15.2 



cm. 



and 



Pp 



= 



0.35. 









223 



