The methods of Le Mehaute (1965) and Keulegan (1973) for the deter- 

 mination of K are compared in Table 4-3. The experiments by Keulegan 

 were conducted using stones of nearly equal diameter with a porosity of 

 0.46. Thus, for ease of calculation, the comparison was made using a 

 porosity of 0.46 for both the model and prototype core material. A more 

 reasonable value for P for quarry-run core material is about 0.35 to 

 0.40, depending on the gradation. The linear scale of the model, used 

 in the comparison, was 1:100, and the viscosity was 1.059 x 10"^, cor- 

 responding to a temperature of 21° Celsius (70° Fahrenheit). The water 

 depths, wave dimensions, and quarrystone sizes used represent the ranges 

 of these variables commonly found in prototype structures. Keulegan 's 

 equations and Table 4-3 show that the porosity and size of the core ma- 

 terial quarrystone have an appreciable effect on the wave transmission 

 coefficient (Hj^/H^i-) . Thus, it is important that accurate values of these 

 variables are obtained for the core material ixsed in the prototype struc- 

 tures. Keulegan 's equations also show that adjustments can be made in 

 both the ratios Pjn/Pp and Dji,/Dp to obtain practical solutions to the 

 problem of minimizing scale effects in wave transmission through rubble- 

 mound breakwaters. Generally, the problems of obtaining dynamic similar- 

 ity for wave transmission through rubble-mound breakwaters should be the 

 subject of future analysis and experimentation. However, until the re- 

 sults of these studies become available, such scale effects are consid- 

 ered to be reduced appreciably by Le Mehaute 's nomograph and Keulegan 's 

 equations, and by the proper selection of linear scale. The most accu- 

 rate of the two methods is unknown; however, it is presently recommended 

 that the value of K used in the model design should be the average of 

 the values obtained by the two methods, or 



K = 



^L ^^K 



(4-40) 



Table 4-3. Values of K according to Le Mehaute (1965) and Keulegan (1973) for 

 undistorted-scale models, L_ = 1:100. 



'^P 



Tp 



H 



^P 



K,' 



Kk 



Kl 



(ft) 



(s) 



(ft) 



(ft) 







Kk 



15 



5 



7.5 



0.25 



6.0 



4.6 



1.30 



15 



5 



7.5 



0.75 



3.5 



2.7 



1.30 



15 



10 



7.5 



0.25 



6.0 



4.2 



1.43 



15 



10 



7.5 



0.75 



3.5 



2.5 



1.40 



30 



10 



15.0 



0.25 



5.5 



4.0 



1.38 



30 



10 



15.0 



0.75 



3.0 



2.3 



1.31 



30 



15 



15.0 



0.25 



5.5 



3.9 



1.41 



30 



15 



15.0 



0.75 



3.0 



2.3 



1.31 



45 



15 



25.0 



0.25 



5.0 



3.7 



1.35 



45 



15 



25.0 



0.75 



2.7 



2.2 



1.23 



45 



20 



25.0 



0.25 



5.0 



3.6 



1.39 



45 



20 



25.0 



0.75 







2.7 



2.2 



1.23 



' SubscrijJts L and K refer to Le Mehaute and Keulegan, respectively. 



227 



