



REDUCTION FACTOR = 1/(1-25 - 4.8Rp) 





sop = 0.04 



sop - 0.03 



sop = 0.02 



sop = 0.01 



sop = 0.005 



1.1 - 









Q 













tK 













< 



Q 



O 



1 - 

 .9 - 













■-'""' 



O 



g 

 u 



8 - 

 .7 - 





^'^ 









-.5 .5 1 



1.5 



_ 





RELATIVE CREST HEIGHT Rc/Hs 







Figure 49. Design graph with reduction factor for the stone diameter of a 

 tow-crested structure as a function of relative crest height and 

 wave steepness (Van der Meer 1991) 



20 



30 



100 110 120 



DISTANCE ALONG CHANNEL, CM 



Figure 50. Typical reef profile, as built, and after adjustment to severe 

 wave conditions (Ahrens 1987) 



The analyses on stability of reef breakwaters by Ahrens (1987,1989) and 

 Van der Meer (1990) concentrated on change in crest height due to wave 

 attack. Ahrens defined a number of dimensionless parameters used in 

 describing behavior of the structure. The main parameter is the crest height 

 reduction factor hjk c ', which is the ratio of the crest height at the end of the 

 laboratory test h c to the initial crest height h c '. 



86 



Chapter 4 Structural Design Guidance 



