E = [6.2p0^'v/tii^]' 



(6.8) 



where Q = (P + 0.5)' and P = permeability coefficient varying in the range 0. 1 - 0.6. 

 Keep in mind that in Equation 6.8 is the structure slope measured from horizontal. 

 Later in this chapter, this requirement will be abandoned. Using Equations 3.7 and 6.8, 

 the minimum stability number can be expressed as 



N^ = C/, 6.2^2 P2(0'«^-°°">(cote)°-25e 



( s \0-2 



'N 



(6.9) 



where 



A'^ = HJAD„^Q = stability number based on the significant wave height 



C;v = empirical coefficient introduced here 



A^,^, = number of waves associated with the damage 5 starting from zero 

 damage 



For depth-limited breaking waves on a sloping beach in front of the 

 structure. Van der Meer (1988) proposed the use of ^2% ^"^d rewrote his equation for 

 relatively deep water using H2% = lAH^ based on the Rayleigh distribution of wave 

 heights where ^„ based on H^ was not changed. Note that the values of //j^ were not 

 tabulated in his report, so it is difficult to evaluate this shallow-water extension of his 

 stability equations. In the present experiment, incident irregular wave breakers were 

 spilling and plunging on the 1:20 beach slope and collapsing and surging on the 1:2 

 structure slope. However, plunging waves on the beach were also observed to hit the 



120 



