Plunging (breaking) waves 



JL— = 6.2 P° 18 



( S 



\02 



\-0-5 



(21) 



Surging (nonbreaking) waves 



= 1.0 p-™(J-V Vc5Te£ (22) 



A ArfO ^ 



where £ z is the surf similarity parameter, 

 tan 6 



271 H (23) 



82 



A = relative mass density of stone, = p a /p w - 1 (24) 



p a = mass density of armor 



p w = mass density of water 



D^q = nominal diameter of stone, = (W 50 /pJ' /i (25) 



W 50 = 50 percent value (median) of the mass distribution curve 



P = permeability coefficient of the structure as defined by Van der 



Meer (1987) (Figure 47) 

 S = damage level, = A e I D^q 2 (26) 



A e = eroded cross-sectional area in profile 

 N = number of waves (storm duration) 



| z = surf similarity parameter 



T z = average wave period 



The term on the left side of Equations 21 and 22 is referred to as the 

 stability number A^ as defined by Van der Meer. 



N. = — ^- (27) 



Van der Meer's equations clearly include more explicit dependence on 

 important parameters of the problem than Hudson's formula. They are 

 formulated in terms of irregular wave parameters. A dependence on wave 

 period comes in through the surf similarity parameter, £ r Permeability, 

 which has been shown to impact stability, is also included as well as damage 

 level and storm duration. However, there are some important explanations 

 and qualifications which need to be considered when applying Van der Meer's 

 equations. Van der Meer's definitions of significant wave height, 

 permeability, and acceptable damage levels must be used when applying the 

 equations. Also, design conditions must fall within the acceptable ranges of 

 structure slope, wave steepness, storm duration, and mass density. Both the 

 Hudson formula and Van der Meer's equations are suitable in stability analysis 



Chapter 4 Structural Design Guidance 



