extended to include the effects of irregular breaking and nonbreaking waves and wave 

 period (Ahrens 1975, Ahrens and McCartney 1975, Carver and Wright 1991, SPM 

 1984), various armor layer types and armor gradation (e.g. SPM 1984), and number of 

 waves (Medina and McDougal 1988). 



Other regular- wave stability formulations that have been utilized in recent 

 years include Hedar (1960, 1986), Ahrens and McCartney (1975), and Losada and 

 Gimemenz-Curto (1979). Ahrens (1975), Ahrens and McCartney (1975), Losada and 

 Gimemenz-Curto (1979), and Pilarczyk and Den Boer (1983) all showed dependence of 

 wave period on stability number for regular waves. Each of these authors showed that 

 minimum stability occurred for surf similarity numbers or Iribairen numbers between 2 

 and 4, corresponding to plunging to collapsing breakers. The surf similarity number 

 was defined as ^ = tanB / {H/Lf^ where 6 = structure slope, H = regular wave height, 

 and L = local or deep water wave length. Thompson and Shuttler (1975) conducted an 

 extensive series of irregular-wave armor stability experiments. Their conclusions on 

 damage progression were insightful and are discussed in the next chapter. Using 

 Thompson and Shuttler' s data and data from his own experiments. Van der Meer (1988) 

 developed a stability model which explicitly included wave period, structure 

 permeability, storm duration and damage for a single design storm. The Hudson and 

 Van der Meer equations will be discussed further in the following chapters. The above 

 mentioned stability models predict minor damage reasonably well, although poor 

 predictions are common. Pfeiffer (1991) compared the models of Hudson (1958), 



