8. Even in the limiting case of waves with a small 

 significant height incident for a very long time on 

 relatively large riprap, there will be a few rare waves high 

 enough to remove the smallest stones of the riprap pack 

 and hence give damage. 



9. The movement of the stone is greatest on the flatter 

 slopes although the net erosion is small. This movement 

 results in self-healing by the smaller stones. 



These conclusions offer a somewhat different view of damage development 

 than was accepted at that time based on regular wave experiments. The conclusion that 

 an equilibrium level of damage may not occur provided motivation to include damage in 

 a stability model. 



Using Thompson and Shuttler's riprap stability data. Van der Meer (1988) 

 stated that the damage rate should be linear up to 500 to 1,000 waves but "for large A^^^, 

 numbers a limit to the damage should be reached (equilibrium)." These criteria for the 

 relation between damage and the number of waves were limited to tests where damage 

 was larger than 5 = 3 after 5,000 waves and where the filter layer was not visible after 

 5,000 waves. Van der Meer's discussion of damage progression is limited to widely 

 graded armor, which may not deteriorate in a manner similar to uniformly sized stone 

 armor. This will be discussed further in the next chapter. 



3.4 Damage Progression Prediction 



Table 7-9 in the SPM (1984), included herein as Table 3.1, provides a 

 deterioration model for armor stability based on regular wave data from model studies 



44 



