from tests of other concrete armor units. Note from the table that waves 

 producing greater than 10 percent damage to a dolos structure will produce 

 lesser damage levels to structures covered with other armor units. Concrete 

 units in general will fail more rapidly and catastrophically than quarrystone 

 armor. 



Caution must be exercised in using the values in Table 7-9 for breaking 

 wave conditions, structure heads, or structures other than breakwaters or 

 jetties. The damage zone is more concentrated around the still-water level on 

 the face of a revetment than on a breakwater (Ahrens, 1975), producing deeper 

 damage to the armor layer for a given volume of armor removed. As a result, 

 damage levels greater than 30 percent signify complete failure of a 

 revetment's armor. Model studies to determine behavior are recommended 

 whenever possible. 



The following example illustrates the ways in which Table 7-9 may be used. 



*************** EXAMPLE PROBLEM 38 ************** 



GIVEN ; A two-layer quarrystone breakwater designed for nonbreaking waves and 

 minor overtopping from a no-damage design wave ^d=o ~ ^'^ ™ (8.2 ft) 

 and K^ = 4.0 . 



FIND : 



(a) The wave heights which would cause 5 to 10 percent, 10 to 15 percent, 

 15 to 20 percent, and 20 to 30 percent damage. The return periods of these 

 different levels of damage and consequent repair costs could also be 

 estimated, given appropriate long-term wave statistics for the site. 



(b) The design wave height that should be used for calculating armor weight 

 if the breakwater is a temporary or minor structure and 5 to 10 percent 

 damage can be tolerated from 2.5-m waves striking it. 



(c) The damage to be expected if stone weighing 75 percent of the zero- 

 damage weight is available at substantially less cost or must be used in an 

 emergency for an expedient structure. 



SOLUTION : 



(a) From Table 7-9, for rough quarrystone; 



7-212 



