corresponding to a given percent damage can then be calculated relative to the 

 design wave and stone. 



H,_{W,^ ^3^ 



H: W 



Figure 38 shows the percent damage potential for a range of armor weights 

 versus breaking wave height. A separate family of curves is provided for each 

 water level. These curves relate the damage potential of a particular stone size to 

 water-level recurrence interval. This approach can also be expanded to estimate 

 annual repair costs given a wave-height recurrence interval and stone- 

 replacement cost. 



Figure 39 shows the percent damage potential for a range of armor weights 

 versus non-breaking wave height for three wave directions. Breaking and non- 

 breaking stone size can be compared by examining the zero-percent damage 

 curves in Figures 38 and 39. 



It should be noted that the percent damage relationships from SPM (1984) 

 were intended for situations with nonbreaking waves incident on a structure 

 trunk. Therefore, caution is recommended where applying them in breaking 

 waves incident on structure heads and for stone revetments. 



Specification of armor weights to protect against zero damage is not practi- 

 cal. The designer must balance cost and availability of stone with potential 

 damage in selecting the most appropriate armor unit stone size. The New York 

 District has considerable experience in groin design for both the New Jersey and 

 Long Island, New York, coasts. At Westhampton Beach on Long Island, the 

 New York District specified armor unit weights of 10 to 14 tons for modification 

 of the existing groin field. Existing structures at Monmouth Beach have armor 

 weights of 4 to 10 tons. Although it is difficult to determine the extent to which 

 these structures have been damaged, in light of the stone-sizing analysis and the 

 greater depths at the Groin 44 extension, existing stone sizes at Monmouth Beach 

 are likely smaller than should be used for the extension. 



An annor weight (fF,„) of 12 tons with a grade range of 10 to 14 tons is 

 considered to be most appropriate for the Groin 44 extension. The most com- 

 monly occurring wave periods at the Long Branch wave gauge are 8.5 to 9.5 sec, 

 which correspond to depth-limited breaking wave heights of 18, 19, and 19.5 ft 

 for the 10-. 50-, and 100-year water levels, respectively. From Figure 38, one 

 can see that for these water levels with an eroded profile, a structure annored 

 with 12-ton stone will be susceptible to approximately 10, 15, and 20 percent 

 damage, respectively. Twelve-ton stone is larger than the zero-damage stone size 

 for any of the nonbreaking wave conditions. 



46 Chapter 4 Structure Design 



