(b) Partially break with a poorly defined jet. 



(c) Establish an oscillatory motion of the water particles up or down 

 the structure slope, similar to the motion of a clapotis at a vertical 

 wall. 



The design wave height for a flexible rubble structure should usually be 

 the average of the highest 10 percent of all waves, H.„ as discussed in 

 Section 1,2. Damage from waves higher than the design wave height is 

 progressive, but the displacement of several individual armor units will not 

 necessarily result in the complete loss of protection. A logic diagram for 

 the evaluation of the marine environment presented in Figure 7-6 summarizes 

 the factors involved in selecting the design water depth and wave conditions 

 to be used in the analysis of a rubble structure. The most severe wave 

 condition for design of any part of a rubble-mound structure is usually the 

 combination of predicted water depth and extreme incident wave height and 

 period that produces waves which would break, directly on the part of interest. 



If a structure with two opposing slopes, such as a breakwater or jetty, 

 will not be overtopped, a different design wave condition may be required for 

 each side. The wave action directly striking one side of a structure, such as 

 the harbor side of a breakwater, may be much less severe than that striking 

 the other side. If the structure is porous enough to allow waves to pass 

 through it, more armor units may be dislodged from the sheltered side's armor 

 layer by waves traveling through the structure than by waves striking the 

 layer directly. In such a case, the design wave for the sheltered side might 

 be the same as for the exposed side, but no dependable analytical method is 

 known for choosing such a design wave condition or for calculating a stable 

 armor weight for it. Leeside armor sizes have been investigated in model 

 tests by Markle (1982). 



If a breakwater is designed to be overtopped, or if the designer is not 

 sure that it will not be overtopped the crest and perhaps, the leeward side 

 must be designed for breaking wave impact. Lording and Scott (1971) tested an 

 overtopped rubble-mound structure that was subjected to breaking waves in 

 water levels up to the crest elevation. Maximum damage to the leeside armor 

 units occurred with the still-water level slightly below the crest and with 

 waves breaking as close as two breaker heights from the toe of the 

 structure. This would imply that waves were breaking over the structure and 

 directly on the lee slope rather than on the seaward slope. 



7-203 



