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* EXAMPLE PROBLEM 3************** 



GIVEN: A rubble-mound breakwater with concrete tetrapod armor units on 

 the structure trunk; dg = 20 feet (6,1 meters); cot 0=2; cot B = 20. 

 The structure is being designed for the maximum wave height at the toe 

 depth; the longest wave period expected is 11 seconds. From design 

 methods (see SPM, Ch. 7), the following are determined: breaker height, 

 H^, is 23,4 feet (7.1 meters) and H^ = 18,7 feet (5,7 meters). 



FIND: Wave runup on the breakwater trunk; assume the waves are approach- 

 ing normal to the structure. 



SOLUTION: The structure is a breakwater with concrete armor units; 

 therefore, the flow chart in Figure 4 is used, as follows: 



(a) From Appendix C, and assuming the tetrapods will be placed 

 randomly and in a two-unit armor-layer thickness, 



r = 0.45 , 



(b) From Stoa (1978b) , a value of R/H^ for a smooth slope is 

 .nding dg/H^ and 



d 



determined by first finding dg/H^ and H^/gT^, 



^ = _20_ ^ 1 07 



H' 18,7 • 



o 



\= ^-^ ^= 0,0048 . 



gT2 (32.2)(11)2 



From Figure 9 in CETA 78-2 (Stoa, 1978b), and without correcting for 

 smooth-slope scale effects, 



= 2.7 . 

 0/ smooth slope 



(c) Again, following Figure 4 of this report, the scale-effect 

 correction is 



k = 1.03 . 



(d) Runup on this rough slope is 



R = (U (H')(r)(k) 



\ o' smooth slope 



= (2.7) (18.7) (0.45) (1.03) 



R = 23.4 feet (7.13 meters) 

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