Note that Hr/d Is not identical with H,/d where d is the depth at 



breaking and d is the depth at the structure. In general, because of 



nearshore slope, d < d, : therefore H,/d > H, /d, 



so' b s b b 



For the example, breaker height can now be computed from 



H, = 1.10 d = 1.10 (2.5) = 2.8 m (9.2 ft) (T = 6 s) 

 b s 



For the 10-second wave, a similar analysis gives 



H = 1.27 d = 1.27 (2.5) = 3.2 m (10.5 ft) (T = 10 s) 

 b 8 



As illustrated by the example problem, longer period waves result in higher 

 design breakers; therefore, the greatest breaker height which could possibly 

 occur against a structure for a given design depth and nearshore slope is 

 found by entering Figure 7-4 with d /gT = (infinite period). For the 

 example problem 



-^ = ; ^ = 1.41 (m = 0.050) 

 gT 8 



H = 1.41 d = 1.41 (2.5) = 3.5 m (11.6 ft) 

 b s 



*************************************** 



It is often of interest to know the deepwater wave height associated with 

 the design height obtained from Figure 7-4. Comparison of the design 

 associated deepwater wave height determined from Figure 7-4 with actual 

 deepwater wave statistics characteristic of the site will give some indication 

 of how often the structure could be subjected to breakers as high as the 

 design breaker. Deepwater height may be found in Figure 7-5 and information 

 obtained by a refraction analysis (see Ch. 2, Sec. HI, WAVE REFRACTION). 

 Figure 7-5 is based on observations by Iversen (1952a, 1952b), as modified by 

 Goda (1970a), of periodic waves breaking on impermeable, smooth, uniform 

 laboratory slopes. Figure 7-5 is a modified form of Figure 7-3. 



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

 GIVEN : 



(a) IL = 2.8 m (9.2 ft) (T = 6 s) 

 and 



IL = 3.2 m (10.5 ft) (see previous example) (T = 10 s) 



(b) Assume that refraction analysis of the structure site gives 





-p , K --85 (T = 6 s) 



7-11 



