SOLUTION : 



Computations are shown for the 6-second wave; only the final results 

 for the 10-second wave are given. 



From the given information, compute ds/gT^. 



Enter Figure 7-4 with the computed value of dg/gT^ and determine value 

 of H^/dg from the curve for a slope of m = 0.050. 



-—. = 0.0065 ; -— = 1.12 . (T = 6 sec.) 



Note that H^j/dg is not identical with H^j/dj, where d|j is the 

 depth at breaking and dg is the depth at the structure. In general, 

 because of nearshore slope, dg < d^; therefore H^^/dg > H^^/d^j. 



For the example, breaker height can now be computed from, 



Hj, = 1-12 d^ = 1.12(7.5) = 8.40 ft . (T = 6 sec.) 



For the 10-second wave a similar analysis gives, 



Hj, = 1.30 d^ = 1.30(7.5) - 9.75 ft . (T = 10 sec.) 



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 dg/gT^ = o'^ 

 (infinite period). For the example problem, 



d^ Hj, 



—z =0 ; —- ^ 1.41 (m = 0.050) , 

 gT ^s 



Hj, = 1.41 d^ = 1.41 (7.5) = 10.6 ft . 



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



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

 with the design breaker 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 Section 2.3, 

 WAVE REFRACTION.) Figure 7-5 is based on observations by Iversen 

 (1952a, 1952b), as modified by Goda (1970), of periodic waves breaking on 

 impermeable, smooth, uniform laboratory slopes. Figure 7-5 is a modified 

 form of Figure 7-3. 



7-10 



