is dissipated by bottom friction as the waves travel from deep water 

 to the structure site, the computed deepwater height should be increased 

 accordingly. See Section 3.7, HURRICANE WAVES, for a discussion of wave 

 height attenuation by bottom friction. 



Applying Equation 7-5 to the example problem gives: 



8.4 , ^^ ^ ^ 



H = = 8.3 ft . (T = 6 sec.) 



° (0.85) (1.19) 



A similar analysis for the 10-second wave gives. 



H^ = 8.3 ft . (T = 10 sec.) 



A wave advancing from the direction for which refraction was analyzed, 

 and with a height in deep water greater than the computed H^, will break 

 at a distance greater than Xp feet in front of the structure. Waves 

 with a deepwater height less than the Wq computed above could break 

 directly against the structure; however, the corresponding breaker height 

 will be less than the design breaker height determined from Figure 7-4. 



7.123 Nonbreaking Waves . Since statistical hindcast wave data are 

 normally available for deepwater conditions (d > Lo/2) or for depth 

 conditions some distance from the shore, refraction analysis is necessary 

 to determine wave characteristics at a nearshore site. (See Section 2.3, 

 WAVE REFRACTION.) Where the Continental Shelf is broad and shallow, as in 

 the Gulf of Mexico, it is advisable to allow for a large energy loss due to 

 bottom friction (Savage, 1953), (Bretschneider, 1954a, b). (See Section 

 3„7, HURRICANE WAVES.) 



General procedures for developing the height and direction of the 

 design wave by use of refraction diagrams follow: 



From the site, draw a set of refraction fans for the various waves 

 that might be expected (use wave period increments of no more than 2 

 seconds), and determine refraction coefficients by the method given in 

 Section 2.3, WAVE REFRACTION. Tabulate refraction coefficients determined 

 for the selected wave periods and for each deepwater direction of approach. 

 The statistical wave data from synoptic weather charts or other sources 

 may then be reviewed to determine if waves having directions and periods 

 with large refraction coefficients will occur frequently. 



The deepwater wave height, adjusted by refraction and shoaling 

 coefficients, that gives the highest significant wave height at the 

 structure would indicate direction of approach and period of the design 

 wave. The inshore height so determined is the design significant wave 

 height. A typical example of such an analysis is shown in Table 7-1. 



7-13 



