The term dJgT is calculated for each wave period for use in Figure 7-4 in 

 the SPM. 



where 



d, = depth of water at structure toe 

 g= acceleration because of gravity 

 T= wave period 



The corresponding Hi,/d, (where Hi, is the breaking wave height) is found by 

 interpolating between nearshore slopes 0.03 and 0.04 for Profile 255 "s nearshore 

 slope of 0.0357 ( 1 :28). Multiplying H,,/d, by water depth (from Table 5) gives 

 the depth-limited breaking wave height. This approach, rather than the common 

 dh = 1 .3///, criterion (where c//, is breaking depth), is preferred for structure design 

 because it accounts for nearshore slope and for the distance traveled between 

 initiation of breaking and wave impact. 



USAGE (1986) specifies use of//;,, (average of the highest 10 percent of all 

 waves) for design of rubble-mound structures. Depth-limited breaking wave 

 heights calculated as described above are representative of //„„„ and must be 

 converted to //;„ for calculation of stone size. For conversion, it is assumed that 

 the H,„ax calculated above is approximately equal to Hi (average of the highest 

 2 percent of all waves). On the assumption that wave height is described by a 

 Rayleigh distribution, this H; was converted to an //,,„^ and then to an //,„. 

 Table 6 lists the depth-limited breaking wave height (//,,), //,.,„>, and ///„ by period 

 and water level. Note that the largest Ht, occurs for 12.5-sec periods for all water 

 levels. 



Table 6 



Design Wave Heights 



Period 

 Sec 



10-Year Water Level 



50-Year Water Level 



100-Year Water Level 



ft 



Hnns 



ft 



ft 



ft 



H,„,s 

 ft 



ft 



H, 

 ft 



Hrms 

 ft 



Hio 

 ft 



3.5 



13.1 



5.93 



10.6 



14.3 



6.48 



11.5 



14.7 



6.68 



11.9 



4.5 



13.1 



5.93 



10.6 



14.3 



6.48 



11.5 



14.7 



6.68 



11.9 



5.5 



13.9 



6.33 



11.3 



14.3 



6.48 



11.5 



14.7 



6.68 



11.9 



6.5 



15.7 



7.12 



12.7 



16.5 



7.51 



13.4 



17.1 



7.75 



13.8 



7.5 



16.4 



7.43 



13.2 



17.9 



8.12 



14.5 



17.8 



8.11 



14.4 



8.5 



17.9 



8.15 



14.5 



18.6 



8.46 



15.1 



19.2 



8.73 



15.5 



9.5 



183 



8.30 



14.8 



19.6 



8.90 



15.8 



20.2 



9.18 



16.3 



10.5 



18.6 



8.46 



15.1 



20.3 



9.24 



164 



20.6 



9.35 



16.7 



11.5 



19.1 



8.70 



15.5 



20.9 



9.50 



16.9 



21.0 



9.53 



17.0 



12.5 



19.3 



8.78 



15.6 



20.9 



9.50 



16.9 



21.6 



9.80 



17.4 



Chapter 4 Structure Design 



43 



