Where wave characteristics are not significantly modified by the 

 presence of structures, incident waves generally will break when the 

 depth is slightly greater than (^'^B^min' ^^ wave-reflection effects of 

 shore structures begin to influence breaking, depth of breaking increases, 

 and the region of breaking moves farther seaward. As illustrated by the 

 example, a structure sited on a 1 on 20 slope under action of the given 

 incident wave (H^ = 5.0 feet, T = 10 seconds) could be subjected to 

 waves breaking directly on it, if the depth at the structure toe were 

 between (d^)^^ =7.7 feet and id]y)^fj^^ = 12.5 feet. 

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



7.122 Design Breaker Height . When designing for a breaking wave condition, 

 it is desirable to determine the maximum breaker height to which the 

 structure might reasonably be subjected. The design breaker height H^p 

 depends on the depth of water some distance seaward from the structure 

 toe where the wave first begins to break. This depth varies with tidal 

 stage. The design breaker height depends, therefore, on critical design 

 depth at the structure toe, slope on which structure is built, incident 

 wave steepness, and distance traveled by the wave during breaking. 



Assuming that the design wave is one that plunges on the structure, 

 design breaker height may be determined from: 



"^ %-^ • "-^' 



where dg is depth at the structure toe; 3 is the ratio of breaking 

 depth to breaker height d2j/H25; m is the nearshore slope, and r^ is 

 the dimensionless plunge distance Xp/H^ from Equation 7-3. 



The magnitude of 3 to be used in Equation 7-4 cannot be directly 

 evaluated since it depends on breaking wave steepness that cannot be known 

 until Hjy is .evaluated. To aid in finding H^, Figure 7-4 has been 

 derived from Equations 7-3 and 7-4 using 3 values from Figure 7-2. If 

 maximum design depth at the structure and incident wave period are known, 

 design breaker height can be obtained using Figure 7-4. 



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



EXAMPLE PROBLEM *************** 



GIVEN: 



(a) Design depth structure toe, dg = 7.5 feet. 



(b) Slope in front of structure is 1 on 20, or m = 0.050. 



(c) Range of wave periods to be considered in design 



T = 6 sec (minimum) 

 T = 10 sec (maximum) 



FIND : Maximum breaker height against the structure for the maximum and 

 minimiom wave periods. 



7-8 



