breaker height depends, therefore, on critical design depth at the structure 

 toe, slope on which the 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: 



d 

 H = — § (7-5) 



where d is depth at the structure toe, B is the ratio of breaking depth 

 to breaker height di^/Hi , m is the nearshore slope, and t is the 

 dimensionless plunge distance ^ /H, from equation (7-4). P 



The magnitude of g to be used in equation (7-5) cannot be directly known 

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

 from equations (7-4) and (7-5) using g 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 2************** 

 GIVEN: 



(a) Design depth structure toe, d = 2.5 m (8.2 ft) 



(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 s (minimum) 



T = 10 s (maximum) 



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

 minimum wave periods. 



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 



d „ . 

 ® - = 0.0071 (T = 6 s) 



gX^ (9.8) (6)^ 



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

 of IV /d~ from the curve for a slope of m = 0.050 



% . ..., ^ 



= 0.0071 ; -/- = 1.10 (T = 6 s) 



, 



gT 6 



7-9 



