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



GIVEN : A design wave with H = 6 f t and T = 8 sec is incident on a 

 rubble structure with a cross section as shown in Figure 7-34, 

 situated in a depth dg = 10 ft. The crest of the structure is 

 b = 10 ft wide and is 1 ft above the SWL. 



FIND : 



(a) The height of the wave transmitted over the structure by over- 

 topping if the structure is permeable. 



(b) The reduction in transmitted wave height if an impermeable core 

 is included in the structure. 



SOLUTION : Calculate: h = dg + crest height above SWL = 10 + 1 = 11 feet, 

 then, 



b 10 



- = — = 0.909 , 



h 11 



d, 10 



11 



= 1.1 , 



gT2 (32.2) (8)2 

 '^s 10 



gT2 (32.2) (8)2 



= 0.0029 , 



= 0.0048 . 



For a permeable structure, find the corresponding Ht/H^ values for 

 b/h = 0.909 by interpolating between h/dg = 1.033 in Figure 7-36 

 and h/dg = 1.133 in Figure 7-37, and using the curve for H^/gT^ = 

 0.00269 and dg/gT^ = 0.00455 in Figure 7-36 and the curve for 

 %/gT^ = 0.00249 and dg/gT^ = 0.00414 in Figure 7-37. For h/dg = 

 1.033 from Figure 7-36, H^/H^ = 0.44 and for h/dg = 1.133 from 

 Figure 7-37, Ht/H-i = 0.31; therefore, 



- ^ 0.35 . 



Hence, 



H^ = (0.35) H. = 0.35(6) - 2.1 ft. 



7-62 



