The height of the free surface above the bottom y, when the wave crest 

 and trough are at the structure, may be determined from Equations 7-66 

 and 7-67, 



Yc 



and 



Yt 



= d + h„ + I ^-^ 1 H, 

 d + h„ - |i^ 1 H. 



y^ = 10 + 3.50 + (1) (5) - 18.5 ft., 



y^ = 10 + 3.50 - (1) (5) = 8.5 ft. 



A similar analysis for the 10-second wave gives 

 y^ = 19.5 ft. , 



y, = 9.5 ft. 



(T = 6 sec.) 



(T = 10 sec.) 



The wall would have to be about 20 feet high if it were not to be over- 

 topped by a 5-foot high wave having a period of 10 seconds. 



The horizontal wave forces may be evaluated using Figure 7-66. 

 Entering the figure with the computed value of H^/gT^, the value of 

 F/wd^ can be determined from either of two curves of constant H.^/d. 

 The upper family of curves (above F/wd^ = 0,5) will give the dimension- 

 less force when the crest is at the wall, F^^/wd^; the lower family of 

 curves (below F/wd^ = 0.5) will give the dimensionless force when the 

 trough is at the wall, F^/wd^. For the example problem, with H^/gT^ = 

 0.0043, and H^/d = 0.50, 



-— = 1.25: -—7 = 0.29. (T = 6 sec.) 



wd wd 



Therefore, assuming a weight per unit volume of 64.0 lbs. /ft. for sea 

 water, 



F^ = 1.25 (64) (10)2 = 8,000 Ibs./ft., 



(T = 6 sec.) 

 F^ = 0.29 (64) (10)2 ^ J 86Q Jbs./ft. 



The horizontal line in Figure 7-66 (F/wd^ = 0.5) represents the hori- 

 zontal hydrostatic force against a wall in still water of depth, d. 

 For the example problem, if the water depth on the leeward side of the 

 wall is also 10 feet and there is no wave action, the maximum seaward 

 acting horizontal force will be F^ = 0.5 wd^. Therefore, the net 

 horizontal force will be, 



F„,t = 1-25 (64) (10)2 _ 0.5 (64) (10)2, 



F 



7-137 



