The total forces and moments are the sums of the dynamic and hydrostatic 

 components; therefore, as before, 



K^=\+% (7-110) 



and 



The pressures, forces, and moments computed by the above procedure will be 

 approximations, since the assumed wave behavior is simplified. Where 

 structures are located landward of the still-water line the preceding 

 equations will not be exact, since the runup criterion was assumed to be a 

 fixed fraction of the breaker height. However, the assumptions should result 

 in a high estimate of the forces and moments. 



*************** EXAMPLE PROBLEM 36*************** 



GIVEN ; The elevation at the toe of a vertical wall is 0.6 m (2 ft) above the 

 mean lower low water (MLLW) datum. Mean higher high water (MHHW) is 1.3 m 

 (4.3 ft) above MLLW, and the beach slope is 1:20. Breaker height is H, = 

 3.0 m (9.8 ft), and wave period is T = 6 s . 



FIND: 



(a) The total force and moment if the SWL is at MHHW; i.e., if the wall is 

 seaward of still-water line. 



(b) The total force and moment if the SWL is at MLLW; i.e., if the wall is 

 landward of still-water line. 



SOLUTION: 



(a) The breaking depth dj, can be found from Figure 7-2. Calculate, 



H 



b 3.0 



= = 0.0085 



2 2 

 gT 9.8 (6) 



and the beach slope, 



m = tan 3 = ^ = 0.05 

 r2 = 



Enter Figure 7-2 with It/gT'' = 0.0085 and, using the curve for m = 0.05 , 

 read 



^= 1.10 



7-196 



