M and M, , given above, are the total moments acting, when there is still 

 water of depth 3 meters (10 feet) on the leeward side of the structure. The 

 maximum moment at which there is wave action on the leeward side of the 

 structure will be M - M , with M and M evaluated for the appro- 

 priate wave conditions prevail on both sides of the structure. 



M = [0.44 - (-0.123)] (10)(3)-^ = 152.0 ^^^ (34,200 ^^^ ) (T = 6 s) 

 net m 



ft 



The combined moment due to both hydrostatic and wave loading is found using 

 equation (7-77). For this example, 



M 



10(3)- 



a total 



+ 118.8 = 163.8 ^^-^ (36,800 ^^^ ) 



m 



ft 



(T = 6 s) 



M 



t total 



^^(3^ + (-33.2) = 11.8 ^(2,650 i^) 



m 



ft 



Figures 7-93, 7-94, and 7-95 are used in a similar manner to determine 

 forces and moments on a structure which has a reflection coefficient of x = 

 0.9 . 



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



d. Wall of Low Height . It is often not economically feasible to design a 

 structure to provide a non-overtopping condition by the design wave. Con- 

 sequently, it is necessary to evaluate the force on a structure where the 

 crest of the design clapotis is above the top of the wall, as shown in Figure 

 7-96. When the overtopping is not too severe, the majority of the incident 

 wave will be reflected and the resulting pressure distribution is as shown in 

 Figure 7-96, with the pressure on the wall being the same as in the non- 

 overtopped case. This truncated distribution results in a force F' which is 

 proportional to F , the total force that would act against the wall if it 

 extended up to the crest of the clapotis (the force determined from Figures 7- 

 91 or 7-94). The relationship between F' and F is given by 



F' = 



r^l 



(7-78) 



where r^. is a force reduction factor given by 



and 



Y 



= - (2 - -) when 0.50 < - < 1.0 I 



r = 1.0 



when 



- 2 1.0 



y 



(7-79) 



where b and y are defined in Figure 7-96. The relationship between r-? 

 and b/y is shown in Figure 7-97. 



7-173 



