Therefore 



k' = 1 + 0.75 (0.3 + 0.1) 0.37 = 1.11 



and the corrected overtopping rate is 



Q^ = k' Q 



Q = 1.11 (0.47) = 0.5 m-^/s-m (5.4 ft^/s-ft) 



The total volume of water overtopping the structure is obtained by 

 multiplying Q by the length of the structure and by the duration of the 

 given wave conditions. 



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



b. Irregular Waves . As in the case of runup of irregular waves (see Sec. 

 II,l,b, Irregular Waves), little information is available to accurately 

 predict the average and extreme rate of overtopping caused by wind-generated 

 waves acting on coastal structures. Ahrens (1977b) suggests the following 

 interim approach until more definitive laboratory tests results are 

 available. The approach extends the procedures described in Section II, 2, a on 

 wave overtopping by regular (monochromatic) waves by applying the method 

 suggested by Ahrens (1977a) for determining runup of irregular waves. In 

 applying his procedure, note a word of caution: some larger waves in the 

 spectrum may he depth-limited and may break seaward of the structure, in which 

 case, the rate of overtopping way be overestimated. 



Irregular wave runup on coastal structures as discussed in Section II,l,b 

 is assumed to have a Rayleigh distribution, and the effect of this assumption 

 is applied to the regular (monochromatic) wave overtopping equation. This 

 equation is expressed as follows: 



Q=(sQ>;') 



1/2 



0.217 , ,-1 

 tanh 



h-d 



£ 



R 



(7-10) 



where 



h-d 



< 



< 1.0 



In applying this equation to irregular waves and the resulting runup and 

 overtopping, certain modifications are made and the following equation 

 results : 



in which 



%- 



g Q 



■o yo)i 



^ / h-d \ R 



(7-14) 



/h-d \ R 

 where Q is the overtopping rate associated with R , the wave runup with a 



7-58 



