particular probability of exceedance, P , and R is the wave runup of the 

 equivalent deepwater significant wave height, (K3J 



The term h-d„/R„ 

 s s 



will be referred to as the relative freeboard. The relationship between 

 Rp , Kg , and P is given by 



Rs 



LnP 



a/2 



(7-9) 



Equation (7-14) provides the rate of overtopping for a particular wave height. 



In analyzing the rate of overtopping of a structure subjected to irregular 

 waves and the capacity for handling the overtopping water, it is generally 

 more important to determine the extreme (low probability) rate (e.g., Qq QQ5) 

 and the average rate Q of overtopping based on a specified design storm 

 wave condition. The extreme rate, assumed to have a probability P of 0.5 

 percent or 0.005, can be determined by using equation (7-14). The upper group 

 of curves in Figure 7-35 illustrates the relation between the relative free- 

 board, [h-dgj/Rg , and the relative rate of overtopping, Q„ onc/Q > in terms 



of the empirically determined coefficient, a , where Q _is the overtopping 

 rate for the significant wave height. The average rate Q is determined by 

 first calculating the overtopping rate for all waves in the distribution using 

 equation (7-14). For example, in Figure 7-35, this has been calculated for 

 199 values of probabilities of exceedance at intervals of P = 0.005 (i.e., 

 P = 0.005 , 0.010 , 0.015 , ..., 0.995). Noting that Rp/Rg is a function of 



P , solutions will only exist for the previously stated condition that 



/h-ds\ Rg 

 < -T^ — r— < 1.0 



*-s 



Rp 



and Qp = for other values of P . The average of these overtopping rates 



is then determined by dividing the summation of the rates by 199 (i.e., the 

 total number of overtopping rates) to obtain Q . The lower group of curves 

 in Figure 7-35 illustrates the relation between the relative freeboard and the 

 relative average rate of overtopping Q/Q in terms of the empirically 

 determined coefficient a . 



**************** EXAMPLE PROBLEM 8************** 



GIVEN ; An impermeable structure with a smooth slope of 1 on 2.5 is subjected 

 to waves having a deepwater significant wave height H^ = 1.5 m (4.9 ft) 

 and a period T = 8 s . The depth at the structure toe is dg = 3.0 m (9.8 

 ft) ; crest elevation is 1.5 m (4.9 ft) above SWL (h-dg = 1.5 m (4.9 

 ft)) . Onshore winds of 35 knots are assumed. 



FIND ; 



(a) Estimate the overtopping rate for the given significant wave. 



(b) Estimate the extreme overtopping rate Qq qqc . 



(c) Estimate the average overtopping rate Q . 



7-59 



