which is about 4Q percent greater than the monochromatic rate. The 

 wind effect on overtopping shown in the SPM example is not discus^sed 

 here, but it can be assumed that it would increase the irregular over- 

 topping by the same percentage (11 percent) as the monochromatic over- 

 topping. 



IV. GENERALIZING THE IRREGULAR WAVE OVERTOPPING TECHNIQUE 



Example 1 used a specific value of freeboard for the structure 

 (i.e., h - dg = 5 feet); however, the problem could have been worked 

 for any value of freeboard from to 17 feet, which is equivalent to 

 0.0 <_ (h - dg)/Rg < 1.0. The example can be considered in a more gen- 

 eral way by plotting the ratio of the average irregular wave overtopping 

 rate, Qp, to the monochromatic overtopping rate, Q^, as a function of 

 the relative freeboard (see Fig. 1). The ratio of the peak to monocPiro- 

 matic overtopping rates, Qo.5/Qm> ^^ also shown in Figure 1. When the 

 ratio of overtopping rates is used as in Figure 1, the influence of Q^ 

 cancels out and the curves are functions only of a and the relative 

 freeboard. Figure 1 shows the curves for a = 0.08, as given in Example 1, 

 and by reading the values off the curves for a relative freeboard of 

 0.294 the results of the example can be verified. 



Figure 2 shows a family of curves of %/% and Qq ^/Q^ for 

 a = 0.04, 0.06, 0.08, and 0.10 and demonstrates how a controls the shape 

 of the curves. This range of a's includes most of the a's tabulated in 

 the SPM (Sec. 7.22). Figure 2 also shows that generally Q^ is signifi- 

 cantly larger than Q^, for the range of a's presented. The irregular 

 wave overtopping characteristics shown in Figure 2 are consistent with 

 the trends observed by Tsuruta and Goda (1968)^ in laboratory tests with 

 both monochromatic and irregular waves. 



Figure 2 can be used to compute Q^, for various values of a and 

 (h - dg)/R3 by regarding the ratio Qj^/Q^ as a "correction" factor for 

 Q^ as illustrated in Example 2. Since it is relatively difficult to 

 read the values from Figure 2, the ratios of Qj^/Q^ and Qq ^/Qm are 

 given as a function of a and (h - ds)/Rs in tabular form in Tables 1 

 and 2, respectively. 



************** EXAMPLE PROBLEM 9************** 



To illustrate the use of the generalization presented, reconsider 

 Example 1, except assume the freeboard is 8 feet rather than 5 feet; 

 therefore, (h - dg)/Rg = 0.471. Using equation (1) for 



a = 0.08 

 Q^ = 0.035 



^TSURUTA, S., and GODA, Y., "Expected Discharge of Irregular Wave 

 Overtopping," Proceedings of the 11th. Conference on Coastal Engineering, 

 1968, pp. 833-852. 



