PREDICTION Of IRREGULAR WAVE OVERTOPPING 



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John Ahrens 



I. INTRODUCTION 



This report gives a proposed technique for predicting the average 

 and peak overtopping rates caused by wind-generated waves acting on 

 coastal structures. No guidance for predicting the overtopping rates 

 for irregular wave conditions is currently available in the Shore Pro- 

 tection Manual (SPM] (U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, 1975]-'^, or other Corps publications. Therefore, this 

 interim guidance is provided until the results of the Coastal Engineering 

 Research Center (CERC) laboratory study of runup and overtopping by 

 irregular waves are available. 



The approach is consistent with, relies on, and extends the SPM 

 section on wave overtopping. In addition to the proposed technique, 

 the method provides a simple but plausible means of judging the con- 

 servatism or nonconservatism of the traditional approach to predicting 

 overtopping based on monochromatic wave conditions. In applying the 

 procedures described, a word of caution is noted: Some larger waves 

 in the spectrum may be depth- limited and break seaward of the structure. 

 In this case, the rate of overtopping may be overestimated. 



II. MONOCHROMATIC WAVE OVERTOPPING EQUATION 



Equation 7.6 in the SPM (Sec. 7.22) is given to compute wave over- 

 topping. Weggel (1976)^ provides the background information on how this 

 equation was developed and gives additional information on its use in 

 supplementing the discussion in SPM. The overtopping equation from the 

 SPM is written as 



in which 



1/2 



Q^ = (gQSH^^) e L « 



0.217 ^ / h-dg 



tanh" 



CD 



^U.S. ARMY, CORPS OF ENGINEERS, COASTAL ENGINEERING RESEARCH CENTER, 

 Shore Protection Manual , 2d ed. , Vols. I, II, and III, Stock No. 

 008-022-00077-1, U.S. Government Printing Office, Washington, D.C., 

 1975, 1,160 pp. 



^WEGGEL, J.R., "A Wave Overtopping Equation," Proceedings of the 15th 

 Conference on Coastal Engineering, 1976. 



