where 



C^ = overtopping rate (volume per unit time) per unit structure 

 length 



g = gravitation acceleration 



H^ = equivalent deepwater wave height 



h = height o£ the structure crest above the bottom 



dg = water depth at the structure toe 



R = runup on the structure that would occur if the structure 



were high enough to prevent overtopping (corrected for scale 

 effects, SPM Sec. 7.21) 



a,Qg = empirically determined coefficients that depend on incident 

 wave characteristics and structure geometry 



The SPM (Sec. 7.22) gives values of a and Q^ for a wide range of 

 structure types and wave conditions. 



Equation (1) provides an unusually good fit to observed overtopping 

 rates from laboratory tests using monochromatic waves (waves of constant 

 height and period). Q^ was used in equation (1) rather than Q to 

 specify overtopping by monochromatic waves. The following section in- 

 cludes some modifications to equation (1) to adapt it to irregular wave 

 conditions so that overtopping rates for irregular waves can be calculated 

 and compared to overtopping rates for monochromatic waves. 



III. ADAPTION OF MONOCHROMATIC WAVE OVERTOPPING EQUATION 

 TO IRREGULAR WAVE CONDITIONS 



The fundamental assumption in adapting equation (1) to irregular 

 wave conditions is that the runup caused by these conditions has a 

 Rayleigh distribution of the type commonly associated with wave heights. 

 This assumption was made by Ahrens (1977)^ to predict irregular wave 

 runup and appears reasonable but possibly somewhat conservative; i.e., 

 it will probably yield higher extreme values of runup than are actually 

 observed. The procedure for combining the assumption of a Rayleigh 

 distribution of wave runup with equation (1) for monochromatic wave over- 

 topping is outlined below. 



1. The Rayleigh runup distribution is given by 



Rp /ln(l/p)^''' 



= H (2) 



^AHRENS, J. P., "Prediction of Irregular Wave Runup," CETA 77-2, 

 U.S. Army, Corps of Engineers, Coastal Engineering Research Center, 

 Fort Belvoir, Va. , July 1977. 



