increments) of overtopping rates at each reach for each event simulated. 



65. A check was made to limit the calculated overtopping rates. As- 

 suming that the maximum volume that can overtop a wall (when the freeboard is 

 reduced to zero) is the volume contained between the elevation of the top of 

 the wall and the surface of the wave (Weggel 1976), and assuming linear wave 

 theory with a sinusoidal wave profile, Equation 9 can be derived. The 0.85 

 factor is included to account for nonlinearity of the real wave form. The 

 condition where Q reached its maximum rate was not common, occurring only at 

 the peak of the most severe events at existing reach D are expressed as 



(9) 

 _ 0.85 HL 

 max " 2irT 



66. The contribution from wind-aided overtopping was added to the rates 

 calculated from the physical modeling results. This contribution is calcu- 

 lated using Equation 10 (adapted from the SPM (1984, p. 7-44)). Equation 10 

 is multiplied by 0.30 to account for overprediction.* For wind speeds of 



60 mph or greater, W = 2.0 ; for wind speeds equal to 30 mph, W = 0.5. When 

 the wind speed is zero, W = 0.0 . For all other wind speeds W is inter- 

 polated from these values. Since wave runup data were not available from the 

 physical modeling, Equation 11 (Ahrens and McCartney 1975) was used to esti- 

 mate R in Equation 10. Equation 12 shows how the correction for wind aided 

 overtopping is combined with the physical modeling results to produce total 

 overtopping Q t . Wind aided overtopping was usually less than 10 percent of 

 total overtopping. These equations are written as follows: 



(10) 



S-°..) 



C =0.3W(d + 0.1J cos a cos 8 



where 



C = fraction of overtopping which is wind aided 

 W = coefficient based upon wind speed 

 R = wave runup, ft 



a = wind angle relative to line normal to structure, degrees 

 6 = structure slope, degrees 



* Personal communication with John Ahrens, 1985, Wave Research Branch, Wave 

 Dynamics Division, CERC. 



56 



