72. The height of a wave transmitted by overtopping has been found to 

 be a function of incident wave height, period, freeboard (vertical distance 

 from the crest to the mean water level), slope, crest width, and surface char- 

 acteristics affecting runup. Water depth and bottom slope at the toe of the 

 structure also affect wave transmission by overtopping to the extent that they 

 affect the characteristics of the incident wave. The reflection characteris- 

 tics and permeability of the structure also have an effect. Figure 11 illus- 

 trates incident wave energy being partially reflected, partially dissipated in 

 turbulence at the seaward face, and partially dissipated by viscous effects. 

 Energy not reflected or dissipated in these ways either passes through or over 

 the breakwater, or both. The explicit method developed by Seelig (1980b) for 

 predicting wave heights transmitted by overtopping is as follows: 



\-ho(h) (26) 



where 



H^ = transmitted wave height 

 K^ = transmission coefficient (by overtopping) 



= c(l - I) (27) 



C = an empirical coefficient 



= 0.051 - 0.11 ^(for §- < 3.2\ (28) 



F = freeboard 



R = potential runup, as if the seaward slope were infinitely high 



B = crest width 



h = total height of the crest above the sea bottom 

 c ° 



ti. = incident wave height 



73. Runup can be estimated by a number of methods, but the method de- 

 veloped by Ahrens and McCartney (1975) is particularly useful for analysis by 

 the wave transmission formula above. It is expressed as ^ 



R - ^ (29) 



H " (1 ^ bU ^^' 



where a and b are empirical coefficients associated with the particular 

 type of armor unit in place. In this case, the surf similarity parameters c 

 (Equation 4) is related to the incident wave height, the equivalent deepwater 



46 



