where n^^g is the average root -me an -square (rms) water level from the three 

 seaward gages. The mean wave height, H, is defined as 



H = 0.625 H, 



2.5 n. 



y 1 + K 



C8D 



The wave period used to describe irregular wave conditions is the period 

 of peak energy density, Tp. The spectral-peakedness parameter, Qp (Goda, 

 1970), is used to characterize the spectral width for irregular wave conditions. 



36 

 Z 



1 J = l 



Z f J aj 



Af 



(,?; '^1 



(9) 



where j is the band number (11 spectral lines are used to make each band), 

 fj the frequency midpoint of the band, and Af the bandwidth frequency. a.j 

 may be the incident, reflected, or transmitted wave amplitude associated with 

 band, j, so that three values of Qp (incident, reflected, and transmitted) 

 are determined for each irregular wave run. Qp was selected as the parameter 

 to describe the spectral peakedness because it is an especially stable parameter 

 not strongly influenced by the spectral techniques used to determine its value 

 (Rye, 1977). The higher the value of Qp , the more peaked a spectrum. For 

 example, white noise has a Qp value of 1.0, a Pierson-Moskowitz spectrum a 

 value of 2.0, and JONSWAP values of Qp vary between 3.0 and 9.0 with a value 

 of 3.15 for the mean JONSWAP spectrum (Fig. 3). Values of Qp associated with 

 several incident wave spectra used in this study are illustrated in Figure 4. 



rx 



Description Op 



MEAN JONSWAP 3.15 



Pierson-Moskowitz 2.0 



Noise 1.0 



Figure 3. The spectral peakedness, Qp 

 for various spectral shapes. 



17 



