the percentages associated with kurtosis values in Figures 25 and 26 

 higher than about 4 should be considered somewhat inflated. 



The correlation between skewness and peak spectral period is less 

 than 0.25 at all locations; for single-peaked cases it is similarly low. 

 However, the correlation between skewness and significant height is 

 moderatly high for the ocean and gulf coast locations (Table 8). There 

 is a clear tendency for skewness to increase with significant height for 

 the ocean and gulf coast locations as evidenced in a plot of mean skew- 

 ness versus significant height (Fig. 27) . This tendency is not evident 

 for the Great Lakes locations (Fig. 28) . 



It is apparent that cnoidal wave profiles (see Fig. 2) with very 

 high skewness and kurtosis values are rarely observed at the selected 

 gage locations. However, some of the records contain wave profiles which 

 are more nearly cnoidal than sinusoidal. Figures 24, 25, and 26 indi- 

 cate that cnoidal profiles appear in about 10 percent of the records or 

 less. 



V. CONCLUSIONS 



The following conclusions are drawn from evidence and discussion 

 presented in this report: 



1. About 60 to 70 percent of the ocean and gulf coast energy spectra 

 in shallow water have one or more major peaks in addition to the dominant 

 peak. 



2. At least 50 percent of the spectra in Lakes Michigan and Erie 

 have one or more major secondary peaks. 



3. Major secondary spectral peaks are common for both high and low 

 energy spectra. 



4. The very small sample of spectra for hurricane waves examined 

 (seven spectra) does not reveal any special characteristics of hurricane- 

 generated spectra. 



5. Major secondary spectral peaks are usually indicative of secondary 

 wave trains. 



6. When secondary spectral peaks occur at frequencies of two or three 

 times the dominant frequency, they may represent a single train of steep 

 waves rather than independent wave trains, especially if the relative 

 water depth for the dominant wave is small. 



7. When secondary spectral peaks occur at frequencies of 0.5 or 1.5 

 times the dominant frequency and the waves are high enough for breaking 

 to occur, the secondary peaks may not represent independent wave trains. 



54 



