Data Observations and 

 Analyses 



28 



Waves 



Seventeen months of high quaUty directional wave data were collected with 

 Puv and DWG gages as described in Chapter 3, plus an additional seven 

 months of lower quality data. Unless specifically stated, the lower quality data 

 are not included in the discussion below. The measured wave data obtained 

 from both sensor types were first transformed to fluctuations in sea surface 

 elevation using a cosh k(z+d) I cosh kd factor (where k is the wave number 

 {— 27:/wave length), z is the (negative) sensor depth, and d is the water depth). 

 Secondly, energy-frequency-direction spectra were computed for each sampling 

 interval using the standard methods of Longuet-Higgins, Cartwright, and 

 Smith (1963). All wave heights in this report refer to H^, calculated as 

 four times the square root of the variance of the record. This value is 

 essentially equivalent to the significant wave height. The peak period {Tp) and 

 direction (Z)^) refer to the period and direction of the maximum energy band of 

 the spectrum. Direction is the direction the waves are coming from. 



The mean (average) wave height for the entire measurement interval was 

 0.6 m, and the mean peak period was 5.9 sec. Though some scatter was 

 observed in the monthly wave data, there was a trend toward lower height and 

 shorter period waves in the late summer and fall (August-October), as shown in 

 Figures 11 and 12. Monthly percent occurrence of wave heights and periods 

 are given in Appendix A, and the monthly height, period, and direction 

 simimaries of the wave data are given in Appendix B. 



The highest H^ in the record is 2.42 m on 27 November 1990. Over the 

 17-month interval of data collection, only six storms produced wave heights in 

 excess of 2 m. The duration of those maximum storm events was usually less 

 than a day. This is comparable to the WES's Wave Information Smdy (WIS) 

 wave hindcast information (Hubertz and Brooks 1989) from station 9 in the 

 Gulf of Mexico. The WIS significant wave height that is exceeded 12 hr/year 

 is determined to be 2.5 m, with a corresponding period of approximately 

 9.1 sec. 



Chapter 4 Data Observations and Analyses 



