Figure 34. 



86 



Pressure data from Burns Harbor, Indiana, April 6, 1988. This plot shows how 

 dramatically the energy can increase in only a few hours 



wave spectra. The types of wave statistics needed vary depending on the 

 application. For example, a geologist might want to know what the average 

 wave period, height, and peak direction are along a stretch of the shoreline. 

 This information could then be used to estimate wave refraction and longshore 

 drift. An engineer who is building a structure along the shore would be 

 interested in the height, period, and approach direction of storm waves. He 

 would use these values to calculate stone size for his structure. Table 12 lists 

 common statistical wave parameters. 



Table 12 is intended to underscore that wave analyses are complex proce- 

 dures and should be undertaken by coastal researchers with knowledge of 

 wave mechanics and oceanography. In addition, researchers are urged to be 

 cautious of wave statistics from secondary sources and to be aware of how 

 terms have been defined and statistics calculated. For example, the term 

 "significant wave height" is defined as the average height of the highest one- 

 third of the waves in a record (Shore Protection Manual 1984). How long 

 should this record be? Are the waves measured in the time domain by 

 counting the wave upcrossings or downcrossings? The two methods may not 

 produce the same value of H s . Might it not be better to estimate significant 

 wave height by performing spectral analysis of a wave time series in the 

 frequency domain and equating H s = H m0 l This is the procedure commonly 

 used in experiments where large amounts of data are processed. The latter 



Chapter 5 Analysis and Interpretation of Coastal Data 



