Wave Records 



Importance of wave measurements 



The measurement and analysis of wave data are of paramount importance 

 to the understanding of coastal processes. The following quote from the 

 Shore Protection Manual (1984) underscores reasons for obtaining wave 

 parameters from the coastal zone: 



Waves are the major factor in determining the geometry and compo- 

 sition of beaches and significantly influence the planning and design 

 of harbors, waterways, shore protection measures, coastal structures, 

 and other coastal works. Surface waves generally derive their 

 energy from the winds. A significant amount of this wave energy is 

 finally dissipated in the nearshore region and on the beaches. 



Waves provide an important energy source for forming beaches; 

 sorting bottom sediments on the shoreface; transporting bottom 

 materials onshore, offshore, and alongshore; and for causing many 

 of the forces to which coastal structures are subjected. An adequate 

 understanding of the fundamental physical processes in surface wave 

 generation and propagation must precede any attempt to understand 

 complex water motion in the nearshore areas of large bodies of 

 water. Consequently, an understanding of the mechanics of wave 

 motion is essential in the planning and design of coastal works. 



To an observer on the shore or on a boat, the sea surface usually appears 

 as a chaotic jumble of waves of various heights and periods, moving in many 

 different directions. Wave gages measure and record the changing elevation 

 of the water surface. Unfortunately, these data, when simply plotted against 

 time, reflect the complexities of the sea's surface and provide little initial 

 information about the characteristics of the individual waves that were present 

 at the time the record was being made (Figure 30). Once the water elevation 

 data are acquired, further processing is necessary in order to obtain wave 

 statistics that can be used by coastal scientists or engineers to infer which 

 wave forces have influenced their study area. 



Wave data analysis typically consists of a series of steps: 



Data transfer from gage to computer. 



Conversion of data from voltage readings to engineering units. 



Initial quality control inspection. 



Spectral analysis. 



Additional quality control (if necessary). 



Summary statistics in table and plot form. 



Plots of individual wave bursts or special processing. 



81 



Chapter 5 Analysis and Interpretation of Coastal Data 



