The quality and quantity of available data often do not justify 

 elaborate statistical analysis. Even where adequate data are available, 

 a simple characterization of wave climate meets many engineering needs. 

 While mean values of height and, to a lesser degree, period are useful, 

 data on wave direction are generally of insufficient quality for even 

 mean value use. Table 4-4 compiles mean annual wave heights collected 

 from a number of wave gages and by visual observers along the coasts of 

 the United States. Visual observations were made from the beach of waves 

 near breaking. The gages were fixed in depths of 10 to 28 feet. 



Wave data treated in this section are limited to nearshore observa- 

 tions and measurements. Consequently waves were fully refracted and had 

 been fully affected by bottom friction, percolation, and nonlinear changes 

 in wave form by shoaling. Thus, these data differ from data that would 

 be obtained by simple shoaling calculations based on the deepwater wave 

 statistics. In addition, data are normally lacking for the rarer, high- 

 wave events. For these reasons, the data should not be used for struc- 

 tural design, since they are only applicable to the particular site 

 where they were obtained. Normal design practice is based on deepwater 

 wave statistics which are then adjusted to the shallow-site conditions. 

 However, the nearshore data are useful in littoral transport calculations. 



Mean wave height and period from a number of visual observations by 

 coastguardmen at shore stations are plotted by month in Figures 4-10 and 

 4-11, using the average values of stations within each of five coastal 

 segments. Table 4-4 and Figures 4-10 and 4-11 show average values char- 

 acteristic of the wave climate in exposed coastal localities. Visual 

 height data represent an average value of the higher waves just before 

 they first break. The data provide only approximate indications of the 

 height distributions, but mean values of these distributions are useful. 



In Figure 4-10 the minimum monthly mean littoral zone wave height 

 averaged for the California, Oregon, and Washington coasts exceeds the 

 maxirmm mean littoral zone wave height averaged for the other coasts. 

 This difference greatly affects the potential for sediment transport in 

 the respective littoral zones, and should be considered by engineers 

 when applying experience gained in a locality with one nearshore wave 

 climate to a problem at a locality with another wave climate. 



4.332 Mean vs Extreme Conditions . Section 3.22 contains a discussion 

 of wave height distributions and the relations between various wave 

 height statistics, such as the mean, significant, and RMS heights, and 

 extreme values. In general, a group of waves from the same record can be 

 approximately described by a Rayleigh distribution. (See Section 3.22.) 

 However, a different distribution appears necessary to describe the dis- 

 tribution of significant wave heights, where each significant wave height 

 is from a different wave record at the locality. (See Figure 4-12.) 



Visual analysis of waves recorded on chart paper is discussed in 

 Section 3.22 and by Draper (1967), Tucker (1963), Harris (1970), and 

 Magoon (1970). Spectrum analysis of wave records is discussed in 



4-30 



