Since there is considerable variability in wave height and wave length 

 in the waves leaving a generating area,, it is necessary to define statisti- 

 cally the sigiificance of the waves „ Actually the higher waves are the 

 most important from an engineering standpoint! hence, in stating the mean 

 height of the waves that exist over a period of an hour or two it is ad- 

 visable to consider only the higher of the waves that are present,, Ob- 

 viously, every ripple should not enter into forming an average „ As a con- 

 sequence of these considerations the present practice in stating the 

 average wave height is to give the average height of the higher one-third 

 of all observed waves „ Where the observation is precise , as in analyzing 

 the records of wave recorders , the average of the higher one-third of the 

 major train of waves is used This average is called the "significant 

 wave height" 



Compilation of Design Data 



An engineer engaged in the design of coastal works must have a method 

 of estimating the highest waves which might be expected due to a given 

 design wind or, perhaps of more importance s he should have adequate data 

 on the characteristics of the waves to be expected for the different 

 seasons at any particular pointo For the engineer engaged in construction 

 work or in handling floating equipment^ statistical information alone is 

 insufficient for his operations „ He must have definite information on the 

 wave conditions that will exist at the time of his operations Methods 

 and instruments for providing such information are available and are now 

 in use Statistical data on the frequency of occurrence of waves of various 

 heights at any given locality can be assembled from direct observation 

 over a period of time, much as is done in assembling stream flow data for 

 flood-flow predictions o This procedure, of course, requires the installa- 

 tion of suitable recorders for measurement of the height and period of the 

 waves o Several years of record also must be assembled before reliable 

 average conditions can be determined 



The Department of Engineering at the University of California, in 

 cooperation with the U„ So Navy, has had wave recorders in operation for 

 almost a year at Point Sur, California, and Hecta Head s Oregon,, These 

 recorders will provide sufficient coverage of the Pacific coast to permit 

 a compilation of statistical data on wave conditions at selected points 

 along the coasto Wave data for intermediate localities can be estimated 

 by interpolation „ Records from the wave records also provide a means of 

 checking the method of forecasting waves from weather charts as discussed 

 later,, 



A brief discussion of the instruments which have been developed for 

 recording waves is of interest at this pointo For coastal points, the 

 swell, as previously mentioned, is the predominate factor to consider in 

 the design of structures! hence, wave recorders such as those installed 

 on the Pacific coast are designed for obtaining information on only the 

 larger waves or what is called the "significant" waves „ Of the various 

 recorders which have been developed by the University of California, all 



