X 



Figure 2 illustrates some conditions assumed to occur nearshore. The 

 local significant wave height (H a defined as the average height of the 

 highest one-third waves) is one of the most important parameters to de- 

 signers. For design curves that give the maximum, mean, or root-mean- 

 square wave height or wave setup, see beeiig and Ahrens (in preparation, 

 1979) 4 . 



II. METHODS FOR USING THE DESIGN CURVES 



The design curves (Figs. 3 to 6) are plots of local significant wave 

 height divided by- the Stillwater depth, Hg/d, versus the ratio of 

 d/gT 2 . Curves are given for various deepwater wave steepness, H^/gT . 

 The bottom slope, m, is the average slope one-half to one wavelength 

 seaward of the point of interest. The location of the transition between 

 wave setup and setdown is shown on each curve (where S^ changes from 

 positive to negative) . The ratio Hg/d may be large because the effec- 

 tive water depth may be greater than the Stillwater depth due to wave 

 setup. Where setup is positive the effective water depth is greater than 

 the Stillwater depth. The method of presenting the data was selected 

 because nearshore wave height can be predicted from deepwater wave con- 

 ditions (method 1, described below) or alternatively, waves measured in 

 finite depth water can be used to estimate wave height at other shallower 

 depths (method 2, described below). For values that fall between the 

 curves use linear interpolation; for bottom slopes flatter than 1 on 100 

 use Figure 3. In some cases more detailed calculations or examination of 

 wave height distribution may be necessary. If so, the computer program 

 GODAS (720X1R1CB0) may be used to predict wave height distributions. This 

 program may be obtained from the Coastal Engineering Research Center, 

 Automatic Data Processing Coordinator, Kingman Building, Fort Belvoir, 

 Virginia 22060. 



The computer program assumes that deepwater wave heights have a Ray- 

 leigh distribution. If in a design situation the deepwater waves are 

 known to be non-Ray leigh, which may occur with multipeaked spectra, the 

 deepwater height distribution in the computer program can be changed to 

 the assumed distribution function and the program used directly to make 

 predictions. 



The analytical model assumes that the water depth is continuously 

 decreasing from deepwater shoreward, and it is not shown what effects 

 offshore bars have on nearshore wave height. As a first approximation 

 for coasts with offshore bars, the wave height shoreward of the bar should 

 be taken as equal to the predicted height at the bar crest location 

 (Y. Goda, Port and Harbour Research Facilities, Tokyo, Japan, personal 

 communication, 1978). At locations shoreward of the bar where the water 

 depth is less than the depth at the bar crest, the methodology can be 

 used to predict wave heights. 



4 SEELIG, W., and AHRENS, J., op. cit., p. 7. 



