2. Design Curves . 



Appendixes B and C present formats of design curves obtained from Goda's 

 analytical model (Seelig, 1978). The first format (App. B) includes plots of 

 five variables in the nearshore zone: (a) The maximum wave height, Hi, de- 

 fined as the mean of the highest 1 percent of the waves; (b) the significant 

 wave height, H g , defined as the mean of the highest one-third waves (the 

 significant wave height is approximately equal to four times the root-mean- 

 square (rms) surface elevation of a water level record); (c) the rms wave 

 height, Hp^g; (d) the mean wave height, H; and (e) the wave setup, S w . 

 All of these variables are divided by the deepwater significant wave height. 

 The five variables are plotted on the ordinate versus the ratio of the local 

 Stillwater depth, d, to the deepwater significant wave height, H' on the 

 abscissa. One plot is available for each wave steepness and for each beach 

 slope. 



The second format (App. C) gives the ratio of the local significant wave 

 height divided by the Stillwater depth on the ordinate versus d/(gT 2 ) on the 

 abscissa. 



Both formats give the same information about the significant wave height, 

 but the first format is often more useful when starting with the deepwater 

 parameters H^ and T s . The second format is useful for taking highcast sig- 

 nificant wave heights measured at one water depth and using this information to 

 estimate the significant height at another shallower depth. 



3. Calculation of Nearshore Wave Heights and Water Level Parameters . 



a. Parameters. Parameters needed to use the curves in Appendixes B and C 

 are the equivalent deepwater significant wave height, H^, the representative 

 deepwater wave period, T s , and the offshore bottom slope, m. For an irreg- 

 ular profile, take the average profile slope one-half to one wavelength seaward 

 of the point of interest. 



b. Procedure for Computation of the Offshore Wave Steepness, H^/L, and 

 Depth-to-Height Ratio, d/H^. If H^ is in feet and T g is in seconds, then 



— = 2__ (4) 



L Q (5.12 T|) 



L Q is taken as defined by monochromatic linear theory, so that L can be 

 considered a reference wavelength. The actual wavelengths during irregular 

 wave conditions may be variable and influenced by factors such as spectral 

 shape and wave interaction. The advantage of using linear theory to describe 

 L is that the same wave and setup information can be provided in a more con- 

 venient form than if some nonlinear theory were used to characterize wavelength. 

 If H^ is in meters and T g is in seconds, then 



H' 



(1.56 



(5) 



The ratio of the water depth at the point of interest to H^ is determined by 

 using equation (3) 



d_ 

 H' 



15 



