The predicted wave height at gage 610 is then found by equation (1) to be 



-1 



Hs610 = (0.984)(2.0) 



(0.004)(2.0) 



(1.29) + 1 



= 1.91 meters 



(0.0036)(100) 

 *************************************** 



V. SUMMARY AND CONCLUSIONS 



The combined effect of shoaling and bottom friction is underpredicted an 

 average deviation of 6 percent by Bretschneider and Reid's (1954) theory, 

 based on 31 observations. This study indicates that care must be taken in 

 applying the predictive theory when wave spectra are broad or multipeaked, or 

 when the bathymetry is irregular and the bottom contours are not straight and 

 parallel. 



For parallel bottom contour cases, the largest deviations from observed 

 wave conditions arise when the wave spectrum which corresponds to the sig- 

 nificant wave characteristics is broad or multipeaked. These large devia- 

 tions, due to the presence of large amounts of energy relative to the total 

 energy of the spectrum in many wave components, indicate that the significant 

 wave height may not be a representative number to use for calculations in the 

 equations when the spectrum is not narrow and single-peaked. 



The calculations in Table 3 show that caution must be taken when using the 

 equations in areas of irregular bathymetry or near coastal structures where 

 the bathymetry may not be uniform. Other types of wave attenuation processes 

 become important in these cases, with refraction being particularly dominant 

 when the contours are not parallel and other bottom irregularities such as 

 holes and shoals are present. 



The choice of the friction coefficient will also play a role in com- 

 pounding the predicted wave height deviation from actual observations. The 

 coefficients used here are a result of controlled laboratory studies and, 

 therefore, may not be a true representation of field coefficients. The 

 presence of bottom ripples is not considered in this analysis, but has been 

 shown to be a variable in* determining the friction coefficient. Also, linear 

 theory is used to calculate bottom velocity and horizontal water particle 

 displacement; higher order calculations may lower present deviations. 



14 



