The experimental values of the reflection coefficient were obtained 

 from Healy's formula (Eagleson and Dean, 1966} 



IT - H 



_ mag " min (-61) 



^ " H + H . ' 

 max mm 



where H is the maximum wave height (measured at the antinode) and 

 H . is^the minimum wave height (measured at the node) of the wave 

 envelope in the reflected wave region. Equation (61) shows that H^j^^ 

 is considerably smaller than Hj^^ when the reflection coefficient 

 approaches unity. If it is assumed that Hj^a.x ^^ correctly determined 

 but the value obtained for the minimum wave height incorporates an 

 error, A, equation (61) may be written 



H - H . -^ H - H .^ 

 max mm max mm 



H + H . , A 

 max mm 1 + 



(62) 



H + H . 

 max mm 



in which Hj^^^ and* H^^j^ are assumed to be the true values. The error, 

 A, in the experimental determination of iiff^in ^^^^ generally be positive 

 due to nonlinear effects. Equation (62) therefore shows that the 

 experimentally determined reflection coefficient will be lower than the 

 true reflection coefficient due to the measurement error, A. This 

 problem is addressed in detail in Section III. 3; here it is just pointed 

 out to illustrate that one must pay special attention to minimizing the 

 experimental error in the determination of Hj^j^j^. No particular 

 attention was paid to this problem by Wilson (1971) who applied 

 equation (61) directly. It is clear from equation (62) that with the 

 error A increasing with increasing nonlinearity of the incident waves, 

 i.e., with increasing Hj^/L, a trend of determining an experimental 

 reflection coefficient which decreases with incident wave height results, 

 This may partly explain the behavior of the experimentally determined 

 reflection coefficients in Figures 6,7, and 8 as being nearly constant 

 with H-j^/L whereas the predicted reflection coefficients show R to 

 increase with increasing values of Hj^/L. 



Since Wilson's (1971) experiments essentially correspond to scale 

 models of the same structure, performed for different length scales, 

 these experiments give an excellent exposition of the scale effects 

 associated with hydraulic-model tests of porous structures. It is seen 

 from the generally good agreement between predicted and observed 

 transmission coefficients that the present analytical procedure may be 

 used with confidence in assessing the influence of scale effects on 

 experiments of this type. The Froude model criterion applies only so 

 long as the flow resistance is predominantly turbulent, i.e., f is 



36 



