m> mxm 

 mxm 



'lOcm/nc 



/ ^ 



LONGSHORE (m) 



Figure 67. Typical vectors of 17.1-minute average currents at Torrey 

 Pines, California, from NSTS experiments (after Guza and 

 Thornton, 1980). 



currently being obtained at the Delft Technical University (see Visser, 

 1980) should provide the needed information to verify the theory in the 

 near future. The data of Galvin and Eagleson (1965) and others are simply 

 inadequate for this purpose. This is true for both regular (linear and 

 nonlinear) and irregular theories. 



3. Nonlinear and Irregular Waves . 



The nonlinear theoi^^ of James (1974b) is shown in Figure 68 along 

 with four experiments from Galvin and Eagleson (1965) and their data. 

 Transition between the hyperbolic and Stokes wave theories is indicated 

 by the arrow. Various combinations of friction coefficient Cj and eddy 

 coefficient N are presented. The values indicated for these coefficients 

 give relatively small variations in velocity and are said to give good 

 agreement with the measured velocity shown by crosses. Friction coefficients 

 varied between 0.001 and 0.0025 and eddy coefficients between 0.01 and 

 0.016 in these cases. Figures 38 and 59 showed how the original linear 

 theory required significantly larger bottom friction values (C^ = 0.01) 

 to match the surf zone measurements. The nonlinear theory is also apparen- 

 tly less sensitive to variations in eddy coefficient. 



Collins (1972) and Battjes (1974a) did not attempt any comparisons 

 with laboratory or field data for their irregular wave theories. Sonu 

 (1975) prepared the results presented here as Figure 69 where the random 

 sea model (heavy solid line) is from Collins (1972). It was assumed that 

 the monochromatic wave height is equal to a rms wave height in the irregular 

 sea. For comparison, the original model theory of Longuet-Higgins (1970) 



182 



