2. Longshore Current Profile . 



The original model of Longuet-Higgins (1970) for longshore current 

 profile in dimensionless form was compared with the experiments by Galvin 

 and Eagleson (1965). Figure 58 reproduces the results. The small numbers 

 in Figure 58 represent different wave periods tested (e.g., plotted point 

 2=1 second wave period; see Longuet-Higgins, 1972b for key). The labora- 

 tory observations generally lie between P = 0.1 and P = 0.4 which corres- 

 ponded to a lateral mixing coefficient, N in the range between 0.0024 and 

 0.0096, respectively. The bottom friction coefficient, Cf was assumed 

 constant at 0.01. As shown, large variations in P produce relative small 

 changes in longshore current velocity; however, it is very dependent upon 

 Cf which directly influences the reference velocity v-^* . Longuet-Higgins 

 (1972b) felt the lateral mixing and bottom friction effects were too large 

 outside the surf zone. In addition, the neglect of wave setup and use 

 of Y = 0.82 in the theory when the experiments by Galvin and Eagleson (1965) 

 were on a steep beach (tan 3 = 0.11) must be noted when analyzing these 

 results. 



Vm (loci) 



Figure 58. Original longshore current profile theory versus laboratory 



data of Galvin and Eagleson, 1965 (after Longuet-Higgins, 1970) 



172 



