variation (0.01 foot or 0.3 centimeter in experiment 70X-06; 0.03 foot or 

 0.9 centimeter in experiment 70X-10) could be attributed to measurement 

 errors or to variation in the generated wave. The remainder of the vari- 

 ation is likely due to re-reflection. 



c. Secondary Waves . Along the length of the tank, between the gen- 

 erator and the toe of the profile, wave heights varied as the result of 

 secondary waves. Galvin (1972) and Hulsbergen (1974) described secondary 

 waves (called solitons by Galvin) and their effects. Secondary waves can 

 be observed on the records, but a detailed analysis of wave shape was not 

 conducted as part of this study. 



2. Profile Equilibrium . 



In conducting experiments which presume the existence of an "equilib- 

 rium" profile, an approximation of that equilibrium profile should be 

 used to start the experiment (see Savage, 1959; Fairchild, 1970a). These 

 experiments were extended over long periods (hours) in hopes of defining 

 the equilibrium profile for the given wave and sediment conditions. The 

 contour position lines or the CONPLT plots in the offshore zone in experi- 

 ment 70X-06 were approaching horizontal (or equilibrium), but the continued 

 erosion from the backshore indicated that equilibrium had not been reached. 

 Experiment 70X-10 showed no evidence that the profile was close to equilib- 

 rium. These results suggest that equilibrium profiles are not easily 

 determined (Chesnutt and Galvin, 1974; Chesnutt, 1975). 



3. Other Laboratory Effects . 



The differences in test conditions (tank width, initial test length, 

 and uncontrolled water temperature) provide possible explanations for the 

 differences in profile shape discussed in Section III, Ic, but also pre- 

 vent a rigorous proof of the effect of any one of these differences as 

 definite causes. Chesnutt (1975) discussed the effects of initial test 

 length and water temperature. 



a. Tank Width . Since lateral variations in profile shape occur on 

 natural beaches, the occurrence of lateral variations in the two tanks is 

 an expected difference. The profile in experiment 70X-06 can be considered 

 a typical two-dimensional profile for the particular wave conditions, but 

 the variations in profile shape in experiment 70X-10 indicate that the 

 distance between the tank walls had an effect on the profile shape. The 

 lateral variations in the 10-foot tank indicate greater three-dimensional 

 movement of sediment; therefore, a longer time is required to move the 

 sediment offshore, accounting for at least part of the difference in rate 

 of change. 



b. Initial Test Length . Changes in the distance from the wave gen- 

 erator to the profile can cause a variation in the velocity field under 

 the waves at the toe of the profile, and therefore affect the rate of 

 profile change in at least two ways. Hulsbergen (1974) has shown that the 



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