the outer offshore below -1.9 feet remained unchanged throughout the 

 experiment. The differences in foreshore berm-crest elevation may have 

 resulted from the differences in the outer offshore, but these cannot be 

 determined. 



c. Initial Slope Effect . The effect of varying the initial slope 

 can be seen by comparing experiment 71Y-06 with an initial slope of 0.10 

 and experiment 72D-06 with an initial slope of 0.05. All other parameters 

 were equal in these two experiments. 



In each of these experiments the effect of re-reflection on the inci- 

 dent wave height variability was the same (0.03 foot), but there was a 

 0.02- foot difference in average incident wave height (Table 13). Re- 

 reflection caused a higher average incident wave height in the experi- 

 ment with the flatter initial slope. 



The distance from the generator to the toe of the initial slope was 

 23 feet greater in experiment 71Y-06 (0.10 slope); thus, the velocity 

 distribution at the toe of the slope may have been different in the two 

 experiments . 



The offshore profiles in these two experiments developed similar 

 shapes (Fig. 14), but the inshore zone developed somewhat differently. 

 In experiment 72D-06 (0.05 initial slope) the flat shelf in the inshore 

 zone developed during the first 100 hours and a trough was scoured in 

 the zone after the foreshore stabilized at 135 hours. In experiment 

 71Y-06 (0.10 initial slope) the flat shelf in the inshore zone developed 

 between 200 and 220 hours and then continued to widen as the foreshore 

 and offshore separated. 



It is not possible to ascertain whether re-reflection, secondary 

 waves, or some other phenomena caused the profiles to develop such 

 different inshores, but it was probably the result of the difference 

 in initial slope. 



3. Tank Width Effects. 



When the wavelength, L, is much larger than the tank width, W, 

 then the wave tank is "narrow" and the result of wave action on the sand 

 bed is expected to be two dimensional; i.e., without lateral variations 

 in profile shape. When L is much smaller than W, then the wave tank 

 is essentially a "basin" and the result of wave action on the sand bed, 

 even when wave direction is normal to the initial shoreline, is expected 

 to be three dimensional; i.e., with lateral variations in profile shape. 

 In the intermediate case, when the tank width and wavelength are nearly 

 the same (L/W - 1) , the wave tank is wide enough for the lateral varia- 

 tions to begin to occur, but the tank walls confine the third dimension 

 of current patterns and sediment movement to an unknown extent. In the 

 10 LEBS experiments, L had values that ranged from equal to W to 

 several times larger than W, so the point at which a wave tank becomes 

 narrow can be examined. 



79 



