The LEBS experiments were planned to be run until the profile devel- 

 oped an equilibrium shape because it was assumed that if the profile 

 reached equilibrium, the primary source of temporal wave height varia- 

 bility, the changing profile reflectivity, would be eliminated or sig- 

 nificantly reduced. 



The effects of varying initial slope and wave period are discussed 

 below. The effect of tank width on profile development is discussed in 

 Section IV. 



2. Effect of Initial Profile Slope . 



Two experiments were conducted in which the only variable was the 

 initial profile slope--0.10 in experiment 71Y-06 and 0.05 in experiment 

 72D-06. 



The steeper initial slope in experiment 71Y-06 (Fig. 12) adjusted 

 slowly to the waves and did not appear to have reached equilibrium along 

 any segment of the profile after 375 hours. The foreshore retreated at 

 a rate of 0.113 foot (3.44 centimeters) per hour between 1 and 15 hours 

 and at a rate of 0.025 foot (0.76 centimeter) per hour thereafter. The 

 flat shelf in the inshore zone and the steeper slope in the offshore zone 

 developed between 200 and 220 hours. 



The flatter initial slope in experiment 72D-06 (Fig. 13) adjusted 

 more quickly to the wave attack, but also did not appear to have reached 

 equilibrium. The foreshore retreated at a rate of 0.05 foot per hour 

 between 5 and 125 hours, prograded seaward between 125 and 135 hours, 

 and then stabilized for the remainder of the experiment. The inshore 

 zone slowly grew in width and the offshore slope remained mild during 

 the first 100 hours. After 100 hours the flat shelf in the inshore zone 

 and the steeper slope in the offshore zone rapidly developed. Once the 

 foreshore stabilized, the inshore zone began eroding, creating a signifi- 

 cant depression in the profile below the forshore zone, while the off- 

 shore zone continued to prograde seaward. The K^, stopped varying 

 during the last 25 hours (Fig. 7), indicating that equilibrium may have 

 been near. 



Although neither profile reached equilibrium, the profiles developed 

 somewhat different shapes (Fig. 14). The differences in rates and types 

 of profile adjustments verify the conclusions of Collins and Chesnutt 

 (1975, 1976) that the initial profile slope can affect the final profile 

 shape. 



3. Effect of Wave Period . 



Nine experiments were conducted with an initial profile slope of 

 0.10 and four different wave periods; the experiments are analyzed below 

 to determine the effect of wave steepness on profile equilibrium. The 

 deepwater wave steepness was 0.039 for the 1.50-second wave, 0.021 for 

 the 1.90-second wave, 0.013 for the 2.35-second wave, and 0.004 for the 

 3.75-second wave. 



51 



