LABORATORY EFFECTS IN BEACH STUDIES 

 Volume IV. Movable-Bed Experiments with H^/L^ = 0.021 (1972) 



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 Charles B. Chesnutt and Robert P. Stafford 



I. INTRODUCTION 



1. Background . 



Profiles in movable-bed, coastal engineering laboratory experiments and 

 models are expected to reach an equilibrium shape after a sufficiently 

 long time. The equilibrium shape is thought to depend only on constant 

 wave and sediment conditions. The initial slope has been assumed to have 

 no effect on the final shape of the profile. 



The Laboratory Effects in Beach Studies (LEBS) project was initiated at 

 the Coastal Engineering Research Center (CERC) in 1966 to investigate the 

 causes of wave height variability and other problems associated with mov- 

 able-bed coastal engineering studies. Ten movable-bed laboratory experi- 

 ments were conducted from 1970 to 1972 in the CERC Shore Processes Test 

 Basin (SPTB) to measure the variation in reflection as the profile devel- 

 oped toward equilibrium. This report (Vol. IV) discusses the experiment 

 with H^/L^ = 0.021 completed in 1972; Volumes II and III (Chesnutt and 

 Stafford, 1977a, 1977b) discussed the experiments with the same wave 

 steepness, conducted in 1970 and 1971. The other five experiments are 

 discussed in Volumes V to VII, part of a series of eight reports on LEBS. 

 Volume I of the series (Stafford and Chesnutt, 1977) discusses the contents 

 and primary purposes of these reports. The first four experiments with 

 initial slopes of 0.10 (discussed in Vols. II and III) led directly to 

 the experiment described in this report. The first two experiments in 

 1970 (Vol. II) were conducted primarily to relate the variation of wave 

 height to changes in the movable-bed profile. The experiments v/ere to 

 continue until the profile reached equilibrium, at which point it was 

 assumed that the wave height variability would be significantly reduced. 

 However, the beach had eroded to the back of the tank before the profile 

 reached equilibrium. 



The two experiments in 1971 (Vol. Ill) were repeats of the first 

 two, with more sand added so that the initial test length (distance from 

 the wave generator to the initial Stillwater level (SWL intercept) was 

 shortened by 7 feet (2.1 meters) in both tanks. Again, neither profile 

 reached equilibrium. 



The experiment discussed in this study (72D-06) was essentially a re- 

 peat of experiment 71Y-06 in the 6-foot-wide (1.8 meters) wave tank 

 reported in Volume III (initial test length of 93 feet or 28.3 meters) 

 with more sand added so that the initial slope was 0.05. With the addi- 

 tional sand placed at an initial slope closer to the presumed final 



