LABORATORY EFFECTS IN BEACH STUDIES 

 VolLime III. Movable-Bed Experiments With H^/L^ = 0.021 (1971) 



by 



Charles B. Chesnutt and Robert P. Stafford 



I. INTRODUCTION 

 1. Background . 



Profiles in movable-bed, coastal engineering laboratory experiments 

 and models with constant wave and sediment conditions are expected to 

 reach an equilibrium shape after a sufficiently long time. Laboratory 

 studies of longshore transport often depend on having an equilibrium 

 profile to accurately determine the longshore transport rate (Savage, 

 1959, 1962; Fairchild, 1970a) . Coastal engineering models are frequently 

 based on simulating an equilibrium profile, which implies a profile whose 

 mean position is fixed in space for the given wave and sediment condi- 

 tions, with the expectation that the actual profile at any given time 

 will deviate from the mean profile. However, equilibrium profiles are 

 not always easily attained (Savage, 1962; Fairchild, 1970a) . 



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 

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

 laboratory experiments were conducted from 1970 to 1972 in the CERC 

 Shore Processes Test Basin (SPTB) to measure the variations in reflec- 

 tion as the profile developed toward equilibrium. The 10 experiments 

 are described in an 8-volume series of reports; this study is Voliime III 

 of the series. An extended discussion of the contents and purposes of 

 this series is available in Volume I (Stafford and Chesnutt, 1977). 



The first two experiments discussed in Volume II (Chesnutt and 

 Stafford, 1977) led directly to the two experiments described in this 

 report. These two experiments were conducted primarily to relate the 

 variation in wave height to changes in the movable-bed profile. The 

 experiments were 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 had reached equilibrium, and the two experiments were continued 

 by periodically adding sand to the backshore. Even with the periodic 

 nourishment, the profile never reached equilibrium and the wave heights 

 remained variable. 



