LABORATORY EFFECTS IN BEACH STUDIES 



Volume VIII. Analysis of Results from 10 Movable-Bed Experiments 



by 

 Charles B. Chesnutt 



I. INTRODUCTION 



Laboratory effects, caused by differences in tank width, initial 

 slope, distance between the generator and the profile, gaps at the end 

 of the generator blade, and, perhaps, even water temperature, can hinder 

 the solution of coastal engineering problems in movable-bed laboratory 

 studies by distorting the development of the movable-bed profile and 

 causing spatial and temporal variations in the wave height. Temporal 

 wave height variability caused by the changing reflectivity of the 

 developing profile complicates the study of the laboratory effects, as 

 well as the investigation of coastal engineering problems. Temporal 

 reflection variability would presumably be eliminated after the profile 

 reached equilibrium, but equilibrium is difficult to define and attain 

 in the laboratory. 



1. Background . 



The Laboratory Effects in Beach Studies (LEBS) project (called the 

 Wave Height Variability project until 1971) was initiated in 1966 to 

 investigate the sources of and possible solutions to the wave height 

 variability observed in longshore transport experiments at the Coastal 

 Engineering Research Center (CERC) in the late 1950' s and early 1960 's. 

 Three-dimensional experiments were performed in 1967 to isolate the 

 major sources of wave height variability. The superposition of incident 

 and reflected waves was found to be a major source of spatial variability, 

 and changes in the profile reflectivity was found to be a major source of 

 temporal variability. 



Two-dimensional tests were performed in 1968 and 1969 to study wave 

 reflection and served mainly to develop improved techniques for collecting 

 and reducing profile surveys and wave reflection data. 



During 1970 to 1972, 10 lengthy experiments were conducted to define 

 the amount of wave height variability due to wave reflection and varia- 

 tion in reflection. These experiments were to be continued until the 

 profile reached equilibrium and the temporal wave height variability 

 ceased. The effect of tank width was to be studied by conducting tests 

 in both 6- and 10-foot-wide (1.8 and 3.0 meters) tanks. The results of 

 these experiments have also pointed out other laboratory effects. 



2. LEBS Reports . 



This report (Vol. VIII), the last of a series of eight volumes on 

 LEBS, analyzes the results of the 10 experiments. 



