average H^. Differences in this distance also affect the phase of 

 secondary waves at the toe of the profile. The effect of secondary 

 waves was shown by differences in the shape of the offshore zone in two 

 pairs of experiments. 



(c) Three special and one general tank width effects were observed. 

 Strong circulation currents developed over the profile between antinodes 

 of the standing wave for a wavelength four times the tank width, which 

 affected the profile development and reflectivity. Cross waves occurred 

 over a short segment of the profile for a brief time in one experiment, 

 but the effect was not measured. Transverse waves generated by the gap 

 at the end of the generator blade caused significant lateral variations 

 in one experiment, but were not observed in the experiment with the same 

 wave period but different tank width and initial test length and without 

 a gap. In general, as the wavelength-to-tank width ratio increased from 

 1, the amount of lateral variation in profile development decreased. 



(d) Two different effects of water temperature variation were 

 observed. Six experiments support, to varying extents, the hypothesis 

 that the higher the water temperature, the lower the recession rate. 

 Two experiments support the opposite effect, that the higher the water 

 temperature, the higher the recession rate. Another experiment supports 

 either hypothesis. 



VI. RECOMMENDATIONS FOR CONDUCTING MOVABLE-BED COASTAL EXPERIMENTS 



1. Modeling Criterion . 



Equilibrium profiles are not often found in the prototype, and thus 

 they may not be necessary to replicate. Also, equilibrium profiles are 

 difficult to attain in the laboratory and may not be repeatable when 

 they are reached. Therefore, it is recommended that some other criteria 

 be selected as the prototype condition for replication in the laboratory, 

 such as constant rate of shoreline recession or volume erosion. 



2. Tank Setup and Test Conditions . 



(a) The initial distance from the generator to the shoreline must be 

 held constant when attempting to perform repeatable profile experiments. 



(b) The initial slope can affect the profile development and should 

 be held constant to assure test repeatability. 



(c) To eliminate lateral variations in profile shape due to too 

 short a crest length, wavelengths greater than three times the tank 

 width should be chosen. However, two-dimensional tests may distort a 

 three-dimensional problem to an unknown extent. 



(d) The water temperature should be kept within a 5° Celsius range 

 to assure test repeatability. 



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