higher the temperature the lower the recession rate. Too little useful 

 data are available in experiment 70X-10 to be of any value to the com- 

 parison. 



Experiment 72A-06 supports the opposite hypothesis that an increasing 

 water temperature causes an increasing erosion. Experiment 72C-10 sup- 

 ports this hypothesis or perhaps tends to disprove the other hypothesis 

 in that a decreasing water temperature coincided with a decreasing ero- 

 sion rate. 



Experiment 72A-10 supports either hypothesis since the temperature 

 and the shoreline were both stable. 



5. Other Laboratory Effects . 



The known causes of laboratory effects are summarized in Table 14, 

 classified by physical constraint and by phenomena or parameter affected. 

 The effects of re-reflection, wavelength-to-tank width ratio, transverse 

 waves, and circulation between antinodes were discussed earlier in this 

 section. Secondary waves were observed on the wave records and their 

 effect in a few of the experiments was discussed. Hulsbergen (1974) 

 provides a detailed description of the effects of secondary waves on 

 profile shape. Water temperature was measured and some of the possible 

 effects of changing viscosity were measured, but the results are incon- 

 clusive. Cross waves were observed for a short period of time but their 

 effect could not be measured. 



Four other phenomena can cause laboratory effects , depending on the 

 physical constraints of the individual experiment or facility designs. 



When conducting experiments in a wave basin with training walls and 

 with the waves approaching the shoreline obliquely, the waves reflected 

 from the profile can re-reflect from the down-drift sidewall, then from 

 the generator, from the up-drift sidewall, and then reattack the profile 

 from an entirely different angle. In similar experiments without train- 

 ing walls, re-reflection problems are minimal but diffraction effects 

 and basin resonance become significant sources of variations. Fairchild 

 (1970b) discussed these three interrelated phenomena and their effects. 



Another effect is the difference between a profile shaped by mono- 

 chromatic waves and a profile shaped by irregular waves. Watts (1954) 

 and Watts and Dearduff (1954) examined the effect of varying wave period 

 and water level. The effect of periodic waves could be examined by 

 repeating these experiments with a set of irregular waves having the 

 same energy density. 



V. CONCLUSIONS 



1. Wave Height Variability . 



(a) Variation in reflection from the profile was found to be the 

 major source of wave height variability in 10 movable-bed experiments. 

 The varying phase difference between the wave re-reflected from .the 



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