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Title: Laboratory effects in beach studies, volume 8: analysis of results from 10 movable-bed experiments
Authors: Chesnutt, Charles B.
Keywords: Breakers
Beach profiles
Coastal engineering
Model studies
Movable-bed experiments
Wave envelopes
Wave generators
Wave height variability
Wave reflection
Wave tanks
Publisher: Coastal Engineering Research Center (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Miscellaneous report (Coastal Engineering Research Center (U.S.)) ; no. 77-7 v. 8.
Description: Miscellaneous Report
Abstract: Variation in wave reflection from a movable bed as it adjusted to the impinging waves was the primary source of wave height variability in 10 experiments in 6- and 10-foot-wide wave tanks. Re-reflection of waves from the wave generator, secondary waves, Transverse waves, and cross waves also contributed to the wave height variability. The reflection coefficient, KR, variation ranged from 0.02 to 0.12 in one experiment to as much as from 0.04 to 0.27 in another experiment. Changes in the foreshore slope and berm-crest elevation, the breaker type, the slope and top elevation of the offshore slope, and the distance between the foreshore and offshore were the sources of the KR variability. For a constant initial profile slope, the average KR increased with increasing wavelength; but for a constant wavelength, the average KR decreased with increasing initial profile slope. In nine experiments the KR tended to increase as the profile developed, indicating that the profile was reflecting, rather than absorbing, energy. Profile equilibrium was not easily attained, particularly in five experiments with a wave steepness of 0.021, which is in the transition region between "winter" and "summer" waves. Experiments with winter or summer waves reached equilibrium more readily. Laboratory effects, caused by differences in initial profile slope, initial test length (distance between the wave generator and the initial shoreline), tank width, and water temperature, affected the profile development and the wave height variability. Initial profile slope and initial test length should be kept constant to assure test repeatability in movable-bed experiments. The wavelength-to-tank width ratio should be greater than or equal to 3 to assure two dimensionality of profile development, but two-dimensional profiles may not be realistic replications of three-dimensional profiles. Note: The reflection coefficient, KR, is not represented accurately in this online abstract due to character set limitations. The downloaded pdf will contain an accurate representation.
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Rights: Approved for Public Release, Distribution is Unlimited
Appears in Collections:Miscellaneous Report

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