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Cross-shore sediment transport on mixed sand and gravel beaches

University of British Columbia

Cross-shore (onshore-offshore) sediment transport has been studied to determine the importance of sediment permeability on the equilibrium beach slope. Quick (1991) has proposed that the permeability of the beach material effects the onshore-offshore transport by changing the stresses on the beach through the infiltration and exfiltration processes. Based on Hazen's (1911) idea that the sediment's D₁₀ value (that is, 10% of the material is finer than this value) may be used to represent its permeability, Quick developed a relationship between the wave height, the sediment D₆₀ value, the D₁₀ value and the equilibrium beach slope. Three series of experiments which used sand (D₅₀=0.59 mm) and gravel (D₅₀=5.5 mm) in varying proportions to represent a range of permeabilities. Gravel and sand beaches were exposed to wave action and the resulting beach profiles noted. Mixtures of the two sediments were then put through the same tests and their equilibrium beach profiles measured. From this data, it was found that as little as 25% (by volume) sand could cause a gravel beach to behave much like a sand beach. The beach permeability was an important factor in determining beach response to wave conditions, along with the wave height. Further experimental work is necessary in order to determine the minimal amount of sand required to shift a gravel beach's response to wave attack. The fact that so little sand is require to make the shift, caution is necessary when designing artificial beaches and in modifying existing beaches.

Thesis/Dissertation

application/pdf

2009-04-28

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http://hdl.handle.net/2429/7668

Civil Engineering

University of British Columbia

UBCV

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