An Effect of Permeability on Sand Transport by Waves.
Abstract
Permeability effects on the movement of sand in oscillatory flows are observed in laboratory experiments which approximate prototype conditions at the seabed under progressive waves. A natural sand is used, wave periods range between 3 and 14 seconds, and sand surfaces are naturally rippled. The apparatus has a symmetry which removes all effects, except those of permeability, which might cause a net movement of sand. Onshore and offshore directions are determined by phase relationships between the horizontal flows and superposed vertical permeability flows. A positive permeability effect is found, in that the ripple profiles move in the onshore direction. The velocity of this motion is measured and described in a simple dimensionless plot. The associated net transport of sand is not observed directly but can be inferred, to an extent, from the motions of the ripple profiles. The effects of permeability are cumulative and can be significant in coastal processes of long duration. Any estimate of the local rate of sand transport onshore due to permeability involves the distribution of permeabilities within the seabed which are largely unknown. An overall estimate is less than 1 cubic meter per meter of shoreline per year, which is negligible for most engineering considerations. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1975
- Accession Number
- ADA020641
Entities
People
- Karl E. B. Lofquist
Organizations
- National Institute of Standards and Technology