The effect of fluid acceleration on sediment transport in the surf zone

The surf zone is defined by highly non-linear, breaking waves that have very different acceleration signatures beneath their respective crests and troughs. The consequences of this dissimilarity on sediment transport is not fully understood. This thesis develops methodologies to predict sediment transport under these asymmetric, skewed waves. Two different transport mechanisms are considered: bedload transport and "subsurface" transport. The potential for subsurface transport was first realized by Madsen (1974) who found that the large pressure gradient beneath a breaking wave was sufficient to drive a substantial porous-media flow, adequate to create a soil-mechanics type failure extending several centimeters into a sandy sediment bed. The theoretical model of Madsen (1974) is extended to obtain estimates of subsurface transport by subdividing the sediment in failure into distinct, kinematically admissible slip circles. An equation governing the rotation of each slip circle is developed, yielding the subsurface sediment's horizontal movement as a function of depth. By integration, subsurface transport can predicted. In addition, a method is developed for estimating bedload transport under breaking waves, accounting for the enhanced shear stress beneath the wave's crest. An existing bedload formula is used as the foundation for this predictive model.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Durham, William McKinney

Advisor dc:contributor.advisor

• Ole Secher Madsen.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/38512

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/38512