MODEL TESTS ON LITTORAL SAND TRANSPORT RATE

This paper is an analysis of two sets of experimental results on littoral sand transport. A littoral sand transport expression is proposed, relating littoral transport rate to surf similarity parameter and hence to wave energy dissipation rate. The expression indicates that the "constant' in the CERC formula is dependent on the mobile bed beach slope and on the breaker index. The expression is also compared with some of the few published field measurements.

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Spectrally Resolved Energy Dissipation Rate and Momentum Flux of Breaking Waves

Journal of Physical Oceanography ◽

10.1175/2007jpo3762.1 ◽

2008 ◽

Vol 38 (6) ◽

pp. 1296-1312 ◽

Cited By ~ 77

Author(s):

Johannes R. Gemmrich ◽

Michael L. Banner ◽

Chris Garrett

Keyword(s):

Energy Dissipation ◽

Wave Field ◽

Wave Energy ◽

Dissipation Rate ◽

Momentum Flux ◽

Phase Speed ◽

Breaking Waves ◽

Energy Dissipation Rate ◽

Small Scale ◽

Breaking Wave

Abstract Video observations of the ocean surface taken from aboard the Research Platform FLIP reveal the distribution of the along-crest length and propagation velocity of breaking wave crests that generate visible whitecaps. The key quantity assessed is Λ(c)dc, the average length of breaking crests per unit area propagating with speeds in the range (c, c + dc). Independent of the wave field development, Λ(c) is found to peak at intermediate wave scales and to drop off sharply at larger and smaller scales. In developing seas breakers occur at a wide range of scales corresponding to phase speeds from about 0.1 cp to cp, where cp is the phase speed of the waves at the spectral peak. However, in developed seas, breaking is hardly observed at scales corresponding to phase speeds greater than 0.5 cp. The phase speed of the most frequent breakers shifts from 0.4 cp to 0.2 cp as the wave field develops. The occurrence of breakers at a particular scale as well as the rate of surface turnover are well correlated with the wave saturation. The fourth and fifth moments of Λ(c) are used to estimate breaking-wave-supported momentum fluxes, energy dissipation rate, and the fraction of momentum flux supported by air-entraining breaking waves. No indication of a Kolmogorov-type wave energy cascade was found; that is, there is no evidence that the wave energy dissipation is dominated by small-scale waves. The proportionality factor b linking breaking crest distributions to the energy dissipation rate is found to be (7 ± 3) × 10−5, much smaller than previous estimates.

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TOWARD AN IMPROVED EMPIRICAL FORMULA FOR LONGSHORE SAND TRANSPORT

Coastal Engineering Proceedings ◽

10.9753/icce.v21.88 ◽

1988 ◽

Vol 1 (21) ◽

pp. 88 ◽

Cited By ~ 3

Author(s):

Nicholas C. Kraus ◽

Kathryn J. Gingerich ◽

Julie Dean Rosati

Keyword(s):

Oscillatory Flow ◽

Field Experiments ◽

Surf Zone ◽

Transport Rate ◽

Sand Transport ◽

Longshore Current ◽

Wave Energy Dissipation ◽

Total Transport ◽

Local Wave ◽

Correction Terms

This paper presents results of two field experiments performed using portable traps to obtain point measurements of the longshore sand transport rate in the surf zone. The magnitude of the transport rate per unit width of surf zone is found to depend on the product of the local wave height and mean longshore current speed, but correlation is much improved by including two correction terms, one accounting for local wave energy dissipation and the other for the fluctuation in the longshore current. The field transport rates are also found to be compatible with laboratory rates obtained under combined unidirectional and oscillatory flow. Total transport rates previously reported for this experiment program are revised with recently determined sand trapping efficiencies.

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