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Longshore sediment transport rate calculated incorporating wave orbital velocity fluctuationsSmith, Ernest Ray 30 October 2006 (has links)
Laboratory experiments were performed to study and improve longshore sediment
transport rate predictions. Measured total longshore transport in the laboratory was
approximately three times greater for plunging breakers than spilling breakers. Three
distinct zones of longshore transport were observed across the surf zone: the incipient
breaker zone, inner surf zone, and swash zone. Transport at incipient breaking was
influenced by breaker type; inner surf zone transport was dominated by wave height,
independent of wave period; and swash zone transport was dependent on wave period.
Selected predictive formulas to compute total load and distributed load transport
were compared to laboratory and field data. Equations by Kamphuis (1991) and Madsen
et al. (2003) gave consistent total sediment transport estimates for both laboratory and
field data. Additionally, the CERC formula predicted measurements well if calibrated
and applied to similar breaker types. Each of the distributed load models had
shortcomings. The energetics model of Bodge and Dean (1987) was sensitive to
fluctuations in energy dissipation and often predicted transport peaks that were not
present in the data. The Watanabe (1992) equation, based on time-averaged bottom stress, predicted no transport at most laboratory locations. The Van Rijn (1993) model
was comprehensive and required hydrodynamic, bedform, and sediment data. The
model estimated the laboratory cross-shore distribution well, but greatly overestimated
field transport.
Seven models were developed in this study based on the principle that transported
sediment is mobilized by the total shear stress acting on the bottom and transported by
the current at that location. Shear stress, including the turbulent component, was
calculated from the wave orbital velocity. Models 1 through 3 gave good estimates of
the transport distribution, but underpredicted the transport peak near the plunging wave
breakpoint. A suspension term was included in Models 4 through 7, which improved
estimates near breaking for plunging breakers. Models 4, 5 and 7 also compared well to
the field measurements.
It was concluded that breaker type is an important variable in determining the
amount of transport that occurs at a location. Lastly, inclusion of the turbulent
component of the orbital velocity is vital in predictive sediment transport equations.
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Limts Of Beach And Dune Erosion In Response To Wave Runup From Large-Scale Laboratroy DataRoberts, Tiffany M 30 April 2008 (has links)
The SUPERTANK dataset is analyzed to examine the upper limit of beach change in response to elevated water level induced by wave runup. Thirty SUPERTANK runs are investigated, including both erosional and accretionary wave conditions under random and monochromatic waves. Two experiments, one under a spilling and one under a plunging breaker-type, from the Large-Scale Sediment Transport Facility (LSTF) are also analyzed. The upper limit of beach change approximately equals the maximum vertical excursion of swash runup. Exceptions to this direct relationship are those with beach or dune scarps when gravity-driven changes, i.e., avalanching, become significant. The vertical extent of wave runup, Rmax, above mean water level on a beach without a scarp is found to approximately equal the significant breaking wave height, Hbs. Therefore, a simple formula Rmax = Hbs is proposed. The linear relationship between maximum runup and breaking wave height is supported by a conceptual derivation. This predictive formula reproduced the measured runup from a large-scale 3-dimensional movable bed physical model. Beach and dune scarps substantially limit the uprush of swash motion, resulting in a much reduced maximum runup. Predictions of wave runup are not improved by including a slope-dependent surf-similarity parameter. The limit of wave runup is substantially less for monochromatic waves than for random waves, attributed to absence of low-frequency motion for monochromatic waves.
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