Introduction to the research

When flow velocities at the seabed are very high, such as occur in storm conditions, sand is transported within a water-sediment mix, a few centimetres deep, moving over a flat, ripple-free bed. This sand transport regime is called “sheet-flow” and is important because of the high sand concentrations that are present in the sheet-low layer and very large volumes of sand are transported. Measurements of sheet-flow transport and transport processes, from controlled, large scale experiments, are essential for the development of well-founded predictive sand transport models.

The SANTOSS-project will, for the first time, bring together existing data from large-scale oscillatory sheet-flow experiments conducted in The Netherlands, the UK and elsewhere. The combined data will constitute the best possible set of existing large-scale experimental data for oscillatory sheet-flow conditions.

The research will also involve new experiments covering three important aspects of sheet-flow not covered by existing data:

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Velocities within the sheet-flow layer

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Flow acceleration effects on sheet-flow transport

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Effects of the wave-induced net currents and vertical orbital motions. These occur under real waves but are absent in flow tunnel experiments.

Analysis of the combined existing data, together with the results from the new experiments, will greatly extend present insight and understanding of sheet-flow dynamics. The results will be used in the project to:

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Test and develop semi-empirical sand transport formulae for sheet-flow conditions

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Establish best quantitative descriptions of concentrations, velocities and fluxes in sheet-flow

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Test and develop process-based numerical models of oscillatory sheet-flow