Nearshore sediment transport: Coupling sand tracer dynamics with oceanographic forcing

作者：Bosnic I^*; Cascalho J; Taborda R; Drago T; Herminio J; Rosa M; Dias J; Garel E

来源：Marine Geology, 2017, 385: 293-303.

DOI：10.1016/j.margeo.2017.02.004

• Sediment dynamics
• Remobilization
• Bottom boundary layer
• Depth of closure

The understanding of the sedimentary links between the beach and the continental shelf is crucial for the evaluation of the coastal sediment budget. However, the comprehension of this dynamics is still poorly understood owing greatly to the lack of direct sediment transport measurement at seasonal and longer time scales. This work aims at evaluating sediment transport just seaward of the closure depth through a sand tracer experiment coupled with wave-current monitoring and modelling. Observations were carried out over 1 year at 14 m depth over a sandy continental shelf offshore Tavira (southern Portugal). The sand tracer experiment was carried out by injecting 400 kg of fluorescent tracer followed by four sediment sampling surveys. Tracer results show a high dispersion of the tracer cloud with a net transport of low magnitude. Time-averaged alongshelf sediment transport rate was estimated in 0.61 m(3)/m/yr (southwestward) while the cross-shelf transport rate was estimated in 0.31 m(3)/m/yr (onshore). During the observational period nearbed currents were dominated by the northeastern component, thus flowing in the opposite direction of the tracer displacement. However, when wave-current bed shear stress exceeded the threshold of particle motion, nearbed currents were dominated by a southwestern component which is compatible with tracer displacement. Overall this study showed that seaward the closure depth bottom sediment dynamics is characterized by frequent remobilization but with very low net transport rates.

• 出版日期2017-3-1