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| Titel |
Bedforms induced by solitary waves: laboratory studies on generation and migration rate |
| VerfasserIn |
Giovanni la Forgia, Claudia Adduce, Federico Falcini, Chris Paola |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148835
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| Publikation (Nr.) |
 EGU/EGU2017-13128.pdf |
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| Zusammenfassung |
| This study presents experiments on the formation of sandy bedforms, produced by surface
solitary waves (SSWs) in shallow water conditions. The experiments were carried out in a
12.0 m long, 0.15 m wide and 0.5 m high flume, at Saint Anthony Falls Laboratory in
Minneapolis. The tank is filled by fresh water and a removable gate, placed at the left
hand-side of the tank, divides the flume in two regions: the lock region and the ambient fluid
region. The standard lock-release method generates SSWs by producing a displacement
between the free surfaces that are divided by the gate. Wave amplitude, wavelength, and
celerity depend on the lock length and on the water level difference between the two regions.
Natural sand particles (D50=0.64) are arranged on the bottom in order to form a horizontal
flat layer with a thickness of 2 cm. A digital pressure gauge and a high-resolution acoustic
velocimeter allowed us to measure, locally, both pressure and 3D water velocity induced on
the bottom by each wave. Image analysis technique is then used to obtain the main
wave features: amplitude, wavelength, and celerity. Dye is finally used as vertical
tracer to mark the horizontal speed induced by the wave. For each experiment we
generated 400 waves, having the same features and we analyzed their action on sand
particles placed on the bottom. The stroke, induced by each wave, entails a shear
stress on the sand particles, causing sediment transport in the direction of wave
propagation. Immediately after the wave passage, a back flow occurs near the bottom. The
horizontal pressure gradient and the velocity field induced by the wave cause the
boundary layer separation and the consequent reverse flow. Depending on the wave
features and on the water depth, the boundary shear stress induced by the reverse
flow can exceed the critical value inducing the back motion of the sand particles.
The experiments show that the particle back motion is localized at particular cross
sections along the tank, where the wave steepening occur. For this reason, the pressure
and velocity measures were collected in several cross sections along the tank. The
propagation of consecutive waves with the same features induces the generation
of erosion and accumulation zones, which slowly evolve in isometric bedforms. |
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