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Influence of sand supply and grain size on upper regime bedforms
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  • Sydney Sanders,
  • Sadegh Jafarinik,
  • Ricardo Hernández Moreira,
  • Ryan Johnson,
  • Amanda Balkus,
  • Mahsa Ahmadpoor,
  • Brandon Fryson,
  • Briana McQueen,
  • Juan Jose Fedele,
  • Enrica Viparelli
Sydney Sanders
University of South Carolina
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Sadegh Jafarinik
Unknown
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Ricardo Hernández Moreira
University of South Carolina
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Ryan Johnson
University of South Carolina
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Amanda Balkus
University of South Carolina
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Mahsa Ahmadpoor
University of South Carolina
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Brandon Fryson
University of South Carolina
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Briana McQueen
University of South Carolina
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Juan Jose Fedele
Exxon Mobil
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Enrica Viparelli
University of South Carolina

Corresponding Author:[email protected]

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Abstract

Notwithstanding the large number of studies on bedforms such as dunes and antidunes, performing quantitative predictions of bedform type and geometry remains an open problem. Here we present the results of laboratory experiments specifically designed to study how sediment supply and caliber may impact equilibrium bedform type and geometry in the upper regime. Experiments were performed in a sediment feed flume with flow rates varying between 5 l/s and 30 l/s, sand supply rates varying between 0.6 kg/min and 20 kg/min, uniform and non-uniform sediment grain sizes with geometric mean diameter varying between 0.22 mm and 0.87 mm. The experimental data and the comparison with datasets available in the literature revealed that the ratio of the volume transport of sediment to the volume transport of water Qs/Qw plays a prime control on the equilibrium bed configuration. The equilibrium bed configuration transitions from washed out dunes (lower regime), to downstream migrating antidunes (upper regime) for Qs/Qw between 0.0003 and 0.0007. For values of Qs/Qw greater than those typical of downstream migrating antidunes, the bedform wavelength increases with Qs/Qw. At these high values of Qs/Qw equilibrium bed configurations with fine sand are characterized by upstream migrating antidunes or cyclic steps, and significant suspended load. In experiments with coarse sand, equilibrium is characterized by plane bed with bedload transport in sheet flow mode. Standing waves form at the transition between downstream migrating antidunes and bed configurations with upstream migrating bedforms.