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Accueil > Équipes > Equipe MEIGE : Modélisation, Expériences et Instrumentation pour la Géophysique et l’Environnement > Diffusion scientifique > Séminaires internes

Free surface effects on the morphology of river dunes and their evolution to upper stage plane beds

Suleyman Naqshband, 04/04/2013

A large number of bed form data from literature is analyzed, showing significantly different evolution of dune height and length in flows with low Froude numbers (negligible free surface effects) and flows with high Froude numbers (large free surface effects). For high Froude numbers, relative dune heights are observed to grow only in bed load dominant transport regime and start to decay for u*/ws (suspension number) exceeding 1. Dunes in this case are not observed for suspension numbers greater than 2.5. For low Froude numbers, relative dune heights continue to grow from bed load to suspended load dominant transport regime. Dunes in this case are not observed for suspension numbers greater than 5. We conclude that for reliable predictions of dune morphology and evolution to upper stage plane beds, it is essential to address both free surface effects and sediment transport mode. In addition, laboratory measurements are carried out to gain understanding in the processes leading to different dune height and length evolution under high and low Froude numbers.