A numerical investigation into the importance of bed permeability on determining flow structures over river dunes

Research output: Contribution to journalArticle

Authors

Colleges, School and Institutes

External organisations

  • Durham University
  • Department of Geology and Department of Mechanical Science and Engineering; University of Illinois at Urbana-Champaign; Urbana Illinois USA

Abstract

Although permeable sediments dominate the majority of natural environments past work concerning bedform dynamics has considered the bed to be impermeable, and has generally neglected flow between the hyporheic zone and boundary layer. Herein, we present results detailing numerically modelled flow which allow the effects of bed permeability on bedform dynamics to be assessed.

Simulation of an isolated impermeable bedform over a permeable bed shows that flow is forced into the bed upstream of the dune and returns to the boundary layer at the leeside, in the form of returning jets that generate horseshoe-shaped vortices. The returning flow significantly influences the leeside flow, modifying the separation zone, lifting the shear layer adjoining the separation zone away from the bed. Simulation of a permeable dune on a permeable bed reveals even greater modifications as the flow through the dune negates the formation of any flow separation in the leeside. With two dunes placed in series the flow over the downstream dune is influenced by the developing boundary layer on the leeside of the upstream dune. For the permeable bed case the upwelling flow lifts the separated flow from the bed, modifies the shear layer through the coalescence with vortices generated, and causes the shear layer to undulate rather than be parallel to the bed.

These results demonstrate the significant effect that bed permeability has on the flow over bedforms that may be critical in affecting the flux of water and nutrients. This article is protected by copyright. All rights reserved.

Details

Original languageEnglish
JournalWater Resources Research
Early online date23 Mar 2017
Publication statusE-pub ahead of print - 23 Mar 2017