Effect of bed permeability and hyporheic flow on turbulent flow over bed forms

Research output: Contribution to journalArticle

Authors

Colleges, School and Institutes

External organisations

  • Departments of Geology, Geography and Geographic Information Science, Mechanical Science and Engineering and Ven Te Chow Hydrosystems Laboratory; University of Illinois at Urbana-Champaign; Illinois; USA
  • Department of Geography and Geographic Information Science; University of Illinois at Urbana-Champaign; Illinois; USA
  • Department of Geology and Department of Mechanical Science and Engineering; University of Illinois at Urbana-Champaign; Urbana Illinois USA
  • Durham University

Abstract

This paper uses particle imaging velocimetry to provide the first measurements detailing the flow field over a porous bed in the presence of bed forms. The results demonstrate that flow downstream of coarse-grained bed forms on permeable beds is fundamentally different to that over impermeable beds. Most significantly, the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface, such that reattachment of the separated flow does not occur and the Reynolds stresses bounding the separation zone are substantially lessened. These results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bed forms. Water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers, yet mass and momentum exchanges across the bed interface are not routinely incorporated into flow models. Our observations suggest that ignoring such exchange processes in coarse-grained rivers may overlook important implications. These new results also provide insight to explain the distinctive morphology of coarse-grained bed forms, the production of openwork textures in gravels, and the absence of ripples in coarse sands, all of which have implications for modeling and prediction of sediment entrainment and flow resistance.

Details

Original languageEnglish
Pages (from-to)6435-6442
JournalGeophysical Research Letters
Volume41
Issue number18
Early online date26 Sep 2014
Publication statusPublished - 28 Sep 2014

Keywords

  • bed forms, permeability, turbulence, hyporheic flow, coarse sediments, morphodynamics