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The impact of biological bedforms on near-bed and subsurface flow: a laboratory evaluated numerical study of flow in the vicinity of pits and mounds

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posted on 2019-07-02, 09:59 authored by Xu Han, Hongwei Fang, Matthew F. Johnson, Stephen Rice
The complex surface topography of river substrates controls near‐bed hydraulics and drives the exchange of subsurface and surface flow. In rivers, the topographic structures that are studied are usually formed by the flow but, it is known that many animals also create biogenic bedforms, such as pits and mounds. Here, a Large‐Eddy Simulation (LES) model of flow over a pit and a mound is evaluated with flume experiments. The model includes actual bedform topography, and the topographic complexity of the surrounding bed surface. Subsurface grains are organized in a body‐centered cubic packing arrangement. Model evaluation showed strong agreement between experimental and modelling results for velocity (R2 > 0.8) and good agreement for Reynolds stresses (R2 > 0.7), which is comparable to other similar studies. Simulation of the pit shows that the length of the downwelling region is smaller than the upwelling region and that the velocity magnitude is higher in the downwelling region. Simulation of the mound reveals that the flow is forced into the bed upstream of the mound and re‐emerges near the top of the mound. The recirculation zone is limited at the leeside of the mound. With increasing Reynolds number, the depth of the upwelling region at the leeside of the mound increases. The analysis of shear stress indicates that sediments on the upstream edge of the pit and on the downstream face of the mound are relatively unstable. These results demonstrate the effect of biogenic structures on the near‐bed flow field, hyporheic exchange, and sediment stability.

Funding

China Scholarship Council (CSC) (No. 201706210236)

History

School

  • Social Sciences

Department

  • Geography and Environment

Published in

Journal of Geophysical Research: Earth Surface

Volume

124

Issue

7

Pages

1939-1957

Citation

HAN, X. ... et al, 2019. The impact of biological bedforms on near-bed and subsurface flow: a laboratory evaluated numerical study of flow in the vicinity of pits and mounds. Journal of Geophysical Research: Earth Surface, doi:10.1029/2019JF005000.

Publisher

© American Geophysical Union

Version

  • VoR (Version of Record)

Publisher statement

An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union. HAN, X. ... et al, 2019. The impact of biological bedforms on near-bed and subsurface flow: a laboratory evaluated numerical study of flow in the vicinity of pits and mounds. Journal of Geophysical Research: Earth Surface, doi:10.1029/2019JF005000. To view the published open abstract, go to https://doi.org/10.1029/2019JF005000

Acceptance date

2019-06-24

Publication date

2019-07-01

Copyright date

2019

ISSN

2169-9011

eISSN

2169-9011

Language

  • en

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