The University of Southampton
University of Southampton Institutional Repository

Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment

Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment
Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment
The time-averaged and instantaneous flow velocity structures of flood waters are not well understood for irregular surfaces such as are created by the presence of roots and fallen branches on forested floodplains. Natural flow structures commonly depart systematically from those described for idealised roughness elements, and an important knowledge gap exists surrounding the effects of natural flow structures on vertical exchanges of fluid and momentum. An improved understanding of the flow structure is required to model flows over forested floodplains more accurately, and to distinguish their dynamics from non-vegetated floodplains or indeed floodplains with other vegetation types, such as reed or grass. Here we present a quantification of the three-dimensional structure of mean flow velocity and turbulence as measured under controlled conditions in an experimental flume using a physical reproduction of a patch of forested floodplain. The results conform in part to existing models of local flow structure over simple roughness elements in aspects such as flow separation downstream of protruding roots, flow reattachment, and the lowering of the velocity maximum further downstream. However, the irregular shape of the surface of the floodplain with exposed roots causes the three-dimensional flow structure to deviate from that anticipated based on previous studies of flows over idealised two-dimensional roughness elements. The results emphasise varied effects of inheritance of flow structures that are generated upstream—the local response of the flow to similar obstacles depends on their spatial organisation and larger-scale context. Key differences from idealised models include the absence of a fully-developed flow at any location in the test section, and various interactions of flow structures such as a reduction of flow separation due to cross-stream circulation and the diversion of the flow over and around the irregular shapes of the roots.
1932-6203
Reesink, Arnold
e9a3724d-3430-4fad-b85e-b27ed7343e53
Darby, Stephen
4c3e1c76-d404-4ff3-86f8-84e42fbb7970
Sear, David
ccd892ab-a93d-4073-a11c-b8bca42ecfd3
Leyland, Julian
6b1bb9b9-f3d5-4f40-8dd3-232139510e15
Morgan, Peter
c8f71e7a-8eca-4036-b6b9-e7f5b1a58e70
Richardson, Keith
73f2c32d-43b7-43da-b15d-8b11368d7221
Brasington, James
bed2c201-e84a-461d-bcc6-4c8d952da803
Reesink, Arnold
e9a3724d-3430-4fad-b85e-b27ed7343e53
Darby, Stephen
4c3e1c76-d404-4ff3-86f8-84e42fbb7970
Sear, David
ccd892ab-a93d-4073-a11c-b8bca42ecfd3
Leyland, Julian
6b1bb9b9-f3d5-4f40-8dd3-232139510e15
Morgan, Peter
c8f71e7a-8eca-4036-b6b9-e7f5b1a58e70
Richardson, Keith
73f2c32d-43b7-43da-b15d-8b11368d7221
Brasington, James
bed2c201-e84a-461d-bcc6-4c8d952da803

Reesink, Arnold, Darby, Stephen, Sear, David, Leyland, Julian, Morgan, Peter, Richardson, Keith and Brasington, James (2020) Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment. PLoS ONE, 15 (2), [e0229306]. (doi:10.1371/journal.pone.0229306).

Record type: Article

Abstract

The time-averaged and instantaneous flow velocity structures of flood waters are not well understood for irregular surfaces such as are created by the presence of roots and fallen branches on forested floodplains. Natural flow structures commonly depart systematically from those described for idealised roughness elements, and an important knowledge gap exists surrounding the effects of natural flow structures on vertical exchanges of fluid and momentum. An improved understanding of the flow structure is required to model flows over forested floodplains more accurately, and to distinguish their dynamics from non-vegetated floodplains or indeed floodplains with other vegetation types, such as reed or grass. Here we present a quantification of the three-dimensional structure of mean flow velocity and turbulence as measured under controlled conditions in an experimental flume using a physical reproduction of a patch of forested floodplain. The results conform in part to existing models of local flow structure over simple roughness elements in aspects such as flow separation downstream of protruding roots, flow reattachment, and the lowering of the velocity maximum further downstream. However, the irregular shape of the surface of the floodplain with exposed roots causes the three-dimensional flow structure to deviate from that anticipated based on previous studies of flows over idealised two-dimensional roughness elements. The results emphasise varied effects of inheritance of flow structures that are generated upstream—the local response of the flow to similar obstacles depends on their spatial organisation and larger-scale context. Key differences from idealised models include the absence of a fully-developed flow at any location in the test section, and various interactions of flow structures such as a reduction of flow separation due to cross-stream circulation and the diversion of the flow over and around the irregular shapes of the roots.

Text
journal.pone.0229306 - Version of Record
Available under License Creative Commons Attribution.
Download (5MB)

More information

Accepted/In Press date: 3 February 2020
Published date: 26 February 2020

Identifiers

Local EPrints ID: 438411
URI: http://eprints.soton.ac.uk/id/eprint/438411
ISSN: 1932-6203
PURE UUID: 89b6a9a3-d5a9-4ab8-8de0-86b9595be40b
ORCID for Stephen Darby: ORCID iD orcid.org/0000-0001-8778-4394
ORCID for David Sear: ORCID iD orcid.org/0000-0003-0191-6179
ORCID for Julian Leyland: ORCID iD orcid.org/0000-0002-3419-9949

Catalogue record

Date deposited: 09 Mar 2020 17:32
Last modified: 18 Feb 2021 17:06

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×