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A tale of two riffles: Using multidimensional, multifractional, time-varying sediment transport to assess self-maintenance in pool-riffle sequences

A tale of two riffles: Using multidimensional, multifractional, time-varying sediment transport to assess self-maintenance in pool-riffle sequences
A tale of two riffles: Using multidimensional, multifractional, time-varying sediment transport to assess self-maintenance in pool-riffle sequences
Pool-riffle sequences play a central role in providing habitat diversity conditions both in terms of flow and substrate in gravel bed streams. Understanding their capacity to self-maintain has been the focus of research for many years, starting with the velocity reversal hypothesis. This hypothesis relied only on cross sectional averaged flow information, but its limited success prompted extensions of the hypothesis and alternative explanations for self-maintenance. Significant advances beyond the velocity reversal hypothesis have been achieved by incorporating more information either on flow or sediment transport characteristics. However, this has been done in a compartmentalised way, with studies either focusing on one or the other aspect.

This work bridges the gap between these two aspects by using an approximate methodology that combines observed characteristic stage-dependent 3-D flow patterns with time-varying cross sectional information on bed shear stresses, sediment distribution and sediment bed changes during a one-year record of continuous discharges from a real stream. This methodology allows us to track the behaviour of different sediment size fractions along flow streamlines over time and identify self-maintenance conditions due to the combined effect of both flow multi-dimensionality and sediment transport.

We apply this approximate methodology to two contiguous pools and riffles and demonstrate that, unexpectedly, they may rely on different mechanisms for self-maintenance due to differences in geometry and sediment size distribution. We also demonstrate that our methodology is potentially overarching and integrative of previous partial approaches based on flow multidimensionality or sediment transport, which tend to underestimate the occurrence of self-maintenance. This article is protected by copyright. All rights reserved.
0043-1397
2095-2113
Bayat, Esmaeel
e1a86638-c1ed-4b03-93bf-85a897d88408
Rodriguez, Jose F.
a9546407-f4d7-44db-afbc-120d0d370625
Saco, Patricia M.
1d6e5edb-1aa1-4644-9c68-4aeaae16aeaf
de Almeida, Gustavo A. M.
f6edffc1-7bb3-443f-8829-e471b6514a7e
Vahidi, Elham
8e033b78-f40a-4f46-8e17-15ca12c5a27d
Garcia, Marcelo H.
a0b1434d-8951-4d4a-b992-18894e572d76
Bayat, Esmaeel
e1a86638-c1ed-4b03-93bf-85a897d88408
Rodriguez, Jose F.
a9546407-f4d7-44db-afbc-120d0d370625
Saco, Patricia M.
1d6e5edb-1aa1-4644-9c68-4aeaae16aeaf
de Almeida, Gustavo A. M.
f6edffc1-7bb3-443f-8829-e471b6514a7e
Vahidi, Elham
8e033b78-f40a-4f46-8e17-15ca12c5a27d
Garcia, Marcelo H.
a0b1434d-8951-4d4a-b992-18894e572d76

Bayat, Esmaeel, Rodriguez, Jose F., Saco, Patricia M., de Almeida, Gustavo A. M., Vahidi, Elham and Garcia, Marcelo H. (2017) A tale of two riffles: Using multidimensional, multifractional, time-varying sediment transport to assess self-maintenance in pool-riffle sequences. Water Resources Research, 53 (3), 2095-2113. (doi:10.1002/2016WR019464).

Record type: Article

Abstract

Pool-riffle sequences play a central role in providing habitat diversity conditions both in terms of flow and substrate in gravel bed streams. Understanding their capacity to self-maintain has been the focus of research for many years, starting with the velocity reversal hypothesis. This hypothesis relied only on cross sectional averaged flow information, but its limited success prompted extensions of the hypothesis and alternative explanations for self-maintenance. Significant advances beyond the velocity reversal hypothesis have been achieved by incorporating more information either on flow or sediment transport characteristics. However, this has been done in a compartmentalised way, with studies either focusing on one or the other aspect.

This work bridges the gap between these two aspects by using an approximate methodology that combines observed characteristic stage-dependent 3-D flow patterns with time-varying cross sectional information on bed shear stresses, sediment distribution and sediment bed changes during a one-year record of continuous discharges from a real stream. This methodology allows us to track the behaviour of different sediment size fractions along flow streamlines over time and identify self-maintenance conditions due to the combined effect of both flow multi-dimensionality and sediment transport.

We apply this approximate methodology to two contiguous pools and riffles and demonstrate that, unexpectedly, they may rely on different mechanisms for self-maintenance due to differences in geometry and sediment size distribution. We also demonstrate that our methodology is potentially overarching and integrative of previous partial approaches based on flow multidimensionality or sediment transport, which tend to underestimate the occurrence of self-maintenance. This article is protected by copyright. All rights reserved.

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Accepted/In Press date: 14 February 2017
e-pub ahead of print date: 13 March 2017
Published date: March 2017
Organisations: Water & Environmental Engineering Group

Identifiers

Local EPrints ID: 406341
URI: https://eprints.soton.ac.uk/id/eprint/406341
ISSN: 0043-1397
PURE UUID: 23a809ce-0485-4708-a326-23f40ec79303
ORCID for Gustavo A. M. de Almeida: ORCID iD orcid.org/0000-0002-3291-3985

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Date deposited: 10 Mar 2017 10:45
Last modified: 15 Aug 2019 05:03

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