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Quantifying fluid retention due to natural vegetation in a forest floodplain analogue using the Aggregated Dead Zone (ADZ) dilution approach

Quantifying fluid retention due to natural vegetation in a forest floodplain analogue using the Aggregated Dead Zone (ADZ) dilution approach
Quantifying fluid retention due to natural vegetation in a forest floodplain analogue using the Aggregated Dead Zone (ADZ) dilution approach
Fluid retention and flow resistance due to natural vegetation remain poorly understood despite the importance of understanding these for flow routing and floodplain revegetation projects. Experiments were undertaken in a shallow earthen channel containing a natural cover of small trees, herbaceous plants and leaf-litter which were sequentially removed and subjected to a range of flows. A dilution monitoring approach within the Aggregated Dead Zone framework was applied to a series of floodplain vegetated flows, yielding information on bulk flow parameters including tracer dispersion, fluid retention and flow resistance at the reach-scale. The primary response of flow to vegetation removal was a small increase in bulk velocity, with depth and wetted width decreasing only slightly. Reach mean travel time and the advective time delay decreased by about a factor two with the removal of herbs, grass and leaf litter, leaving only trees. Removing the trees, leaving a bare earthen channel, only slightly decreased travel times. Flow resistance and retention exhibited large values for low discharge and converged on a constant low value for relatively high discharges. It is concluded that flow resistance during low flow is higher than in a high flow with the same vegetation. Consequently, sparse vegetation has a prominent effect on hydraulic retention compared with an unvegetated channel at low discharges but this becomes negligible during high discharges as momentum increasingly dominates the flow. This outcome casts doubt on the efficacy of scrubby vegetation to impede higher-velocity floodplain flows, showing need for field-scale determination of integral floodplain resistance.
0043-1397
Carling, Paul
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Leyland, Julian
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Kleinhans, Maarten G.
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Duranton, Pierre
be76f11f-b47f-4648-a253-e7ccf6be22ba
Besozzi, Louison
ef02adc5-94ca-42e7-b7ed-e1e3e6f1406c
Trieu, Hai Q
146d6771-1df6-449f-bce2-1e5529d8918a
Teske, Roy
d571d009-713a-4875-9bce-c1104de21c4c
Carling, Paul
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Leyland, Julian
6b1bb9b9-f3d5-4f40-8dd3-232139510e15
Kleinhans, Maarten G.
6620cb6f-d2b7-4f07-86c4-179e9d62c7ed
Duranton, Pierre
be76f11f-b47f-4648-a253-e7ccf6be22ba
Besozzi, Louison
ef02adc5-94ca-42e7-b7ed-e1e3e6f1406c
Trieu, Hai Q
146d6771-1df6-449f-bce2-1e5529d8918a
Teske, Roy
d571d009-713a-4875-9bce-c1104de21c4c

Carling, Paul, Leyland, Julian, Kleinhans, Maarten G., Duranton, Pierre, Besozzi, Louison, Trieu, Hai Q and Teske, Roy (2020) Quantifying fluid retention due to natural vegetation in a forest floodplain analogue using the Aggregated Dead Zone (ADZ) dilution approach. Water Resources Research.

Record type: Article

Abstract

Fluid retention and flow resistance due to natural vegetation remain poorly understood despite the importance of understanding these for flow routing and floodplain revegetation projects. Experiments were undertaken in a shallow earthen channel containing a natural cover of small trees, herbaceous plants and leaf-litter which were sequentially removed and subjected to a range of flows. A dilution monitoring approach within the Aggregated Dead Zone framework was applied to a series of floodplain vegetated flows, yielding information on bulk flow parameters including tracer dispersion, fluid retention and flow resistance at the reach-scale. The primary response of flow to vegetation removal was a small increase in bulk velocity, with depth and wetted width decreasing only slightly. Reach mean travel time and the advective time delay decreased by about a factor two with the removal of herbs, grass and leaf litter, leaving only trees. Removing the trees, leaving a bare earthen channel, only slightly decreased travel times. Flow resistance and retention exhibited large values for low discharge and converged on a constant low value for relatively high discharges. It is concluded that flow resistance during low flow is higher than in a high flow with the same vegetation. Consequently, sparse vegetation has a prominent effect on hydraulic retention compared with an unvegetated channel at low discharges but this becomes negligible during high discharges as momentum increasingly dominates the flow. This outcome casts doubt on the efficacy of scrubby vegetation to impede higher-velocity floodplain flows, showing need for field-scale determination of integral floodplain resistance.

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Accepted/In Press date: 19 June 2020
e-pub ahead of print date: 22 June 2020

Identifiers

Local EPrints ID: 442151
URI: http://eprints.soton.ac.uk/id/eprint/442151
ISSN: 0043-1397
PURE UUID: d3c3a99d-90b8-41d8-9ad6-e2a97635ee0d
ORCID for Julian Leyland: ORCID iD orcid.org/0000-0002-3419-9949

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Date deposited: 07 Jul 2020 16:55
Last modified: 18 Feb 2021 17:06

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