The University of Southampton
University of Southampton Institutional Repository

An experimental approach to characterising vegetation roughness in forested floodplains using dilution tracing and terrestrial laser scanning

An experimental approach to characterising vegetation roughness in forested floodplains using dilution tracing and terrestrial laser scanning
An experimental approach to characterising vegetation roughness in forested floodplains using dilution tracing and terrestrial laser scanning
The vegetation on forested floodplains plays an essential role in floodplain flow routing, flow dynamics and therefore the transfer of sediments and associated nutrients and contaminants. The flow resistance introduced by the presence of vegetation assemblages leads to changes in flow velocity and depth that, in turn, modulate sediment transport. Attempts to quantify these processes remain elusive due to difficulties in accurately estimating the altered flow parameters around and through vegetation. Here we employ complementary techniques of characterising the bulk flow properties and vegetation structure. Physical modelling of a prototype scale (2 x 45 m) shallow earthen channel containing small trees, herbaceous plants and leaf-litter was undertaken to explore the bulk flow characteristics. Vegetation structure and fluid retention was measured in controlled discharge experiments for: (1) natural cover of herbs and trees; (2) trees only and; (3) earthen channel only. Dilution-curve data were analysed within the Aggregated Dead Zone (ADZ) framework to yield bulk flow parameters including dispersion, fluid retention and flow resistance parameters. Vegetation structure is recorded using TLS, with data processed to represent vegetation structure as a 3D volume porous media. The main response of flow to vegetation removal was an increase in bulk velocity, with depth and wetted width decreasing slightly. Retentiveness was more prominent during low flow and all three experimental conditions tended to converge on a constant low value for high discharges. Reach mean travel times and the advective time delays decreased very slightly from experiments (1) to (2). The ADZ analysis and TLS data shows that in these two initial experiments, the trees provided the majority of the resistance in contrast to the aggregate effect of herbaceous plants and litter. Removing the trees further decreased travel times such that the ADZ residence time was more than halved moving from condition (1) to (3). The overall bulk flow effect of tree cover on retention is here expressed by the dispersive fraction parameter, which reduced from 0.4 to 0.2 when vegetation was removed.
Leyland, Julian
15cefd9f-2f5d-42a3-9d48-3e32c673ad41
Carling, Paul
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Kleinhans, Maarten G.
6620cb6f-d2b7-4f07-86c4-179e9d62c7ed
Vasilopoulos, Grigorios
300d6991-00cb-409a-9412-021eeb96fa49
Leyland, Julian
15cefd9f-2f5d-42a3-9d48-3e32c673ad41
Carling, Paul
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Kleinhans, Maarten G.
6620cb6f-d2b7-4f07-86c4-179e9d62c7ed
Vasilopoulos, Grigorios
300d6991-00cb-409a-9412-021eeb96fa49

Leyland, Julian, Carling, Paul, Kleinhans, Maarten G. and Vasilopoulos, Grigorios (2015) An experimental approach to characterising vegetation roughness in forested floodplains using dilution tracing and terrestrial laser scanning. American Geophysical Union, Fall Meeting 2015, United States. 14 - 18 Dec 2015.

Record type: Conference or Workshop Item (Paper)

Abstract

The vegetation on forested floodplains plays an essential role in floodplain flow routing, flow dynamics and therefore the transfer of sediments and associated nutrients and contaminants. The flow resistance introduced by the presence of vegetation assemblages leads to changes in flow velocity and depth that, in turn, modulate sediment transport. Attempts to quantify these processes remain elusive due to difficulties in accurately estimating the altered flow parameters around and through vegetation. Here we employ complementary techniques of characterising the bulk flow properties and vegetation structure. Physical modelling of a prototype scale (2 x 45 m) shallow earthen channel containing small trees, herbaceous plants and leaf-litter was undertaken to explore the bulk flow characteristics. Vegetation structure and fluid retention was measured in controlled discharge experiments for: (1) natural cover of herbs and trees; (2) trees only and; (3) earthen channel only. Dilution-curve data were analysed within the Aggregated Dead Zone (ADZ) framework to yield bulk flow parameters including dispersion, fluid retention and flow resistance parameters. Vegetation structure is recorded using TLS, with data processed to represent vegetation structure as a 3D volume porous media. The main response of flow to vegetation removal was an increase in bulk velocity, with depth and wetted width decreasing slightly. Retentiveness was more prominent during low flow and all three experimental conditions tended to converge on a constant low value for high discharges. Reach mean travel times and the advective time delays decreased very slightly from experiments (1) to (2). The ADZ analysis and TLS data shows that in these two initial experiments, the trees provided the majority of the resistance in contrast to the aggregate effect of herbaceous plants and litter. Removing the trees further decreased travel times such that the ADZ residence time was more than halved moving from condition (1) to (3). The overall bulk flow effect of tree cover on retention is here expressed by the dispersive fraction parameter, which reduced from 0.4 to 0.2 when vegetation was removed.

Full text not available from this repository.

More information

Published date: December 2015
Venue - Dates: American Geophysical Union, Fall Meeting 2015, United States, 2015-12-14 - 2015-12-18

Identifiers

Local EPrints ID: 432390
URI: http://eprints.soton.ac.uk/id/eprint/432390
PURE UUID: 5f096db7-f595-4af4-8e41-f88598765109

Catalogue record

Date deposited: 12 Jul 2019 16:30
Last modified: 12 May 2020 16:41

Export record

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.

×