Case study:Investigating the interaction between semi-natural floodplain woodland and flood flows at Great Triley Wood

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Location: 51° 51' 23", -3° 0' 0"
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Project overview

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Status Complete
Project web site http://www.therrc.co.uk/sites/default/files/projects/29_greattriley.pdf
Themes Flood risk management, Habitat and biodiversity, Land use management - forestry, Monitoring, Water quality
Country Wales
Main contact forename Huw
Main contact surname Thomas
Main contact user ID
Contact organisation Forest Research
Contact organisation web site http://www.forestresearch.gov.uk/
Partner organisations Natural Resources Wales, Woodland Trust
Parent multi-site project
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encompassing the following
projects
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Project summary

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The project was established as a research study to investigate how floodplain woodland affects flood flows. Great Triley Wood is a semi-natural, floodplain woodland owned and managed by the Woodland Trust. The site provided an opportunity to measure how trees, undergrowth and woody debris affect the hydraulic roughness of the floodplain and therefore the storage and passage of flood flows. Results are used to provide ‘hard’ evidence of how floodplain woodland impacts on flood risk and to help develop and test hydraulic models for wider application. Floodplain woodland dissipates flood energy, reducing flood velocity and increasing local water depths. This can reduce downstream flood peaks but increase upstream flooding due to the backing up of floodwaters. The formation of large woody dams has an important role to play in storing and deflecting flood flows. Individual dams can delay a 1% annual exceedance probability (AEP) event by 2–3 minutes.

Monitoring surveys and results

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Catchment and subcatchment



Site

Name Afon Einion
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Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation
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Protected species present No
Invasive species present No
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use
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Project background

Reach length directly affected (m)
Project started 2005
Works started
Works completed
Project completed
Total cost category
Total cost (k€) £160k
"£" is not declared as a valid unit of measurement for this property.
Benefit to cost ratio
Funding sources Forestry Commission, EU Interreg

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure Flood risk management
Hydromorphology
Biology
Physico-chemical
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Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor establishment of woodland
Planform / Channel pattern
Other
Non-structural measures
Management interventions
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Monitoring

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Monitoring documents



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Supplementary Information

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