Case study:Nant Barrog

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Location: 53° 11' 58", -3° 36' 58"
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Project overview

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Status In progress
Project web site http://www.therrc.co.uk/sites/default/files/projects/41_nantbarrog.pdf
Themes Flood risk management, Habitat and biodiversity, Land use management - agriculture, Land use management - forestry, Water quality
Country Wales
Main contact forename Jacques
Main contact surname Sisson
Main contact user ID
Contact organisation Natural Resources Wales
Contact organisation web site http://naturalresources.wales/?lang=en
Partner organisations Coed Cymru, Bangor University, Woodland Trust
Parent multi-site project
This is a parent project
encompassing the following
projects
No
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Project summary

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In 2012, the city of St Asaph – located on a downstream reach of the Afon Elwy (Map 1) – suffered severe flooding which resulted in a fatality. Natural Resources Wales began an investigation into how traditional hard engineered approaches, such as those proposed for the St Asaph flood alleviation scheme, could be supported by Working with Natural Processes (WWNP) measures. The investigation also looked at how these measures could have multiple ecosystem benefits. Llanfair Talhaiarn is a small village in the Elwy catchment, located at the confluence of Nant Barrog with the main river Elwy. The Nant Barrog is conveyed beneath the main street to the Elwy through the Water Street culvert. In periods of high rainfall the culvert is overwhelmed, resulting in flooding of properties in the village. Natural Resources Wales is reviewing the refurbishment of the culvert. WWNP measures recommended for the Barrog in the Elwy Natural Flood Risk Management and Ecosystem Services Study (2015) were further reviewed at the subcatchment scale. WWNP measures for the Nant Barrog catchment were recommended in the Llanfair Talhaiarn Natural Flood Management Study (2015). A revision of the shortlisted options was further reviewed as part of the Llanfair Talhaiarn project appraisal report (2016) and the cost benefits of the different options were considered. The resulting recommended WWNP measures are listed in Table 1.. Coed Cymru, in partnership with Natural Resources Wales, the Woodland Trust and other organisations, will submit a bid in 2017 to the Welsh Government Rural Development Plan Sustainable Management Scheme for funding to implement the measures recommended in the Llanfair Talhaiarn report. The Water Street culvert has an inlet capacity of 4.2m3s-1. Flooding will occur at a return period of a 1 in 50 year event with a peak flow of 4.8m3s-1. Modelling of 4 WWNP packages showed that, when considered separately, sufficient reductions would occur during the 1 in 50 year event for flow to remain within the channel at the culvert.

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Catchment and subcatchment



Site

Name Nant Barrog
WFD water body codes
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WFD water body name
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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
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River corridor land use
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Project background

Reach length directly affected (m)
Project started 2017
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Funding sources Rural Development Plan Sustainable Management Scheme

Cost for project phases

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Reasons for river restoration

Mitigation of a pressure Flood risk management
Hydromorphology
Biology
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Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Other Runoff pathway management
Non-structural measures
Management interventions
Social measures (incl. engagement)
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Monitoring

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Supplementary Information

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