Case study:Afon Clywdd

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Location: 53° 10' 58", -3° 22' 8"
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Project overview

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Status Planned
Project web site http://www.therrc.co.uk/sites/default/files/projects/40_afonclwyd.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 AECOM
Parent multi-site project
This is a parent project
encompassing the following
projects
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Project summary

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The Clwyd (Photo 1 and Map 1) is a large catchment in north-east Wales, discharging north into the Irish Sea. The confluence of the Afon Clwyd with the Afon Elwy is downstream of St Asaph, which in November 2012 was subject to severe flooding resulting in a fatality. The impact of flooding from the Afon Elwy, which flows through the town, was exacerbated by the backing up of flow at the confluence with the Afon Clwyd, which was also in spate. In 2015, Natural Resources Wales commissioned AECOM Consultants to identify potential Working with Natural Processes (WWNP) in the Elwy catchment which would provide climate resilience to the proposed improvements to engineered flood defences in St Asaph (AECOM Consultants 2015). Following the study, AECOM wanted to develop techniques for rapid assessment of WWNP that could be applied to different types of catchments. AECOM used EU innovation funding to test techniques in a number of catchments, including this study of potential WWNP in the Vale of Clwyd. A systematic review of the aerial imagery, Ordnance Survey (OS) mapping and flood zone/flood extent information was carried out to identify the most important morphological features in the catchment and to identify locations where the WWNP measures could potentially be implemented across the catchment. In contrast to the Elwy, the identification process included an assessment of implementation and shortlisting to streamline the process. The overall impact of the modelled WWNP is a reduction in peak flow and an increase in time-to-peak (TP). Peak flow reduction was approximately 6% for the 5-year design event and approximately 1% for the 200-year design event.

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Catchment and subcatchment



Site

Name Afon Clywdd
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Heavily modified water body No
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Protected species present No
Invasive species present No
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Project background

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Reasons for river restoration

Mitigation of a pressure Flood risk management
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Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Other Runoff pathway management
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Monitoring

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Supplementary Information

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