Case study:River Ogwen and Nant Francon

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Location: 53° 7' 56.89" N, 4° 1' 53.96" W

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Project overview

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Status	Complete
Project web site
Themes	Fisheries, Flood risk management, Land use management - agriculture
Country	Wales
Main contact forename	Hugh
Main contact surname	Jones
Main contact user ID
Contact organisation	Natural Resources Wales
Contact organisation web site	http://naturalresourceswales.gov.uk/
Partner organisations	National Trust, Environment Agency
Parent multi-site project
This is a parent project encompassing the following projects	No

Restored bed level and bank profile following restoration (Nov 2012)

Project summary

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The Ogwen is in a mountainous location of Snowdonia below Llyn Ogwen (Lake Ogwen), and flows northwards through the Nant Ffrancon valley. During the 1960s the river was deepened by dredging over a 4km length downstream of the waterfall in an attempt to reduce the frequency of flooding over the valley floor to improve livestock grazing. Over the following 30 years the river flushed virtually all bed gravels through the system and scoured the river bed and banks. The reach became severely denuded of any stable habitat for flora and fauna, the once thriving salmon fishery declined and flooding was still troublesome to farmers. Four boulder cascades were created and pool and riffle sequences created in the upper reach. Some runs of gravel were introduced and shoals were created on the inside of bends. A major erosion site was reinstated using a willow mattress technique.

Monitoring surveys and results

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Lessons learnt

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Catchment and subcatchment

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Site

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Name	River Ogwen
WFD water body codes	GB110065054160
WFD (national) typology
WFD water body name
Pre-project morphology	Over deepened
Reference morphology	Pool-riffle
Desired post project morphology
Heavily modified water body	No
National/international site designation
Local/regional site designations
Protected species present	No
Invasive species present	No
Species of interest	Salmonids
Dominant hydrology
Dominant substrate	Gravel
River corridor land use	Agricultural (Livestock)
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

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Reach length directly affected (m)	900900 m <br />0.9 km <br />90,000 cm <br />
Project started	1998/09/01
Works started
Works completed	1998/11/30
Project completed
Total cost category	50 - 100 k€
Total cost (k€)	5656 k€ <br />56,000 € <br />
Benefit to cost ratio
Funding sources

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

Supplementary funding information

Of the £48,000 (€56,000) project cost- £8,000 (€9,300) was spent on a flood model and £5,000 (€5,800) was spent on design.

Reasons for river restoration

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Mitigation of a pressure	Flood risk management
Hydromorphology	Channel pattern/planform, sediment transport
Biology	Fish
Physico-chemical
Other reasons for the project

Measures

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Structural measures
Bank/bed modifications	Installation of cascades, Creation of pools and riffles
Floodplain / River corridor
Planform / Channel pattern	Morphology of the bed altered
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other

Monitoring

Hydromorphological quality elements

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quality elements

Element	When monitored		Type of monitoring		Control site used	Result
	Before measures	After measures	Qualitative	Quantitative

Biological quality elements

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quality elements

Element	When monitored		Type of monitoring		Control site used	Result
	Before measures	After measures	Qualitative	Quantitative
Fish	Yes	Yes	Yes	Yes	No	Improvement

Physico-chemical quality elements

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quality elements

Element	When monitored		Type of monitoring		Control site used	Result
	Before measures	After measures	Qualitative	Quantitative

Any other monitoring, e.g. social, economic

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Element	When monitored		Type of monitoring		Control site used	Result
	Before measures	After measures	Qualitative	Quantitative

Monitoring documents

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Image gallery

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Restored Island - Nov 2012

Restored section - Nov 2012

Additional documents and videos

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Additional links and references

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Link	Description
http://www.therrc.co.uk/pdf/manual/MAN 5 3.pdf	Manual of River Restoration Techniques entry (RRC)
http://www.therrc.co.uk/pdf/manual/MAN 8 4.pdf	Manual of River Restoration Techniques entry (RRC)

Supplementary Information

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