Case study:River Ogwen and Nant Francon

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Location: 53° 7' 57", -4° 1' 54"
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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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Image gallery


Restored Island - Nov 2012
Restored section - Nov 2012
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Catchment and subcatchment

Catchment

River basin district Western Wales
River basin North West Wales

Subcatchment

River name Ogwen - upper
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 1000 - 2000 m
Maximum altitude (m) 1036
1,036 m
1.036 km
103,600 cm
Dominant geology Siliceous
Ecoregion Great Britain
Dominant land cover Acid Grassland
Waterbody ID GB110065054160



Site

Name River Ogwen
WFD water body codes GB110065054160
WFD (national) typology
WFD water body name Ogwen - upper
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

Reach length directly affected (m) 900
900 m
0.9 km
90,000 cm
Project started 1998/09/01
Works started
Works completed 1998/11/30
Project completed
Total cost category 50 - 100 k€
Total cost (k€) 56
56 k€
56,000 €
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

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


Measures

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

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

Biological 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

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

Any other monitoring, e.g. social, economic

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


Monitoring documents



Additional documents and videos


Additional links and references

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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