Case study:Reopening of the culverted Redon river

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Location: 46° 20' 16", 6° 25' 57"
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Project overview

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Status Complete
Project web site
Themes Environmental flows and water resources, Habitat and biodiversity
Country France
Main contact forename Maxime
Main contact surname Chateauvieux
Main contact user ID
Contact organisation Symasol
Contact organisation web site
Partner organisations Symasol, departmental environmental and agriculture division, the French National Agency for Water and Aquatic Environments (Office National de L’Eau et des Milieux Aquatiques), Fédération départementale de la pêche (departmental fishing federation), local fishing association, the commune.
Parent multi-site project
This is a parent project
encompassing the following
Reopening of 230 metres of the Redon. Overview of the site after restoration work -2009 (River next to parking lot) (Symasol).

Project summary

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1.5 km from its outlet, the Redon had been culverted for the purposes of a quarry. The passage of the river through a concrete culvert covering a 230 metre stretch prevents many of the fish from the lake from swimming upstream, to an ideal breeding ground. The quarry where the culvert is located is no longer active, therefore 230 metres of the culverted river were reopened. In order to diversify the environment, a meandering bed was created. Plantation was used to protect the banks and the longitudinal section was stabilised

Monitoring surveys and results

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Pre-restoration works monitoring have been carried out. It includes a topographic survey for a hydraulic analysis of the site. Furthermore, fish rescue by electric fishing was performed at the opening of the culvert.

Fish stocks were monitored following the culvert removal on the Redon, six months after the restoration work. As part of the appraisal of the “Crossborder river contractforthe southwest part of Lake Geneva” (2006-2012), fish stocks were monitored in all the watercourses in the area covered by the SYMASOL. For this, the fish population was counted in the Redon at the location of the work site in the summer of 2011, four years after the restoration work.

An IBGN survey was conducted in 2009 (two years after the work) by a consultancy.

Lake trout can now swim up the whole length of the Redon.

Six months after the works, about 230 river trout were recorded throughout the reopened stretch, i.e. 3,800 individuals per hectare against only fifteen or so individuals identified during the fish rescue operation.

The results of the 2011 electric fishing confirm the trend noted six months after work was completed. Thus, 48 trout were counted on the upstream station, i.e. 3,678 individuals per hectare.

These results are very positive and seem to indicate that the fish population is stabilising in the part of the watercourse where the culvert has been removed.

The IBGN analysis suggests that the quality of water is restrictive in this portion of the Redon. The taxon indicator (Hydropsychidae) is relatively tolerant to poor water quality and taxonomic diversity is quite low (18 taxons identified). However, the absence of a sampling point before the restoration work does not allow the observation of a potential gain in terms of water quality or habitat diversity due to removal of the culvert.

The outcome in terms of overall assessment is excellent from the point of view of elected officials, residents and fishing stakeholders.

Pursuant to the River Contract (2006-2012), a general policy to review weirs preventing river continuity was implemented. Rocky boulders or bypasses were set up to make weirs passable.

Lessons learnt

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Image gallery

Overview of the quarry before restoration work - 2007 (Symasol)
The Redon buried in the downstream section. Before restoration work -2007 (Symasol)
The Redon in the downstream section, 2 years after restoration work - 2009 (Symasol)
The Redon after the reopening and development of the low water channel - 2009 (Symasol)

Catchment and subcatchment


WFD water body codes FRDR11140
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present No
Species of interest river trout, lake trout
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category 2 - 5 m
Average bankfull channel width (m) 3
3 m
0.003 km
300 cm
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category 0.1 - 1.0 m³/s
Mean annual discharge (m3/s) 0.5
0.5 m³/s
500 l/s
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

Reach length directly affected (m) 230
230 m
0.23 km
23,000 cm
Project started 2006/09/01
Works started
Works completed
Project completed 2007/01/01
Total cost category 100 - 500 k€
Total cost (k€) 145
145 k€
145,000 €
Benefit to cost ratio
Funding sources Agence de l’eau (Water Agency) (31%), General Council (28%), Regional Council (10%), Symasol (31%).

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

Reasons for river restoration

Mitigation of a pressure
Hydromorphology Continuity for organisms
Biology Fish: Abundance
Other reasons for the project


Structural measures
Bank/bed modifications Reopening of culverted river, Bank stabilisation, Planting
Floodplain / River corridor
Planform / Channel pattern Meandering channel
Non-structural measures
Management interventions
Social measures (incl. engagement)


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

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 RedonGB.pdf All information on this page is copied from the AFB, The French Agency for biodiversity

Supplementary Information

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