Case study:Reopening of the culverted Redon river

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Location: 46° 20' 16.49" N, 6° 25' 56.88" E

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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	http://www.symasol.fr/
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 projects	No

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 The quarry where the culvert is located is no longer active, therefore 230 metres of the culverted river were reopened.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

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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 Select a catchment/subcatchment Site Edit site Name 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) 33 m <br />0.003 km <br />300 cm <br /> Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category 0.1 - 1.0 m³/s Mean annual discharge (m3/s) 0.50.5 m³/s <br />500 l/s <br /> Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 230230 m <br />0.23 km <br />23,000 cm <br /> Project started 2006/09/01 Works started Works completed Project completed 2007/01/01 Total cost category 100 - 500 k€ Total cost (k€) 145145 k€ <br />145,000 € <br /> 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 Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit 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 Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information