Case study:Removal of the Coupeau impoundment on Vicoin River and riverbed restoration

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Location: 48° 3' 48", -0° 49' 44"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity, Hydromorphology, Social benefits
Country France
Main contact forename Évelyne
Main contact surname AVRIL
Main contact user ID
Contact organisation Mairie de Saint-Berthevin
Contact organisation web site
Partner organisations
Parent multi-site project
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encompassing the following
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Project summary

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A lot of works are present on the Vicoin River. One of these is the weir of the Coupeau impoundment, realized in 1969. This pond, closed by a weir 9 meters large and 1,80 meters high, covers three hectares, 800 m long and 40 m wide at maximum. This impoundment hasn’t a flow regulation reason; instead it is relationed with a lot of recreational activities, such as restaurant, camping, fishing and walking. The weir affects the ecological continuity and the sediment transport. The impoundment is eutrophic and a typological modification in fish population is observed. The site needs frequent mechanical digging of sediment and the volumes extracted become each time bigger. After the three last sediment removals, in 1988 for 15 000 m3, in 1996 with 8 000 m3 and in 2004 pour with 30 000 m3 (110 000 €), an alternative site management analysis is undertook. After the sediment removal in 2004, during several months the weir has been left open allowing the river to recreate a preferential channel. In 2008, the weir is removed. The riverbed is reshaped respecting the new natural channel. A 4 meters riverbed on average (2 meters in low water) is created, as well as outflow wetland flooded during high water events. Some works on banks (especially bioengineering), are realized. Also touristic and recreational facilities, such as trails and footbridge, will be constructed on the entire site in 2010.

Monitoring surveys and results

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Image gallery

The coupeau impoundment.
The Coupeau weir
The retention area during the 2005 winter. A new river channel is created and vegetation developped.
Riverbad recreation works.
The Vicoin river, after restoration, in April 2009.

Catchment and subcatchment


River basin district Loire-Bretagne
River basin Loire


River name Vicoin
Area category
Area (km2)
Maximum altitude category
Maximum altitude (m)
Dominant geology
Ecoregion Western Plains
Dominant land cover Intensive agriculture (arable)
Waterbody ID


Name Coupeau (Saint-Berthevin)
WFD water body codes FRGR0517
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 No
Invasive species present No
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use Intensive agriculture (arable)
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) 800
800 m
0.8 km
80,000 cm
Project started 2004/06/01
Works started 2008/06/01
Works completed 2010/12/01
Project completed
Total cost category
Total cost (k€) 521,065
521,065 k€
521,065,000 €
Benefit to cost ratio
Funding sources Agence de l’eau (40 %), conseil général (13 %), conseil régional (6 %), syndicat du bassin du Vicoin (1 %), ministère de l’intérieur (pour les aménagements récréatifs et touristiques) (6 %).

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design 61
61 k€
61,000 €
Office national de l’eau et des milieux aquatiques (Onema) - service départemental, direction régionale de l’environnement (DIREN), direction départementale de l’agriculture et des forêts (DDAF), fédération départementale de la pêche.
Stakeholder engagement and communication
Works and works supervision 443
443 k€
443,000 €
Post-project management and maintenance 16
16 k€
16,000 €

Reasons for river restoration

Mitigation of a pressure Impoundments (not hydropower)
Hydromorphology Continuity of sediment transport
Biology Fish: Species composition
Other reasons for the project


Structural measures
Bank/bed modifications Weir removal, Barrier removal, Riverbed restoration
Floodplain / River corridor Creation of wetland
Planform / Channel pattern Creation of new channel
Other construction of recreational facilities (trails and footbridges)
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
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Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
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Any other monitoring, e.g. social, economic

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Before measures After measures Qualitative Quantitative

Monitoring documents

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Additional links and references

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Supplementary Information

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