Case study:Removal of the Stalapos weir over the river Alagnon

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Location: 45° 6' 8.83" N, 2° 51' 55.74" E

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Project overview

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Status	Complete
Project web site
Themes	Fisheries, Habitat and biodiversity, Hydromorphology
Country	France
Main contact forename	Guillaume
Main contact surname	Ponsonnaille
Main contact user ID
Contact organisation	Syndicat intercommunal de gestion de l’Alagnon et de ses affluents (SIGAL)
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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Between the municipalities of Murat and Albepierre-Bredons the biological and morphological continuity of river Alagnon was interrupted by a weir for the water supply of a mill. The intake structure was 2,7 m high and 26,5 m wide. A fish pass with limited funcionality hindered the fish migration. On the left bank there is a campsite and meadows on the right. The restoration of the fish continuity of the Alagnon is one of the main objectives of the River Alagnon 2001-2007 contract, supported by the Syndicat Intercommunal de Gestion de l’ALagnon (SIGAL). The weir wasn’t used anymore and in 2008 the removal works begun, the riverbed was terraced and bank protections were put in place to prevent bank erosion at the campsite side. The banks were reshaped and revegeteted. After the works were completed morphological adjustments have already been observed (in the work area, the riverbed is lowered by 1.1 m which seems to be close to equilibrium). At 260 m downstream, at the Stalapos bridge, deposits of materials cause an elevation close to 60 cm. At the railway bridge (360 m upstream of the work) and 800 meters downstream of the weir removed no significant effect was observed. The first counts of spawning trout show a decrease in the work area; instead, an increase is observed upstream. The immediate impact of the work on trout populations are already canceled by the extremely rapid recolonization upstream.

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Image gallery

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The Stalapos weir in january 2008, before the removal works

The Stalapos weir removal in june 2008, during the works. In this phase the stream flow was deverted.

View on the weir before removal works

View of the weir after removal works: the riverbanks is partially revegeteted and the riverbad is diversified.

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Loire-Bretagne River basin Loire Subcatchment River name Alagnon Area category Area (km2) 10441,044 km² <br />104,400 ha <br /> Maximum altitude category Maximum altitude (m) Dominant geology Ecoregion Western Highlands Dominant land cover Waterbody ID Site Edit site Name Stalapos (Murat) WFD water body codes FRGR0247 WFD (national) typology WFD water body name L'Alagnon et ses affluents depuis la source jusqu'a sa confluence avec l'Allanche Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Parc naturel régional des Volcans d’Auvergne Protected species present No Invasive species present No Species of interest Dominant hydrology Dominant substrate River corridor land use 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 Edit project background Reach length directly affected (m) 400400 m <br />0.4 km <br />40,000 cm <br /> Project started Works started 2008/06/01 Works completed 2009/11/01 Project completed Total cost category Total cost (k€) 173173 k€ <br />173,000 € <br /> Benefit to cost ratio Funding sources Agence de l’eau (40 %), conseil général (25%), conseil régional (15%), syndicat mixte de gestion de l’Alagnon (10%), fédération départementale de la pêche (10%). Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design 1010 k€ <br />10,000 € <br /> Office national de l’eau et des milieux aquatiques (Onema), fédération départementale de la pêche Stakeholder engagement and communication Works and works supervision 153153 k€ <br />153,000 € <br /> Post-project management and maintenance Monitoring bureau d’études et fedération départementale de la pêche Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Barriers to fish migration Hydromorphology Continuity for organisms Biology Continuity for fish Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Bank improvement, Weir removal, Bed reprofiling, Riverbank revegetation 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 Fish Yes Yes No Yes No Awaiting results 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 Case study description by ONEMA (French National Agency for Water and Aquatic Environments) (in French) article on Journal of the Loire-Bretagne Water Agency Additional links and references Edit links and references Link Description http://www.eau-loire-bretagne.fr/les rendez-vous de leau/trophees de leau/trophees 2009/Tr09 Sigal.pdf Lauréat le syndicat interdépartemental de gestion de l’Alagnon et de ses affluents Supplementary Information Edit Supplementary Information