Case study:Restoration of the previous riverbed of the Dadon

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Location: 45° 51' 4.09" N, 5° 57' 51.33" E

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Project overview

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Status	Complete
Project web site
Themes	Habitat and biodiversity, Hydromorphology, Monitoring, Water quality
Country	France
Main contact forename	Regis
Main contact surname	Talguen
Main contact user ID
Contact organisation	Syndicat mixte interdépartemental d’aménagement du Chéran
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

A few months after restoration

Project summary

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The Dadon is one of the last free flowing tributaries of the Lower Cheran. The Dadon watershed is concerned with two areas of industrial activities ( Alby -sur- Cheran and Rumilly) on its downstream sector, the rest of the watershed is occupied by farm land (55 % of the area ) and forest (13 % ).

The main pressure factors on the Dadon are the following:

• accidental pollutant releases in the industrial areas;
• organic pollution from farms and food processing factories;
• over-widening, straightening and embankment of its course, causing habitat depletion and lowering of the water table in its downstream stretch.

These factors greatly reduced the initially existing connections between the Dadon and the Cheran, thereby significantly lowering the ecological value of this naturally rich confluence area.

The main goals of the project were to restore the original riverbed of the Dadon, and to diversify flows and habitats, especially increasing water depths at low water flows. It was also aimed to stabilize banks and restore riparian vegetation. The works consisted of three steps:

• 2004 (involved length 350 m): rock sills and groynes to promote diversification of habitats; construction of vegetated log cribwalls, associated with geotextile to ensure bank stabilization (the restoration of a natural lateral dynamics was not part of project goals); creation of a narrower and meandering river bed;
• 2006 (involved length 475 m, downstream the previous stretch): the stream is returned in its original sinuous bed, as it was before the 90’s;
• 2009 (involved length 175 m, further downstream): introduction of blocks, stone sills, wooden groynes.

The works were carried out within the framework of the river contract brought by the Syndicat Mixte Interdépartemental d’Aménagement du Chéran (SMIAC). The local angling association strongly supported the action.

Monitoring surveys and results

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The first results of the post-work monitoring are in overall terms encouraging. An improvement of the quality of habitats and of the macro-benthic population was demonstrated. The fish population shows some improvement, although the goal to restore a structured trout population is not yet met. From a social point of view, the operation was very well accepted.

Lessons learnt

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Image gallery

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The Dadon riverbed, before restoration, in June 2004.

The riverbed after restoration, in August 2004: it recovered its meandering channel.

The rectifed river channel, before restoration, in June 2004.

The The meandering riverbed after restoration, in August 2

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Rhône - Méditerranée River basin Haute-Savoie Subcatchment River name Dadon Area category 100 - 1000 km² Area (km2) Maximum altitude category 500 - 1000 m Maximum altitude (m) Dominant geology Siliceous Ecoregion Western Highlands Dominant land cover Waterbody ID Site Edit site Name Dadon WFD water body codes FRDR11706 WFD (national) typology WFD water body name Pre-project morphology Single channel, Straight Reference morphology Single channel, Sinuous Desired post project morphology Heavily modified water body true National/international site designation Local/regional site designations Protected species present Invasive species present Species of interest Dominant hydrology Quick run-off Dominant substrate Bedrock, Cobble, Gravel River corridor land use Extensive agriculture, Grassland Average bankfull channel width category 5 - 10 m Average bankfull channel width (m) Average bankfull channel depth category 2 - 5 m Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) 0.90.9 m³/s <br />900 l/s <br /> Average channel gradient category Average channel gradient 0.25 Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 1000 m1 km <br />100,000 cm <br /> Project started 2004/05/01 Works started 2004/05/01 Works completed 2009/09/01 Project completed Total cost category Total cost (k€) 195195 k€ <br />195,000 € <br /> Benefit to cost ratio Funding sources Water Agency, SMIAC, Councils of Savoie and Haute-Savoie Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design 1 - 10 k€ Water Agency Stakeholder engagement and communication Water Agency Works and works supervision 182.62182.62 k€ <br />182,620 € <br /> Water Agency Post-project management and maintenance 44 k€ <br />4,000 € <br /> Water Agency Monitoring Water Agency Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Riparian development Hydromorphology Width & depth variation, Flow velocities, Quantity & dynamics of flow, Channel pattern/planform, Continuity for organisms Biology Fish: Species composition, Fish: Abundance Physico-chemical Other reasons for the project Bank erosion, Landscape enhancement Measures Edit Measures Structural measures Bank/bed modifications Implementation of rip rap, Habitat diversification, Implementation of vegetated boxes, Depth variation, Riverbed restoration Floodplain / River corridor Planform / Channel pattern Creation of meanders, Adding sinuosity 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 Width & depth variation Yes Yes Yes Improvement Channel pattern/planform Yes Yes Yes Improvement Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Fish: Species composition Yes Yes Yes Improvement Fish: Abundance Yes Yes Yes Improvement 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) Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information