Case study:Langonnet river

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Location: 48° 5' 33.92" N, 3° 30' 18.48" W

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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	Yohann
Main contact surname	FUENTES
Main contact user ID
Contact organisation	(FORECASTER)
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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Over the years, heavy hydraulic works were carried out on the Lagonnet River, such as straightening and widening of the river course, causing habitat depletion and lowering of the water table. The main goals of the restoration activity were to restore the morphology and functionality of the river and to improve the habitat diversification. A preliminary assessment, carried out in 2001, has defined the technical goals: to improve the longitudinal and cross section profile diversification, to define a narrower flow section (especially in low water) and a sequence of riffles and pools. The reactivation of the river dynamics allow to keep the restoration results on the long term. The works included the installation of 24 sills and 239 groynes (in blocks or wooden). Berms are also created along 250 m and blocks are put in place on the riverbed. The maintenance of 2687 m of riparian forest and new plantation along 1400 m of river banks were carried on.

Monitoring surveys and results

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Lessons learnt

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Image gallery

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Examples of intervention on the Lagonnet river.

Blocks put in place on the Lagonnet river bed.

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 Langonnet Area category 10 - 100 km² Area (km2) 34 km²3,400 ha <br /> Maximum altitude category 100 - 200 m Maximum altitude (m) Dominant geology Siliceous Ecoregion Central Plains Dominant land cover Waterbody ID Site Edit site Name Langonnet River WFD water body codes FRJ471400A WFD (national) typology HER1-12 / HER2-60 WFD water body name Pre-project morphology Single channel, Straight Reference morphology Single channel, Sinuous 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 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 0.005117 Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 5300 m5.3 km <br />530,000 cm <br /> Project started 2000/01/01 Works started 2004/01/01 Works completed 2006/01/01 Project completed Total cost category more than 10000 k€ Total cost (k€) 150.315150.315 k€ <br />150,315 € <br /> Benefit to cost ratio Funding sources l'Etat et la Région (Volet "Milieux aquatiques et poissons migrateurs" CPER 2000-2006), l'Agence de l'Eau Loire-Bretagne (50%), la Région Bretagne (15%), le Conseil Général du Morbihan (15%) et les Pêcheurs (20%). Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Fishermen (20%) Yohann Fuentes Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring 1 - 10 k€ FDPPMA 56. Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Channel pattern/planform, Quantity & dynamics of flow, Width & depth variation Biology Fish: Species composition Physico-chemical Temperature Other reasons for the project Landscape enhancement Measures Edit Measures Structural measures Bank/bed modifications Creation of pools and riffles, Creation of groynes, introduction of blocks, Creation of berms Floodplain / River corridor Develop riparian forest, Tree plantation 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 Channel pattern/planform Yes Yes 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 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 Temperature Yes Yes Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Case study description (in French) Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information