Case study:Langonnet river

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Location: 48° 5' 34", -3° 30' 18"
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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
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encompassing the following
projects
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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


Examples of intervention on the Lagonnet river.
Blocks put in place on the Lagonnet river bed.
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Catchment and subcatchment

Catchment

River basin district Loire-Bretagne
River basin Loire

Subcatchment

River name Langonnet
Area category 10 - 100 km²
Area (km2) 34 km²
3,400 ha
Maximum altitude category 100 - 200 m
Maximum altitude (m)
Dominant geology Siliceous
Ecoregion Central Plains
Dominant land cover
Waterbody ID



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

Reach length directly affected (m) 5300 m
5.3 km
530,000 cm
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€) 150.315
150.315 k€
150,315 €
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

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

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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Channel pattern/planform Yes Yes

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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Temperature Yes Yes


Monitoring documents



Additional documents and videos


Additional links and references

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Supplementary Information

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