Case study:Marsh restoration on the Merlue

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Location: 46° 30' 16", 5° 38' 7"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity
Country France
Main contact forename Eric
Main contact surname Chaput
Main contact user ID
Contact organisation Association pour le développement et l’animation de la Petite Montagne
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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The Merlue is a 7,9 km long tributary of the Valouse, with a small watershed (less than 15 km2) half covered by managed forests, half by non (or little) fertilized grassland. The fish population is mainly composed of two species : brown trout and bullhead (Cottus gobio). The invasive signal crayfish (Pacifastacus leniusculus) is also present. In its middle stretch, the Merlue used to cross a marsh, however more than one century ago, the riverbed was moved to the edge of the marsh in order to drain the land and plant softwood (which has never been productive). The new configuration affected the summer connection with the groundwater table. This explains both the frequency of drying up and the overheating of a portion of the river, two phenomena that are not observed downstream from the marsh, where the Merlue is in its original bed. In the lower stretch, the riverbed was enlarged by approximately five meters, resulting in shallow waters and reduced available habitat for aquatic wildlife. The Merlue is part of the Natura 2000 site “Petite montagne du Jura”. Restoration actions were carried out within the LIFE project “Ruisseaux de têtes de bassins et faune patrimoniale associée” (LIFE 04NAT/FR/000082), focusing on restoring the population of native white-clawed crayfish (Austropotamobius pallipes. Before the works , 19,4 hectares were acquired in the marsh, thanks to the intervention of the “property development and rural settlement society” ( SAFER) . Four hectares of invasive willows and undesirable tree species were removed. The old riverbed was found by infrared photography , since the analysis of land registers did not allow to locate it. The stream was moved where the former bed was and the rectified channel was filled. The new riverbed was only slightly excavated and was intentionally undersized (30 x 30 cm), so that it would naturally recreate its shape. Some ramps were was positioned under the bed where specific anthropogenic constraints (bridge, crossing for agricultural machinery , etc. ) did not allow a free dynamics. In the downstream portion, softwoods were removed . The riverbed of the Merlue was narrowed and raised by 50 cm adding sediments excavated in the nearby village (for the foundation of a house), and arranged in order to recreate a sinuous low-flow channel and a sequence of riffles and pools. The stretch ends with a drowned rock ramp, positioned at the same height as the current bottom of the riverbed .

Monitoring surveys and results

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The project allowed to increase by 300 m the stream length and to raise the water level along 1 500 m. Ten hectares of wetlands have been restored, which are also a relevant flood storage area. Habitats diversity and functionality were increased and initial monitoring results are encouraging, however it is too early to assess the biological gains of the operation.

Lessons learnt

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Image gallery


The Merlue just downstream the marsh in summer 2009. The bed moved [on the left] on the edge of the marsh [on the right] has been filled during the restoration works.
Uprooting and burning of willows present in the marsh during the summer of 2008.
The new riverbed slightly excavated.
The Merlue in the restored area during the winter 2008-2009. In the foreground, we can see a stone structure put in place in order to raise and narrow the riverbed.
First flood in autumn 2008 in the marsh, after its restoration.
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Catchment and subcatchment

Catchment

River basin district Rhône - Méditerranée
River basin Rhône-Mediterranean

Subcatchment

River name Merlue
Area category
Area (km2) 12
12 km²
1,200 ha
Maximum altitude category
Maximum altitude (m)
Dominant geology
Ecoregion Western Highlands
Dominant land cover Plantation forestry, Grassland
Waterbody ID



Site

Name Merlue
WFD water body codes FRDR493a
WFD (national) typology
WFD water body name
Pre-project morphology Single channel, Straight
Reference morphology Single channel, Sinuous, Pool-riffle
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 Groundwater
Dominant substrate Cobble, Gravel
River corridor land use
Average bankfull channel width category 2 - 5 m
Average bankfull channel width (m) 3
3 m
0.003 km
300 cm
Average bankfull channel depth category 0.5 - 2 m
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s) 1
1 m³/s
1,000 l/s
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m) 1450 m
1.45 km
145,000 cm
Project started 2008/07/01
Works started 2008/07/01
Works completed 2008/09/01
Project completed
Total cost category 100 - 500 k€
Total cost (k€) 136 k€
136,000 €
Benefit to cost ratio
Funding sources EU LIFE Programme

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design 24.5
24.5 k€
24,500 €
Parc naturel régional du Morvan, Office national de l’eau et des milieux aquatiques (Onema), université de Franche Comté.
Stakeholder engagement and communication
Works and works supervision 52
52 k€
52,000 €
Post-project management and maintenance
Monitoring

Supplementary funding information

26,000 € for land expropriation



Reasons for river restoration

Mitigation of a pressure
Hydromorphology Structure & condition of riparian zones, Width & depth variation
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor Restoration of riparian marshes
Planform / Channel pattern Channel widening
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
[[]] No No No No No

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
Invertebrates Yes No No No No

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


Monitoring documents



Additional documents and videos


Additional links and references

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Supplementary Information

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