Case study:Marsh restoration on the Merlue

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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
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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.

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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 Subcatchment River name Hake Area category 10 - 100 km² Area (km2) 15 km²1,500 ha <br /> Maximum altitude category 200 - 500 m Maximum altitude (m) Dominant geology Siliceous Ecoregion Western Highlands Dominant land cover Waterbody ID Site Edit 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) 33 m <br />0.003 km <br />300 cm <br /> Average bankfull channel depth category 0.5 - 2 m Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) 11 m³/s <br />1,000 l/s <br /> Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 1450 m1.45 km <br />145,000 cm <br /> 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 € <br /> Benefit to cost ratio Funding sources LIFE Streams Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Structure & condition of riparian zones, Width & depth variation Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Increase in bed width Floodplain / River corridor Restoration of riparian marshes 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 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 Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information