Case study:Removal of the Cussy weir on the Maria stream

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Location: 46° 57' 51.30" N, 3° 55' 5.53" E

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Project overview

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Status	Complete
Project web site
Themes	Habitat and biodiversity, Hydromorphology
Country	France
Main contact forename	Laurent
Main contact surname	Paris
Main contact user ID
Contact organisation	Parc naturel régional du Morvan
Contact organisation web site	http://http://www.parcdumorvan.org/
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 Maria stream, a tributary of Dragne, is 10 Km long and presents very low anthropic alteration. Only a weir, 2 m high and 8 m wide, degrades the environment, constituting an obstacle to ecological continuity and sediment transport. It was built in 1932 to supply drinking water, but no longer used after 1951. A restoration project was undertaken. During the works, the river is diverted into a pipe. A straw filter is placed downstream of the structure to trap fine sediments. The work begins with the extraction of sediment upstream of the structure, placed on the sides. The weir is then destroyed and the banks stabilized with blocks, found on site.

Monitoring surveys and results

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The weir removal allows the reconnection of nine kilometers of waterways. The population composition has not changed after works: trout and sculpin remained the two species recorded. The 2004 monitoring shows a recolonization of upstream sector by trout fry. In 2009, the trout population increases and reaches its equilibrium level . In 2004, the lotic area recreated is immediately recolonized by sculpins. In 2009, Sculpin populations decrease. The evolution of the population of sculpin deserves a monitoring programme and comparisons with nearby rivers. The weir removal restores sediment transport. The vegetation naturally recolonize the environment and stabilize the banks. A new weir deletion on the Dragne watershed is planned for 2011.

Lessons learnt

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Image gallery

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The Cussy weir.

The Maria stream in October 2004, at the end of restoration works.

The Maria stream in 2004, few metres upstream of the removed weir. The banks are stabilized by blocks from the weir.

The Maria stream in 2009, five years after restoration.

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 Subcatchment River name Maria Area category Area (km2) 1515 km² <br />1,500 ha <br /> Maximum altitude category Maximum altitude (m) Dominant geology Ecoregion Western Highlands Dominant land cover Plantation forestry Waterbody ID Site Edit site Name Cussy WFD water body codes FRGR218 WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Parc naturel régional du Morvan Protected species present Yes Invasive species present No Species of interest trout, bullhead and white-clawed crayfish 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 Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started Works started 2004/10/01 Works completed 2004/10/31 Project completed Total cost category Total cost (k€) 1010 k€ <br />10,000 € <br /> Benefit to cost ratio Funding sources Agence de l’eau, direction régionale de l’environnement (DIREN). 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 1010 k€ <br />10,000 € <br /> Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Barriers to fish migration Hydromorphology Continuity of sediment transport Biology Fish Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Weir removal Floodplain / River corridor 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 Fish Yes Yes No No No 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