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

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Location: 46° 57' 51", 3° 55' 6"
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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


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.
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Catchment and subcatchment

Catchment

River basin district Loire-Bretagne
River basin

Subcatchment

River name Maria
Area category
Area (km2) 15
15 km²
1,500 ha
Maximum altitude category
Maximum altitude (m)
Dominant geology
Ecoregion Western Highlands
Dominant land cover Plantation forestry
Waterbody ID



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

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€) 10
10 k€
10,000 €
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 10
10 k€
10,000 €
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure Barriers to fish migration
Hydromorphology Continuity of sediment transport
Biology Fish
Physico-chemical
Other reasons for the project


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

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

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

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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