Case study:Refilling the meanders of the Colostre

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Location: 43° 47' 59.23" N, 6° 2' 28.12" E

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Project overview

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Status	Complete
Project web site
Themes
Country	France
Main contact forename	Vincent
Main contact surname	Duru
Main contact user ID
Contact organisation	FDPPMA Alpes-de-Haute-Provence
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 Colostre, a tributary of the River Verdon, is a typically Mediterranean river, with very low water levels upstream of Riez and flash flooding due to storms. The Colostre constitutes one of the only breeding grounds for brown trout. The beaver has also been recorded in this area. In the 1960s, following exceptional summer flooding, hydraulic improvements were made in order to modify the longitudinal profile of the river (resizing, straightening of the river and creation of weirs). These developments degraded the habitats of the river and caused significant erosion of the river banks. In response to this situation, in 1996, state fishing institutes and the local fishing association, initiated a protection Plan with the aim of free movement of salmonids and rediversification of habitats. The restoration measures formed part of the implementation of this plan. Thirteen meanders were restored. The disconnected meanders had not been filled in and instead had been left uncultivated; most of them thus remained identifiable. The first stage consisted of restoring access to the meanders by removing the poplars planted during the resizing of the river. Next, the current was diverted towards the old meanders which remained visible. The entrance to the straight channel was blocked using a submersible weir (consisted of timber billets covered with gravels, geotextile and protective mesh). The downstream part of the straight section was not closed off in order to allow for the dispersal of floodwaters. In areas in which the meanders were not identified, various experimental habitat diversification developments were carried out and weirs were removed or modified.

Monitoring surveys and results

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Lessons learnt

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Catchment and subcatchment

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Catchment

River basin district	Alpes-de-Haute-Provence
River basin	Rhône-Mediterranean

Subcatchment

River name	Colostre
Area category	100 - 1000 km²
Area (km2)	215 km²21,500 ha <br />
Maximum altitude category
Maximum altitude (m)
Dominant geology
Ecoregion	Alps
Dominant land cover
Waterbody ID

Site

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Name	Regional Natural Park of Verdon
WFD water body codes	FRDR251
WFD (national) typology
WFD water body name
Pre-project morphology	Single channel, Straight
Reference morphology	Sinuous
Desired post project morphology
Heavily modified water body	true
National/international site designation	EU - Special Protected Area
Local/regional site designations
Protected species present
Invasive species present
Species of interest
Dominant hydrology	Quick run-off, Artificially regulated
Dominant substrate
River corridor land use
Average bankfull channel width category	2 - 5 m
Average bankfull channel width (m)	44 m <br />0.004 km <br />400 cm <br />
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)	0.670.67 m³/s <br />670 l/s <br />
Average channel gradient category
Average channel gradient	1e-005
Average unit stream power (W/m2)	0.0164267250.0164 W/m² <br />

Project background

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Reach length directly affected (m)	11000 m11 km <br />1,100,000 cm <br />
Project started	1996/01/01
Works started	1999/01/01
Works completed	2001/01/01
Project completed
Total cost category	50 - 100 k€
Total cost (k€)	66 k€66,000 € <br />
Benefit to cost ratio
Funding sources	Water Agency, Regional Council, Dèpartment-level Council, Higher Fishing Council, Local fishing associations

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	50 - 100 k€	66 k€66,000 € <br />	Conseil Supérior de la Pêche-Departmental Brigade
Post-project management and maintenance			Conseil Général (Départment Level Council)
Monitoring			Conseil Supérior de la Pêche-Departmental Brigade

Reasons for river restoration

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Mitigation of a pressure
Hydromorphology	Continuity for organisms, Continuity of sediment transport, Width & depth variation, Structure & condition of riparian zones, Channel pattern/planform
Biology	Fish: Abundance, Fish: Disturbance-sensitive species
Physico-chemical
Other reasons for the project

Measures

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Structural measures
Bank/bed modifications	Removal of weirs
Floodplain / River corridor
Planform / Channel pattern	Removal of poplars in old meanders, Re-meandering
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)	Agreement with the owners, Public meetings in each commun affected by the project
Other	River contract

Monitoring

Hydromorphological quality elements

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quality elements

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

Biological quality elements

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quality elements

Element	When monitored		Type of monitoring		Control site used	Result
	Before measures	After measures	Qualitative	Quantitative
Fish: Species composition	Yes	Yes		Yes		Improvement
Macrophytes & phytobenthos: Taxonomic composition		Yes				Improvement

Physico-chemical quality elements

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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

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

Monitoring documents

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Image gallery

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The Colostre canalised before restoration (1999).

One of the Colostre meanders (2009).

Additional documents and videos

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Additional links and references

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Link	Description

Supplementary Information

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