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.

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The Colostre canalised before restoration (1999).

One of the Colostre meanders (2009).

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) 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 Edit site 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 Edit project background 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 Edit reasons for restoration 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 Edit Measures Structural measures Bank/bed modifications Weir removal 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 meeting Other River contract 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: Species composition Yes Yes Yes Improvement Macrophytes & phytobenthos: Taxonomic composition Yes 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 Presence of beavers Yes Improvement 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). Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information