Case study:Restoration of the longitudinal continuity along the Canche and its classified tributaries

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Location: 50° 29' 33.60" N, 1° 42' 43.97" E

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Project overview

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Status	Complete
Project web site
Themes	Habitat and biodiversity, Monitoring, Water quality
Country	France
Main contact forename	Herve
Main contact surname	Regniez
Main contact user ID
Contact organisation	Syndicat mixte pour le SAGE de la Canche
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

A weir after restoration of the river bed.

Project summary

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The Canche is a small 90 kilometers long river, which sources are at Gouy-en-Ternois , at an altitude of 135 m. It flows into the English Channel 20 km north of the Somme bay. Its watershed is mainly composed of meadows and wooded areas. The majority of tributaries (Ternoise , Planquette, Créquoise Bras de Bronne, Course, Dordogne and Huitrepin) lie on its right side. These rivers offer a variety of habitats suitable for spawning and development of migratory fish. They still host salmon, sea trout, eel, river lamprey (Lampetra fluviatilis) and sea lamprey (Petromyzon marinus). The Canche has been classified as "migratory fish watercourse" since 1986 , and its tributaries have been since 1997. However, the Canche basin presents many barriers to flow and fish migration. 151 structures were identified and 77 are impassable by migratory fish. These are weirs of former flour mills, or for irrigation, or sluices. In addition to their effects on blocking fish migration, these barriers contribute to the degradation of aquatic habitats. Streams classified by the prefect, under Article L.432 -6 of the Environmental Code, had to ensure continuity for fish within a period of five years after the publication of the decree. The departmental angling federation started in 1999 the implementation of measures to make some barriers compliant. At the end of 2002 , the “syndicat mixte pour le SAGE de la Canche" (grouping of local administrations having the responsibility to implement the Canche basin plan) to take a specific jurisdiction to ensure the project management of removal or improvement of barriers along the Canche and its tributaries. These new statutes allow the union to trigger several removal operations, following a list of priorities defined in the 2005. After identifying the owners and upstream/ downstream stakeholders , meetings were held with the water police and Onema to inform residents and owners on their rights and obligations. The organization of field visits identified uses, management approaches, physical condition, historical , tourism and economic value of the structures . For each of them, a comprehensive analysis allowed to define the type of measures to be implemented. So far, twenty structures without economic interest were tackled by the restoration measures. Most of them consisted in dismantling sluices. When the remaining sill was still an impassable obstacle even without the sluices, additional works, e.g. fish passes, were made. In some cases, restoration of the riverbed was carried out, particularly when the riverbed had been displaced.

Monitoring surveys and results

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The actions carried out so far have increased the potential recolonization lenght by migratory fish by 2.5 km in the Course, 2.8 km in the Baillons stream, 3 km in the Créquoise and several kilometers in the Ternoise.

Lessons learnt

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Image gallery

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The Canche at Conchy-sur-Canche before dismantling of the sluice.

The Canche at Conchy-sur-Canche after dismantling of the sluice. The banks made ​​bare by the lowering of the water line were quickly vegetated.

A weir on the Créquoise at Lebiez before restoration of the river bed.

A weir on the Créquoise at Lebiez after restoration of the river bed. After restoration, the threshold becomes passable for trout, eels and lampreys.

The sluice of Wavrans-sur-Ternoise after works: opening valves and fish pass.

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Canche River basin Artois-Picardie Subcatchment River name Canche Area category 1000 - 10000 km² Area (km2) Maximum altitude category 100 - 200 m Maximum altitude (m) Dominant geology Siliceous Ecoregion Western Plains Dominant land cover Extensive agriculture, Grassland, Woodland Waterbody ID Site Edit site Name Canche WFD water body codes FRAR13 WFD (national) typology WFD water body name Pre-project morphology Single channel, Straight Reference morphology Single channel, Sinuous, Step-pool 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 Quick run-off, Groundwater Dominant substrate Gravel, Cobble River corridor land use Extensive agriculture, Woodland, Grassland Average bankfull channel width category 5 - 10 m Average bankfull channel width (m) Average bankfull channel depth category 0.5 - 2 m Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) 1111 m³/s <br />11,000 l/s <br /> Average channel gradient category Average channel gradient 1.5 Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started 2006/01/01 Works started Works completed Project completed Total cost category Total cost (k€) 265265 k€ <br />265,000 € <br /> Benefit to cost ratio Funding sources Water Agency, Department of fisheries, Syndicat mixte pour le SAGE de la Canche Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Syndicat mixte pour le SAGE de la Canche Stakeholder engagement and communication Syndicat mixte pour le SAGE de la Canche Works and works supervision Syndicat mixte pour le SAGE de la Canche Post-project management and maintenance Syndicat mixte pour le SAGE de la Canche Monitoring Syndicat mixte pour le SAGE de la Canche Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Continuity for organisms, Continuity of sediment transport, Quantity & dynamics of flow, Flow velocities Biology Fish: Species composition, Fish: Abundance, Fish: Disturbance-sensitive species Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Removal of obstructions to flow Floodplain / River corridor Planform / Channel pattern Creation of fish passes 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: Species composition Yes Improvement Fish: Abundance Fish: Disturbance-sensitive species 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