Home - Themes - Diagnose physical alterations in rivers - Restoring ecological continuity


    -Didier Louis \ EPTB Charente
    "Efforts to preserve the eel in the Charente basin are an important policy for EPTB Charente..."

    -Jacques Pulou \ FNE (FRAPNA)
    "In 2008, the status report for the Rhône- Méditerranée river-basin management plan (RBMP) revealed a surprisingly high number of water bodies that will not achieve good status due to hydromorphological disturbances and obstacles to ecological continuity..."

    -Marc Papinutti \ VNF
    "Ecological continuity is a major issue for VNF. We must reconcile the development of our 6 700 kilometres of waterways with efforts to reduce our impact, notably concerning ecological continuity..."

Restoring ecological continuity

Throughout France, Onema personnel have worked hard in favour of ecological continuity and provided local projects with their technical know-how. Below are a few examples of the work in 2012.

Opening the marches in the Charente estuary to glass eels

Since 2010, R&D work has been undertaken on tide gates in the Charente estuary in the framework of the eelmanagement plan. The work was managed by the Onema-Irstea-IMFT Ecohydraulic centre, in conjunction with the Onema local office and an array of partners, namely the Charente-Maritime departmental council, EBTP Charente, Charente-Maritime fishing federation and UNIMA (Charente-Maritime union of marsh managers). The goal was to find technical solutions to restore the free movement of young eels. More precisely, the project targeted systems to maintain the tide gates partially open, thus enabling rising tides to carry the glass eels beyond the gates and into the marshes. The trials were carried out during 47 rising tides on two sites, the Charras canal and the Biard lock. The results demonstrated the biological effectiveness of the systems in that over 60 kg and 100 kg of glass eels recolonized the marches upstream of the two sites in just a single season. The entering quantities of seawater produced no notable impact in terms of either increased salinity in the canals or risks of overflow. These results will serve to set up balanced management systems to assist the eel populations.

Contact :

A concerted effort to restore ecological continuity in the Ariège river

The restoration of ecological continuity is a priority issue in the Ariège river basin. The Ariège, a Natura 2000 tributary to the Garonne river, is a sizeable river and very important for the reproduction of Atlantic salmon. It is also highly developed with 11 hydroelectric dams that are difficult obstacles for migratory fish. Since 2012, there has been a concerted effort to restore the migration of fish. The project involves the hydroelectric operators in the Ariège department organised in a professional association (ASL Rivière Ariège), Onema, the Adour-Garonne Water agency, the Midi-Pyrénées environmental agency, Migado, the Ariège fishing federation and engineering firms. The project was triggered by the police inspections in 2010 on the downstream-passage systems carried out by the Onema Ariège and Haute-Garonne local offices. The inspections resulted in mediation whereby the owners of installations (local governments, individuals) committed to upgrading their systems. Thanks to financial aid from the Water agency and technical support from the partners, six of the eight Ariège dams should be equipped with a new system by the end of 2014. For example, fish-friendly screens were installed at the Saverdun dam at the end of 2012. There is hope for restoration of free movement of fish along the entire Ariège river if the hydroelectric operators in the Haute- Garonne department join the ASL professional association in 2013 as planned.

Reconciling agriculture and ecological continuity in the Digeanne river

The Digeanne river in the Côte d’Or department is a biological reserve, but has suffered alterations to its morphology and breaks in its ecological continuity. At the old Essarois forges, the installations no longer function, but continue to affect the biological operation of the river by cutting its length in half, slowing the flow of water and blocking the movement of fish and sediment. In 2011, the owner, a farmer who wanted to set up a fish farm, contacted Onema and the Chatillonais river board. A project to reinstall the river in its original talweg and eliminate an obstacle to continuity gradually emerged, making it possible to meet the needs of the owner and achieve an ambitious physical restoration of the riverbed. The operation was carried out by the owner with technical support from the river board and the specific knowledge available from the Onema Côted’Or local office and Bourgogne France- Comté regional office. Once all the regulatory procedures had been accomplished, the river was returned to its original bed over a distance of 1 500 metres, the lateral reaches were filled in and the obstacle along the former dike was replaced with a wider installation to improve ecological continuity. This project succeeded thanks to the owner’s desire to make it work and the effective cooperation between the various participants. Ecological monitoring has since been initiated in conjunction with Onema and the Côte d’Or fishing federation.

Contact :