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  • An inventory of obstacles in rivers

    The goal of the ecological continuity project is to draw up an inventory of all obstacles blocking flows in all French rivers and to assess the degree to which those obstacles block the movement of species and sediment...

A map of continuities and discontinuities in France

A list of almost 50 000 obstacles, including dams, locks, weirs, mills no longer in operation, etc., on French rivers has been drawn up to date. They are the cause of major transformations in the morphology and hydrology of aquatic environments and have a profound negative impact on the operation of ecosystems. Impacts include damage to aquatic habitats, blocking the travel of migratory species and disturbing natural sedimentation processes.

With an array of partners, Onema is currently drawing up a list of obstacles.

"The goal is to assess the degree to which each obstacle blocks the movement of species and sediment", notes Jean-Marc Baudoin, an expert in aquatic habitats

."The inventory will identify the worst obstacles that will then receive priority status for modifications to effectively reduce ecological fragmentation". A national data base will centralise all information on the obstacles. One part of the data (national code, precise geographical coordinates, essential characteristics) will serve as the shared base for the various stakeholders in water issues and territorial planning. A second part comprising technical information required to determine the risks of ecological fragmentation will be reserved for stakeholders in restoration and policing activities. To calibrate the technical information, a national evaluation method on the capacity of species and sediment to overcome obstacles is currently being developed on the basis of experiments already carried out in the Loire-Bretagne basin.