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Session B1: Fish-Friendly Management of First Dams in the Tidal Area of the Gironde Estuary (France, SW)
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Abstract
Abstract The particular case of the first dams met by the European eel migrating in the tidal area of the Gironde estuary is examined here. For these obstacles, typological elements are proposed, based on the nature of the hydraulic dams, but also on that of its downstream and upstream areas. Various technical tries are already performed to minimize impact of these dams, in tidal areas. These obstacles exist to prevent and limit entrance of salt or brackish water in the swamp and to prevent floods. Glass eel and tidal and marine young species colonize theses areas carried by the stream. The actually management of these dams doesn’t permit to the different species to go upstream because the dams are closed only 5 minutes after the flow inversion. The good management of these dams would allow the colonization of 37% of the space in the tributary or the swamp. Since 2009, MIGADO Association, in collaboration with local users, tries to manage the dams with different systems adapted to the user needs and to the natural characteristics of the swamp. The tests consist in installing : · holds to prevent the closure of the tidal dams, · stiffeners (« raidisseurs ») to slow down the closure of the tidal dams, · optimized management of the present gate on the tidal dams, · telescopic gate allowing to keep a upstream water level defined. The evaluation shows promising results, answering to users’ needs upstream (none floods), a management adapted to the needs, and increase of fish population in the swamp and tributary (multiplied density by 20). There is no impact of suspension material entry in the middle. All system can be adapted to each swamp and to user needs. This system, little expensive and autonomous, allows to glass eel to colonize swamp and tributaries in the tidal area.
Type
event
event
event
Date
2015-06-22