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Adaptative management of hydraulic structures on the Sèvre nantaise and Thouet rivers

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The Sèvre nantaise and the Thouet are tributaries of the River Loire. The Sèvre nantaise flows over 159 kilometres and drains a catchment area of 2,356 km². The Thouet is 159 kilometres long and drains a catchment area of 3,452 km². Both catchments are situated in 2 Regions, pays de la Loire and Poitou charentes in the west of France. Development of a multicriteria tool and approach to develop intervention programmes for river restoration. 300 sites have undergone the participative multicriteria analysis. 3 programmes of opening of gates and lowering of structures have already been conducted.

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Removal of 20 small structures and diversification of the main chanel on the river Couasnon

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The Couasnon flows 39.6 km before it reaches the Authion river.  The 14 km upstream of Greater Baugé are classified as first category water (very good status), while the rest of the stream is classified second category. Many infrastructures have been built in the river in the 70/80s. These obstacles have an impact on the hydraulic nature of the Couasnon. Twenty-seven valves and five dispatchers have been installed for agricultural purposes, and these infrastuctures add to the negative impact the  eleven existing mills already add on the hydromorphology of the river. As a consequence, the water quality has decreased and the habitat has been affected. In addition, structures prevent the free movement of fish, causing siltation of the water course, resulting in the proliferation of plant water and the rise of the water temperature. Hence, it was decided to remove the 20 hydraulic structures affecting the quality of the river.

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Removal of the Kernansquillec dam over the river Léguer

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The dam was situated on River Léguer, a 58 km river which flows in the English Channel. Removal of a 15 m tall dam (built in 1920) to improve the continuity and to enhance fish migration potential. Enhancement of the public safety (dam started to crack)

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Removal of the Maisons-Rouges dam over the river Vienne

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The solution was implemented on the river Vienne, an tributary of River Loire. The dam was situated after the confluence of the river with the Creuse, another major tributary. These  sub-basins historically attracted salmon, shad, sea lamprey and eels. Removal of a dam (built in 1920) in the context of a long term management plan of the river Loire, to improve the continuity and to enhance fish migration potential.

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