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The Rhone from 19 to 31 May: experiment with a new sedimentation management system

On 27 May 2016, CNR organised an institutional visit so that the region’s elected representatives could discover the new sedimentation management system of the Rhone. Every 3 or 4 years, the sediments trapped by the dams have to be flushed, in particular to prevent the risk of floods in the city of Geneva. The “mixed” system experimented this year by CNR and the Services Industriels de Genève (SIG) is based on the partial lowering of the reservoirs and on punctual dredging, intended to optimise management and reduce risks. The method implemented marks stronger cooperation between the French and Swiss stakeholders, which include the authorities and administrations involved and environmental associations and anglers.

Christian Brunier (Managing Director of Services Industriels de Genève – SIG), Luc Barthassat (Government Councillor, Department of the Environment, Transport and Agriculture of the Canton of Geneva), Elisabeth Ayrault (Chairwoman and CEO of CNR), Michel Balestra (Chairman of SIG), Jérôme Barras (Electricity Production Manager of and Director SFMCP, SIG), Christian Monteil (President of the General Council of Haute-Savoie) and Laurent Touvet (Prefect of Ain).

On the occasion of this visit, the Chairwoman of CNR, Elisabeth Ayrault, presented “Initiatives for the Future of Great Rivers” and formulated the desire that this mode of management could serve as an example for other rivers around the world. The success of this collective operation showed that it is possible to put the interests of a common resource to the fore despite the contradictions inherent to river management in general.

The Prefect of Ain, Laurent Touvet, also said he hoped that this “example would serve French-Swiss cooperation in many fields”, thus emphasising the federating capacity of the river as a shared resource.

International view of sediment management

Dams have a similar impact everywhere in the world: they impede the continuous sediment transport of rivers. The accumulation of sediments in reservoirs decreases the storage capacity of the latter and reduces the amount of sediment carried downstream (clay, silt, sand, etc.) essential for preserving aquatic fauna and flora.

River banks and seacoasts dependent on sediments are especially vulnerable, as can be seen with the narrowing or disappearance of beaches that no longer receive sand, and the acceleration of erosion of coastlines and deltas. The Mississippi delta has lost more than 4,800 km²; of the 33 largest deltas in the world, 24 are receding due to the effect of lower sediment inputs (1). Combined with the rise in sea levels, this will lead to a 50% increase of flood risks from now to 2100 and dramatic consequences for coastal populations.

(1) For further information: A full collection of good practices identified at global scale regarding sediment management: Kondolf, G. M. et al. (2014), Sustainable sediment management in reservoirs and regulated rivers: Experiences from five continents, Earth’s Future, 2, doi:10.1002/2013EF000184.

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