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Reservoir lowering operations in 2016: CNR's actions

The first operations to partially lower the reservoir of Verbois in Switzerland will take place from 19 to 31 may 2016. CNR assists them with its 6 hydropower installations from Génissiat to Sault Brenaz to limit their impact on the Rhone.

The reservoir lowering operations from 19 to 31 May 2016

carte_amenagement_typeThe Service Industriels de Génève (SIG) expressed the need to partially lower the reservoir of Verbois in 2016, unless hindered by bad weather which may postpone the operations by no more than 7 days. The SIG plans to remove 1.9 million tons of material. In comparison, in 2012, 2.6 million tons of sediment were removed.

Who decides to implement these operations?

At the request of the French authorities, CNR presented a general operating procedure for its installations to assist the lowering and, in a more general way, the new ten year sediment management plan. It completed an environmental impact study which contains a number of measures for preserving natural habitats and a file on protected species.

Following a public enquiry held in autumn 2015 in the municipalities concerned and an examination by government services, CNR was authorised to establish its assistance  procedures by virtue of an inter-prefectural ruling issued on 16 march 2016.

A second inter-prefectural ruling was associated with it to define the implementation of measurements and specific actions to mitigate, compensate, assist and monitor protected species (birds, beavers, etc.) in the most sensitive areas.

CNR’s actions during the operations

France, Haute Savoie (74), Seyssel, barrage usine de SeysselCNR intervenes on its 6 hydropower installations on the Upper Rhone from Génissiat to Sault-Brenaz to ensure the transit of the sediments, limit the aggradation  of its reservoirs and maintain the quality of water and biodiversity.

It acts in close collaboration with the Swiss operator and under the control of the adminsitrative authorities.

  • Piloting the installations to control sediment flows

Operations are performed to lower the level of the reservoirs while limiting aggradation:
Génissiat will be lowered from 10 to 17 metres almost simultaneously with those of Verbois and Chancy-Pougny so that the sediments arriving from upstream transit via the reservoir without being deposited. CNR’s 5 other reservoirs will also be lowered from 0.4 to 1.5 m.

  • Controlling and evaluating the impacts of these operations on the environment

Monitoring is performed before, during and after the operations to assess water quality, and respect and preserve the bypassed natural sections of the Rhone rich in biodiversity. Sixty measurement sites located along the River will allow monitoring concentrations of suspended matter. Monitoring of drinking water catchment zones will also be performed.

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