Dredging impact sheet

As concessionary of the Rhone, we monitor and maintain the riverbed. We carry out dredging and cleaning operations to ensure the water flows freely. Fifty operations are carried out every year, after approval is given by the administrative authorities. The impact sheets of these dredging operations can be consulted on line

The Rhone transports sediments that move randomly as a function of hydrological events, which can lead to the local accumulation of deposits. We monitor the evolution of the riverbed and carry out dredging operations when necessary.

These operations fall within a strict regulatory and environmentally friendly framework. Their characteristics and the techniques used vary according to the reaches and contexts. They concern alluvial deposits as well as vegetation debris and ice-jams in order to ensure the river flows freely. The operations are performed during the most favourable periods to reduce impacts on the reproduction and migration of animal species.

Transparency and compliance with the regulations

Sediment dredging operations are subject to the provisions of the Law on Water and Wetlands (LEMA) and to authorisations that depend on the procedures set out in the Environment Code (articles L 214-1 to 214-6) in the framework of a regular maintenance management plan.

Impact sheets

A month before any operation affecting more than 5,000 m3, CNR sends a dredging impact sheet to the relevant services and publishes it on its website. It specifies measures intended to limit the impacts. Regarding the natural transit of the Rhone (several million tons a year), dredging of less than 5,000 m3 has almost no socioeconomic or environmental impact.

Dredging or cleaning?

The use of one term or the other depends on the machines used. The term “dredging” is more often used when river equipment is employed (suction dredger, bucket dredger, etc.), while the term “cleaning”  is used when earthmoving equipment is employed (e.g., hydraulic excavators). But the use of one term for the other is not uncommon. The regulations and the principles of CNR’s operations make no distinction between them.

Ecological continuity

The Law on Water and Wetlands (LEMA) brought in the concept of ecological continuity, implying that “natural sediment transport occurs efficiently” (art. R 214-109). The ruling of 30 May 2008 requires that the material moved during dredging or cleaning is returned to the river to preserve natural sediment transport and the equilibrium of the bed. Exceptions are provided for in the case of contaminated sediments, due to their effect on aquatic habitats downstream or to technical and economic conditions.

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