Helping the Rhône Syndicat Mixte Interrégional (interregional mixed association) implement the "Plan Rhône"

In 2003, a major flooding caused by the Rhone flood affected more than 12,000 people and caused over €700 million in damage. Consequently, the public authorities launched the large-scale “Plan Rhône” to fight against flooding. Four years later, the flood management plan for downstream Rhone was implemented, with the aim of building resilience to flood risks. SYMADREM, the interregional mixed association for management of the Rhône delta and sea embankments, planned for these goals to be implemented via a programme to secure protection from Vallabrègues dam to the sea.
The mission

Protecting residents and their region

The flood in December 2003 caused four breaches in the Rhone delta protection structures, resulting in 217 million m3 of overflow. The extent of the flooding revealed the need for a coherent and compatible flood prevention policy across the entire Rhone basin.

Working alongside SYMADREM, the interregional association we have supported for the last ten years, we are applying long-term solutions to prevent the Rhône's flood risks.
Under the “Plan Rhône”, dikes were secured between Beaucaire and Fourques, and between Tarascon and Arles, cities located on the River Rhône, in Provence-Alpes-Côte d'Azur region, South of France totalling 23 linear kilometres of dikes, including a new 10-km overflow-resistant section for floods surpassing the Rhône's 100-year flood.

For this project, SUEZ Consulting was commissioned to carry out:
  • Oversee the stretch of dikes needing to be secured*, between Beaucaire and Fourques
  • Design the stretch of dikes needing to be secured between Tarascon and Arles Oversee support measures for Rhône drainage water, in the event of flooding of the Trébon plains, including development of a transfer ditch and siphon for the plains' canals*

* from design phase to delivery
Our solution

Improved flood management along the River Rhone

Securing the dike

SYMADREM's programme to secure protection addresses a number of issues:
  • Managing new urban development by reconciling risk and regional development
  • Reducing exposure to existing issues in areas liable to flooding, e.g. housing, businesses, farms, public buildings and networks
  • Securing flood protection structures in order to avoid breaches and to reduce the amount of time that land is flooded
To meet these challenges with an alternative to raising the height of existing dikes, a project which began in 2013, it was vital to allow for flooding of land upstream of vulnerable areas for infrequent floods, by developing overflow-resistant sections. It was also necessary to secure existing dikes and develop new ones to mitigate exceptional floods.

This solution has been implemented on both banks of the Rhône:

Inaugurated on November 10, 2021, the Opération Tarascon-Arles aimed to protect Arles and its surrounding area:
  • Development of a 10-km embankment on the left bank of the Rhône
  • Creation of 5-km overflow-resistant sections along the railway line
  • Extraction of 600,000 m³ of sediment downstream of Tarascon
  • Creation of a river branch located at a distance from the main bed along the Rhône, over approximately 3 km
  • Rehabilitation of a landfill using material from the construction site

Inaugurated on July 4, 2019, our teams have secured the dike between Beaucaire and Fourques to preserve the countryside in the Gard department:
  • Reconstruction and reinforcement of 13 km of dike, 5 km of which was made to be overflow resistant, representing more than 1 million m³ of materials
  • Creation of a water intake 10 m below the dike to supply an irrigation canal
  • Extraction of more than 300,000 m³ of sediment from the Rhône
  • Implementation of an innovative fibre-optic system spanning 12 km, enabling detection of unusual water inflow in the body of the dike, in order to facilitate interventions and maintenance

Implementing support measures

To support the creation of the Tarascon-Arles dike, design studies were carried out to:
  • Identify obstacles to water drainage from the River Rhône and thus improve drainage
  • Protect Tarascon's southern districts for the benchmark flood (May 1856)
  • Halve the time taken for water to drain into the Trébon plains in the event of the River Rhône flooding its banks
  • Lower the water line in the Trébon plains

To meet these challenges, SUEZ managed, from the design to the project delivery, a number of solutions implemented in 2020 and 2021:
  • Creation of a 300m-long siphon on the Alpines irrigation canal and levelling of its dike to enable drainage of the Rhône's flood overflow
  • Creation of a transfer ditch to guide water from West to East
  • Creation of a 2.2 m x 2.5 m siphon to enable Rhone water to flow under the Vigueirat canal

Next steps

Supporting measures for the Tarascon-Arles dike continue:

Securing dikes on the canals crossing Arles, in the event of the Rhone flooding its banks, to prevent districts of Arles being flooded:
  • Securing the Vigueirat's dikes where it crosses Fourchon
  • Raising the banks in the common section in Fourchon

SUEZ Consulting also supports SYMADREM as project manager on other works, currently in their design phase.

Work is due to start in Autumn 2022.
Pictures: © SYMADREM

Ameline BLIVET

Project engineer • Provence-Alpes-Côte d'Azur Region Department [email protected]