Vegetation management on Isère banks

Work is underway along the banks of the Isère River between Grenoble and the Domène bridge to ensure the stability of dikes and pedestrian safety. The project, set to last until October 30, is part of a long-term vegetation management plan designed to maintain flood protection structures and public safety.

Scope of the vegetation work

The Mixed Syndicate for the Hydraulic Basins of the Isère (SYMBHI) is managing the work, which runs from October 17 to October 30. It covers areas where overgrown vegetation could weaken dikes or pose a risk to people using the area. The City of Saint-Martin-d’Hères has outlined the schedule and potential impacts on local traffic.

Dual function of the dikes

The dikes along the Isère serve two main purposes: they provide walking paths for residents and protect the urban areas behind them. Their condition must be carefully monitored beyond just their visual appearance, as their structural integrity is crucial for flood prevention. SYMBHI has been responsible for their maintenance since 2021, particularly in the Jongkind quay area.

Risks from unhealthy trees

A tree that is dead, diseased, or leaning can fall onto a path or near a building. On a dike, the risk is even greater: the uprooting of a tree can remove large amounts of earth and destabilize the structure. Additionally, roots growing near walls or stone coverings can cause cracks or displacement of materials, further threatening the dikes’ stability.

Long-term effects of decomposing trees

Even after a tree is removed, its roots can leave cavities in the ground. These cavities can allow water to seep into the dikes during high water levels, carrying away soil and weakening the structure. This highlights the importance of ongoing vegetation management to prevent such degradation.

Flood protection standards

In Grenoble, SYMBHI is working to protect against a "bicentennial flood," a rare event that occurs once every 200 years. This standard is used as a benchmark for the safety of flood protection structures, which explains the careful attention given to even seemingly harmless trees.

Selective tree cutting and preservation

The project focuses on removing dead, declining, or leaning trees that could damage slopes if they fall. Healthy and notable trees are preserved where possible, and young trees with growth potential are protected. New plantings may be introduced in areas that do not compromise the safety of the dikes.

Long-term vegetation plan

The October work is part of a ten-year vegetation management plan that covers the flood protection system from Pontcharra to Grenoble. Before any cutting takes place, an ecological inventory is conducted to account for the habitats of birds, bats, and insects. Work is scheduled for autumn and winter to avoid disrupting nesting seasons.

Impact on local traffic

During the project, traffic may be temporarily interrupted on a few hundred meters in the work areas. Signage will be placed upstream and downstream to guide pedestrians and other users. Residents using the banks between Grenoble, Saint-Martin-d’Hères, and Domène should be aware of these local restrictions until the project concludes on October 30.

SYMBHI's role and future plans

SYMBHI is composed of the Isère Department and ten intercommunities, including Grenoble Alpes Métropole. Its focus is on flood prevention and river maintenance in the southern part of the department. The vegetation management program will continue beyond the October campaign, addressing other sections of the embankment system between Pontcharra and Grenoble.