Caux Seine agglo & NGE are rehabilitating an ecosystem in the heart of the Seine valley

This work, which will take place during the second half of 2025, is part of a territorial strategy for the preservation of wetlands.

Designed by the engineering firm Alise Environnement, this project is being carried out by the companies NGE through its subsidiary GUINTOLI (lead contractor), Nature Environnement Terrassement (NET) and Biod.IV

Led by the Caux Seine Agglo urban community, the project aims to restore the site's ecological balance and strengthen its resilience to climate change. By restoring the wetland's natural functions, this rehabilitation will also allow the Caudebecquet site to act as a buffer during floods, thus contributing to the protection of downstream areas from flooding.

The wetland, crossed by the Rançon and its tributary the Fontenelle, is located a few hundred meters from the Seine. This area has suffered successive degradations over time: filling with inert materials from constructions on site and nearby, installation of the lagoons of the municipal wastewater treatment plant, and exploitation of the rest of the site as successive poplar plantations.

Committed to preserving natural resources and the ecological transition of the region, Caux Seine Agglo and its economic development agency, Caux Seine Développement, launched a project in June 2025 to rehabilitate the Caudebecquet wetland, located in Rives-en-Seine, in the heart of the Boucles de la Seine Normande Regional Natural Park. Adjacent to the Saint-Wandrille marsh, a Natura 2000 protected site, the wetland will undergo ecological and hydrological restoration, with the aim of restoring its natural functions and sustainably preserving its aquatic and wetland ecosystems.

An ambitious operation with multiple components

The project has been awarded to a consortium comprising GUINTOLI (lead contractor), and subcontractors NET and Biod.IV. The works, which will take place from June 15th until the end of 2025, include:

• Preparatory work: securing the site, clearing any doubts about pyrotechnics, harvesting the poplar grove, draining the lagoon basins.
• Earthworks and hydrological restoration: stripping of 32.000 m2, removal of 42.000 m3 of spoil, creation of a new riverbed and ponds.
• Environmental treatment: clearing of invasive alien species hotspots (2.000 m3), renaturalization and planting.
• Structures and pedestrian paths: footbridges on micropiles, fences, educational walk.

The construction site is subject to rigorous technical and environmental monitoring, with specific precautions related to the shallow water table, aquatic fauna, and the management of invasive species. Technical monitoring, in particular, requires precise phasing of interventions and the implementation of procedures overseen by specialized companies to guarantee the safety of the teams and regulatory compliance. The treatment of invasive plant species is governed by strict protocols to prevent their spread, including targeted excavation and the export of contaminated soil to appropriate treatment centers.

Positive impacts for ecosystems and residents

The project aims to:

• Restore the ecological and hydrological continuity of the area.
• Re-establish a natural flood expansion zone.
• Protecting aquatic and wetland ecosystems.
• Integrate an educational trail accessible to the public (section of the GR 2 crossing the site).

It is part of a comprehensive approach to the rehabilitation of a wetland, linked to the adjacent Natura 2000 site, and demonstrates the ability of the agglomeration, NGE and other participating companies to combine ecological engineering and sustainable commitment.

For Bastien CORITON, Mayor of Rives-en-Seine and Vice-President of Caux Seine agglo: “With this restoration project in the Caudebecquet wetland, we are revitalizing an exceptional natural site and strengthening the protection of our ecosystems against climate change. This project concretely illustrates our commitment, in Rives-en-Seine and within the Caux Seine agglomeration, to combine the preservation of biodiversity, the safety of residents and hikers, and the enhancement of our natural heritage.”

According to Louis DECOTIGNIE, Operational Director of NGE Normandy Centre-Val de Loire: "This ecological engineering project is a concrete example of our commitment to preserving natural resources. It mobilizes our expertise in planning, civil engineering and biodiversity to restore a wetland essential to the balance of the territory."

Key figures:

• 42.000 m3: excavated material removed from the site. Part of this material will be reused as fill on site to recreate the topographical features of the project, while the rest will be transported to approved storage facilities.
• 1.300 m3: volume dedicated to the creation of a new riverbed.
• 4.000 hygrophilous plants replanted on site.
• 2.000 m3: volume removed to eliminate invasive alien species. These materials will undergo treatment according to a specific protocol, including the export of contaminated soil to specialized treatment centers.
• Cost of works: €1.200.000 excluding VAT.