Villerest Dam
BORFLEX Seals at the Heart of an Exceptional Hydraulic Project
Hydraulic Works & Waterproofing | RUBBERFLOW® Line | 100% Made in France
As part of the waterproofing renovation of the VS4 mid-level gate at the Villerest Dam—a strategic structure for flood protection along the Loire River—Hydrokarst, the contractor awarded the contract by the Établissement public Loire, turned to the BORFLEX Group for its waterproofing solutions. This choice demonstrates the confidence placed in French expertise in the field of technical seals for hydraulic structures.
Watch a video to learn about the different phases of the construction project:
| ▶ Watch the official animation of the construction project — Villerest Dam (YouTube) |
| ▶ Watch the accompanying video report (YouTube) |
SUMMARY
A Strategic Project for the Loire River Basin
Major leaks, a planned emergency response
BORFLEX & Hydrokarst: Collaborative engineering and custom solutions for the project
The Project in Numbers
Timeline of the main construction phases
Words from key players
Multimedia resources
Press Contacts
A Strategic Plan for the Loire River Basin
Commissioned in 1983, the Villerest Dam (in the municipality of Commelle-Vernay, Loire) is one of two key infrastructure projects managed by the Établissement public Loire, a joint authority that brings together more than sixty local governments representing 20 percent of mainland France and 9 million residents.
A 59-meter-high, 469-meter-long concrete arch-weight dam, it serves three purposes:
- Protecting Communities from Floods
- Maintaining the Loire River's Flow During Low-Water Periods
- Contribution to hydroelectric power generation (provided by EDF)
| 💧 Hydraulics Glossary: Two Key Concepts |
| LOW-WATER PERIOD — A period of low water levels, typically during the summer, when the river’s flow reaches its lowest point. During low-water periods, the Villerest Dam gradually releases the water stored in its reservoir to maintain the flow of the Loire River. Without this measure, the drinking water supply, agricultural irrigation, and the survival of ecosystems would be threatened over hundreds of kilometers. FLOOD PEAK REDUCTION — A technique that involves temporarily holding a large volume of water in the reservoir during heavy rainfall to reduce peak flood levels downstream. Real-world example: During the November 2008 flood, the Villerest Dam lowered the water level in Roanne by 1.88 meters, preventing major flooding. Since it began operating, the dam has mitigated nine major floods. |
Major leaks, a planned emergency response
Significant leaks were detected on the VS4 mid-level gate, one of the structure’s five mid-level gates. In response to this safety concern, the Loire Public Authority launched a major operation to fully restore the watertight integrity of this essential hydraulic component, at a total cost of 2.75 million euros.
The project owner awarded the contract for the work to Hydrokarst (Jarnias Group), a company specializing in work in hard-to-reach areas, under the joint project management of BRL and EMI Ingénierie.
An Unconventional Engineering Process: The Floating Coffer Dam
The complexity of the project lies in drying out the valve while it is submerged. The chosen solution involves installing a coffer dam consisting of eight metal caissons, each 20 meters long and weighing 35 metric tons. They were hoisted from the RD18 road bridge, requiring the simultaneous use of three very high-capacity cranes and the temporary closure of the road. The caissons were positioned by floating them into place and then submerged directly in front of the valve.
This technique, implemented between January and the end of February 2026, made it possible to completely isolate valve VS4 and gain access to the sealing components under optimal safety conditions, without interrupting the dam’s flood control and low-water support operations.
BORFLEX & Hydrokarst: Collaborative Engineering and Custom Solutions for Construction Projects
The success of such an operation depends largely on the reliability and surgical precision of the sealing components used. Although the relationship between Hydrokarst and BORFLEX began as a standard consultation, it quickly evolved into a true co-design partnership between the two engineering firms to address the specific requirements of the VS4 valve.
“The Hydrokarst teams relied on BORFLEX’s expertise to manufacture the seals needed to rehabilitate the coffer dams at the Villerest Dam. The quality of the workmanship, the precision of the tolerances, and the adaptation to the structure’s specific constraints were decisive factors. This equipment enabled us to seal the VS4 gate’s sluice under demanding conditions, ensuring a reliable and long-lasting watertight seal.
Amaury MOURIER DES GAYETS, Hydromechanical Project Manager, SDEM, HYDROKARST, Jarnias Group
BORFLEX’s responsiveness and technical support also helped ensure that the on-site operations remained on schedule.”
An industry first: corner blocks
One of the major challenges lay in the geometry and fabrication of the valve’s corner blocks. By combining their expertise, the engineering departments at Hydrokarst and BORFLEX opted for a disruptive approach: manufacturing the corner blocks out of rubber.
· Technical advantage: Millimeter-level precision that is perfectly suited to the project’s strict tolerances.
· Economic benefit: This method resulted in a net gain of €20,000 on the transaction.
The Challenge of the Very Large Section in RUBBERFLOW® D650
For the seal body, BORFLEX faced a major challenge: designing and extruding a seal with a very large cross-section. Developing the extrusion die required a high level of technical expertise from the production teams. The seal was manufactured using RUBBERFLOW® D650, a state-of-the-art elastomer formulation specifically developed to withstand abrasion and high pressures and to ensure extremely limited permanent deformation after compression, thereby guaranteeing a perfect, long-term seal in submerged environments.
French Expertise in Hydraulic Sealing
With more than 65 years of experience in rubber processing, the BORFLEX Group has established itself as a leading player in France and Europe in the design, formulation, and manufacture of custom elastomer and composite parts. Its strength lies in the complete vertical integration of the industrial chain: from formulation laboratories through production to on-site installation.
The French Group has 11 production sites in France, employing more than 375 people, as well as two dedicated laboratories and five engineering offices. This structure ensures complete control over blends and formulations, which directly determines the durability and performance of the products in harsh environments.
The RUBBERFLOW® line: a tailored solution for hydraulic structures
For sealing applications in hydraulic structures—dams, upstream and bottom gates, and cofferdams—BORFLEX has developed the RUBBERFLOW® line, a range of elastomers specifically designed to meet the demands of river environments. Beyond their basic sealing function, these materials provide:
- Abrasion and Tear Resistance
- Resistant to pressure and temperature fluctuations
- Chemical Compatibility with Natural Waters
- Long service life in submerged environments
- Limited compression set
RUBBERFLOW® compounds meet the specifications of the leading French contractors in the hydraulic sector (EDF, VNF, CNR) and cover all types of seals for hydraulic structures:
- Seals for surface valves, bottom valves, and mid-depth valves
- Cofferdams and lock gates
- Valves, locks, pumping stations
- Dock fenders
The Construction Project in Numbers
| Project Owner | Loire Public Institution |
| Project Manager | Hydrokarst (Jarnias Group) |
| Project Management | BRL & EMI Engineering |
| Seal Supplier | BORFLEX Group: RUBBERFLOW® product line |
| Total amount | 2.75 million euros |
| Total duration | June 2025 – Second half of 2026 |
| Cofferdam | 8 metal containers, each 20 m long and weighing 35 metric tons |
| Dam | 59 m high – 469 m long – Reservoir capacity of 132.6 Mm³ |
| Floods Have Been Mitigated Since 1985 | 9 major floods, including one with a rise of −19 cm in Roanne in 2008 |
Schedule of Key Construction Phases
Quotes from Actors
“Securing the Villerest Dam means fully assuming our responsibility toward these regions. The waterproofing work underway today aims to ensure the long-term viability of this strategic structure and to maintain its primary functions: protecting against flooding and supporting the Loire River during low-water periods.
Daniel Fréchet, President of the Loire Public Institution
Taking action now means choosing to be proactive, to prioritize safety, and to serve the public interest.”
Vice President of the Loire Department.
“The Villerest Dam is a strategic structure for the entire Loire River basin. It provides protection against flooding but also determines the ability to meet all water needs, particularly irrigation, which is essential to regional agricultural activity—and extends beyond administrative boundaries.
Raymond Vial, Vice President of the Loire Public Agency in charge of dams, Regional Councilor for Auvergne-Rhône-Alpes
The commitment of the Auvergne-Rhône-Alpes region alongside the Loire public agency is crucial: managing and maintaining infrastructure of this scale is a major political issue—for the benefit of the local communities and in the interest of all stakeholders in the basin.”
Multimedia Resources
To help you better understand this exceptional project, the Loire Public Agency provides the following resources:
BORFLEX: 100% French industrial roots
In an industry where material traceability and product reliability are non-negotiable requirements, BORFLEX relies on production carried out entirely in France. Formulations are developed and tested in-house, in accordance with the technical specifications provided by clients. The Group operates throughout France and exports its solutions to more than 30 countries.
Press Contacts
| Press Contact — BORFLEX Group Website: www.borflex-group.com Email: e.roegiers@borflex-group.com | Press Contact — JARNIAS Group Claire du BOISLOUVEAU: Director of Marketing and Communications cduboislouveau@groupejarnias.fr +33 6 69 13 33 61 |
Press Contact — Loire Public Institution
Sylvie Asselin, Communications Officer: 02 46 47 03 09 — sylvie.asselin@eptb-loire.fr
Maxime Tourné, Director of Dams: 06 30 38 59 44 — maxime.tourne@eptb-loire.fr
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