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Hydraulic Works & Waterproofing | RUBBERFLOW® Range | 100 per cent French-made
BORFLEX seals at the heart of an exceptional hydraulic engineering project
As part of the work to restore the watertight seals on the VS4 mid-level sluice gate at the Villerest dam – a strategic structure for flood protection on the Loire – Hydrokarst, the contractor awarded the contract by the Établissement public Loire, has turned to the BORFLEX Group’s sealing solutions. This choice demonstrates the confidence placed in French expertise in the field of technical seals for hydraulic structures.
Watch a video showing the different stages of the construction project:
▶ Watch the official animation of the construction site — Villerest Dam (YouTube)
▶ Watch the accompanying video report (YouTube)
A strategic project for the Loire basin
Commissioned in 1983, the Villerest Dam (in the commune of Commelle-Vernay, Loire) is one of two key infrastructure projects managed by the Établissement public Loire, a joint authority comprising more than sixty local authorities representing 20 per cent of mainland France and 9 million inhabitants.
A 59-metre-high, 469-metre-long concrete arch dam, it serves a threefold purpose:
- Protecting communities from flooding
- Maintaining the flow of the Loire during low-water periods
- Contribution to hydroelectric power generation (provided by EDF)
💧 Hydraulics glossary: two key concepts
LOW WATER LEVEL
A period of low water, usually in summer, when the river’s flow reaches its lowest level. During the low-water period, the Villerest dam gradually releases the water stored in its reservoir to maintain the flow of the River Loire. Without this measure, the supply of drinking water, agricultural irrigation and the survival of ecosystems would be threatened over a stretch of hundreds of kilometres.
FLOOD CONTROL
A technique involving the temporary retention of a large volume of water in the reservoir during periods of heavy rainfall, in order to reduce peak flood levels downstream. A practical example: during the floods of November 2008, the Villerest dam lowered the water level at Roanne by 1.88 metres, preventing major flooding. Since it came into service, the dam has mitigated the effects of nine major floods.
Major leaks, a planned emergency operation
Significant leaks have been detected on the VS4 mid-level gate, one of the structure’s five mid-level gates. In response to this safety issue, the Loire Public Authority has 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 client has awarded the contract for the works to Hydrokarst (Jarnias Group), a company specialising in works in hard-to-reach areas, under the joint project management of BRL and EMI Ingénierie.
An extraordinary engineering process: the floating cofferdam
The complexity of the project lies in draining the valve whilst it is submerged. The solution adopted involves the installation of a coffer dam comprising eight metal caissons, each 20 metres long and weighing 35 tonnes. These 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 whilst afloat and then submerged directly in line with the sluice gate.
This technique, carried out between January and the end of February 2026, made it possible to completely isolate the VS4 valve and to access the sealing equipment under optimal safety conditions, without interrupting the dam’s flood management and low-water support operations.
▶ Watch the Hydrokarst report on the Villerest construction site (YouTube)
BORFLEX & Hydrokarst: Collaborative engineering and bespoke solutions for construction sites
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 consultancy, it quickly developed into a genuine co-design partnership between the two engineering firms to meet the specific requirements of the VS4 valve.
“The Hydrokarst teams drew on BORFLEX’s expertise to manufacture the seals required for the refurbishment of the coffer dams at the Villerest dam. The quality of the workmanship, the precision of the tolerances and the adaptation to the specific constraints of the structure 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.
BORFLEX’s responsiveness and technical support also helped ensure that the on-site operations remained on schedule.”
Amaury MOURIER DES GAYETS, Hydromechanical Project Manager, SDEM, HYDROKARST, Jarnias Group
An industry first: corner blocks
One of the major challenges lay in the geometry and manufacture of the valve’s angle blocks. By combining their expertise, the design teams at Hydrokarst and BORFLEX opted for a disruptive approach: manufacturing the angle blocks from rubber
- Technical advantage: Millimetre-level precision, perfectly suited to the project’s stringent tolerances.
- Economic benefit: This method resulted in a net profit of €20,000 from the transaction.
The challenge of the very senior year with RUBBERFLOW® D650
For the body of the seal, 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 from RUBBERFLOW® D650, a state-of-the-art elastomer formulation specifically developed to withstand abrasion and high pressures, and to ensure extremely low compression set, thereby guaranteeing a perfect, long-term seal in submerged environments.
French expertise in hydraulic sealing
With over 65 years’ experience in rubber processing, the BORFLEX Group has established itself as a leading player in France and across Europe in the design, formulation and manufacture of bespoke elastomer and composite components. Its strength lies in the complete vertical integration of the production chain: from formulation laboratories right through to production and on-site installation.
The French Group has 11 production sites in France, employing more than 375 staff, as well as two dedicated laboratories and five design 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® range: a bespoke solution for hydraulic structures
For waterproofing applications on hydraulic structures — dams, upstream and bottom gates, cofferdams — BORFLEX has developed the RUBBERFLOW® range, a line of elastomers specially designed to meet the demands of river environments. Beyond simply providing a watertight seal, these materials ensure:
- Abrasion and tear resistance
- Resistant to fluctuations in pressure and temperature
- Chemical compatibility with natural waters
- Long service life in submerged environments
- Limited permanent deformation after compression
RUBBERFLOW® compounds meet the specifications of the leading French clients in the hydraulics 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 gateboats
- Valves, sluices, pumping stations
- Quay fenders
The project in figures
| Client | Loire Public Institution |
| Project owner | Hydrokarst (Jarnias Group) |
| Project management | BRL & EMI Engineering |
| Supplier of seals | BORFLEX Group: RUBBERFLOW® range |
| 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 tonnes |
| Dam | 59 m high – 469 m long – Reservoir capacity of 132.6 Mm³ |
| Flood peaks since 1985 | 9 major floods, including a drop of 19 cm in Roanne in 2008 |
Timetable for the main stages of the works
Actors’ comments
“Securing the Villerest dam means fully assuming our responsibility towards the local areas. The waterproofing works now underway are designed to ensure the long-term viability of this strategic structure and to maintain its key functions: protecting against flooding and supporting the Loire during periods of low water.
Taking action now means choosing to be proactive, prioritising safety and acting in the public interest.”
Daniel Fréchet, Chair of the Loire
Public Authority and Vice-Chair of the Loire Department.
“The Villerest dam is a strategic structure for the entire Loire basin. It provides protection against flooding but is also vital to meeting the needs of all users, particularly for irrigation, which is essential to regional agricultural activity – and extends beyond administrative boundaries.
The commitment of the Auvergne-Rhône-Alpes region, alongside the Loire Public Authority, is crucial: managing and maintaining infrastructure on this scale is a major political challenge. For the benefit of the local areas and in the interests of all stakeholders in the basin.”
Raymond Vial, Vice-President of the Établissement public Loire in charge of dams, Regional Councillor for Auvergne-Rhône-Alpes
Multimedia resources
To provide a deeper understanding of this exceptional project, the Loire Public Authority has made the following resources available:
▶ 🎥 Official animation — Stages of construction of the Villerest
dam ▶ 🎥 Video report on the ongoing construction work (2026)
▶ 🌐 360° virtual tour of the Villerest
dam ▶ 🌐 BORFLEX Group’s official website
BORFLEX: 100 per cent French industrial roots
In a sector where the traceability of materials and the reliability of products are non-negotiable requirements, BORFLEX relies on a production process carried out entirely in France. Formulations are developed and monitored in-house, in accordance with the technical specifications of the project owners. The Group operates throughout France and exports its solutions to more than 30 countries.
Press contacts
Press enquiries — BORFLEX
Group Website: www.borflex-group.com
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Press enquiries — JARNIAS
Group Claire du BOISLOUVEAU: Marketing and Communications
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+33 6 69 13 33 61
Press
enquiries: Loire Public Institution
Sylvie Asselin, Communications Officer: 02 46 47 03 09 — Enable JavaScript to view this email
Maxime Tourné, Dam Manager: 06 30 38 59 44 — Enable JavaScript to view this email