• Client: SATA
• Consulting engineer: Alpes Ingé
• Earthworks Contractor: Socco
• Waterproofing Group: N.M.G. Étanchéité - main contractor and Polen’
• Serge Ferrari composite material: Précontraint 1215 geomembrane
The Serge Ferrari Group invites you to an outstanding construction project at an altitude of 3000 metres: installation of 32,500 m² of Précontraint 1215 composite membrane at the heart of the Herpie high-altitude storage reservoir, the highest in Europe! This gigantic artificial lake with a capacity of 165,000 m3 will be used to supply water for artificial snow production and coverage of the famous Sarenne ski run (Europe’s longest) in the Alpe d’Huez skiing area.
An outstanding construction project
“The Sarenne ski run – with its exceptional length and gradient – is unique but is a victim of its own success! As records over the last 15 years or so show, snow falls have been reducing and making the situation a little critical in terms of the snow cover expected by lovers of nature and real thrills” declares Christian Reverbel, SATA’s (Société d’Aménagement Touristique de l’Alpe d’Huez et des Grandes Rousses) ski run manager for Alpe d’Huez.
The idea of the Herpie high-altitude storage reservoir goes back a decade! This was therefore a well thought out, long-term process involving conservation of the entire ski run length and gradient, while maintaining the full unity of this project comprising 3 distinct yet complementary components:
- The artificial lake
- A technical building
- A pipe network installed over the entire length of the ski run.
“We will spray water for 10 hours every night, based on the knowledge that a snow canon consumes 40 to 50 m3 of water/hour, and we will have 72 snow canons positioned to cover 70% of the ski run area. We therefore borrow this water and crystallise it during a winter to give pleasure to skiing and snowboarding lovers, before returning it to the natural system from which it came by either melting or evaporation at the end of each spring” explains the Alpe d’Huez ski run manager.
“This lake integrates perfectly into the surrounding environment. It is the outcome of 11 years of studies, during which we performed specific inventories of not only the flora and fauna, but also the fish stocks in the lower part of the ski run. The ski run was developed in partnership with ecologists and full re-vegetation will be performed throughout the development coverage. Our aim is to meet artificial snow production requirements in an environmentally reasonable and reasoned manner” concludes Christian Reverbel.
Why was Précontraint 1215 selected?
The strength of this 100% recyclable Serge Ferrari geomembrane guarantees the installation’s absolute watertightness. Its breaking strength is 550 daN/5cm compared with conventional geomembranes only offer approximately 100 daN. Its capacity for absorbing high-altitude temperature variations and constraints, such as avalanches, stone falls, etc., is optimal.
The specific nature of its formulation ensures high tolerance under extreme temperatures and temperature variations, which can range from -50 °C to +50 °C.
Other advantages: Its dimensional stability, flexibility and resistance to UV radiation (comparable with Saharan levels at 2,500 – 3,000 metres).
Geomembrane transport and installation
61 rolls (200 lm each) of Précontraint 1215 composite membrane were deposited on site by helicopter.
Roll width assembly by hot air welding was performed on site by contracting group N.M.G. Etanchéité and Polen’. “This project is very unusual in terms of its size since storage reservoir capacity is conventionally 70 – 100,000 m3. In this case, the 165,000 m3 obviously create greater constraints – in particular structural – even though we are in favourable geological conditions. We have rock in virtually the entire site area, which guarantees natural ground stability” explains Franck Machet, Alpes Ingé’s geotechnical and environmental design manager.
“This project therefore doesn’t raise any specific problems, but rock blasting always represents a delicate stage”. Concerning Herpie, this operation enabled us to build the downstream embankment, to produce the materials used for reservoir bottom drainage and the fine materials used to cover its internal slopes prior to laying the Serge Ferrari geomembrane” explained Franck Machet.
- A drainage geocomposite specifically designed and laid beneath the Précontraint geomembrane to ensure its protection allows all minor water infiltrations from the reservoir slopes to be collected
- The 1.25 mm thick Précontraint 1215 geomembrane ensures watertightness
- A soil retaining geocomposite guarantees stability of confinement material (30 cm of stone) protecting the Serge Ferrari geomembrane.
The reservoir water intake is located on the Sarenne mountain stream. Water is only extracted when the glacier snow, which supplies the mountain stream, is melting between May and July.