Feedback and guidelines for geomembrane lining systems of mountain reservoirs in France

Mountain reservoirs are hydraulic structures in mountains, used in ski resorts to store water, generally for producing artificial snow; there are about 120 of them in France. Despite their modest volumes (5000–400,000 m3) and dam heights of between 5 and 20 m, these structures do induce potentially high risks, due to their location in mountain at altitudes of between 1200 and 3000 m. These reservoirs are very often made watertight artificially by geomembrane. A survey conducted on about 70 of these reservoirs provided considerable information on their pathologies, incidents and even accidents and served as a basis for writing a set of guidelines for studying, designing, constructing, monitoring and rehabilitating. The paper is divided into two parts; the first based on an analysis of the 32 best documented structures is a feedback of water-tightness quality of Geosynthetic Liner Systems (GLS) at high altitudes; the second based on the guidelines above-mentioned, concerns the construction choices and behaviour of GLS at high altitudes. In particular, the guide advises using a cover layer in most cases to protect the geomembrane, and paying particular attention to the support layers and to drainage under the geomembrane.