1 IGC 2003, Reykjavik Geothermal use of tunnel waters – a Swiss speciality

Switzerland accommodates a substantial part of the Alpine chain. In such mountainous terrain, railway and road tunnels as well as major galleries drain water from their surrounding rock masses. The temperature of this inflow water depends on the cover thickness; in some cases it can reach more than 50 °C. The collected water flows under gravity to the portals; provided a sufficient flow rate, various types of installations at or near the tunnel portals can thus be supplied with heat. There are over 700 road or railway tunnels in Switzerland. A potential study screened first 150 tunnels from where 15 objects were selected for more detailed studies. Their heat potential is estimated to be greater than 30 MWth. Six heating systems are already in operation near portals of the St.Gotthard, Furka, Mappo-Morettina, Hauenstein, Ricken, and Grand St.Bernard tunnels, with installed capacities between 0.2 to 2 MWt). Several further projects are at various stages of development. The heat potential at the portals of the two base tunnels under construction for the AlpTransit system (Lötschberg, 35 km long and Gotthard, 57 km) is estimated to range between 4 and 23 MWth, with a total of approximately 29 MWth. Key words: tunnel water inflow, rock and fluid temperatures, heating system