Switzerland

• Lac des Dix


  • Created behind a dam
  • Four pumping stations send water through 100 km of tunnels into the reservoir
  • Aims to optimise water level for maximum availability before heavy demand periods
  • Able to maximise profits by offsetting pumping costs in summer against energy generation in winter
• Grande Dixence Dam

  • Highest gravity dam in the world
  • Initially constructed in 1960s to provide Switzerland with hydroelectric power
  • Undergone numerous additions and alterations, most recently in 2010
  • Construction was a lengthy process due to inaccessibility of site and severe working conditions
• Grande Dixence Dam

  • 285 metres high
  • Stores over 400 million m³ of water annually
  • 200 metres wide at base, 15 metres wide at top
  • Deep grout curtain surrounds dam to make foundation soil watertight
  • Aggregates obtained locally from moraine deposits
  • Catchment area of over 350 km², half from 35 glaciers
• Grande Dixence Hydroelectric Scheme

  • Drives turbines in four power stations
  • Combined capacity of 2000 GWh annually, enough to power 400,000 Swiss households
  • Stores glacial meltwater in summer, generates electricity in high demand winter period
  • One-third of Swiss electricity comes from storage power stations, another quarter from run-of-the-river schemes
• Less than 5 per cent of Swiss electricity production comes from fossil fuels, with nuclear providing the rest
• Water stored behind Grande Dixence Dam

  85% used for electricity generation, 15% used to deal with sedimentation problems
• Sediment concentrations are >300 mg/l above the dam, 20-50 mg just below the dam, and 20 mg/l 3 km downstream of the dam
• Dealing with sedimentation

  1. Some water from reservoir used to purge sediment, flushing it out and moving it downstream

  2. During these times, water has high levels of turbidity and sediment concentrations up to 20,000 mg/l
• Trapping of sediment behind the dam

  • Leads to very clear water being returned into the natural river channels below the power stations
  • This has excess energy and is being used to transport sediment, resulting in increased channel erosion
• Lack of discharge in rivers below the dam

  • Some rivers virtually dry up in summer
  • Significant contraction in the size of the channels, with the scale of contraction increasing downstream
• The amount of sediment flowing to Lake Geneva has halved since the construction of the dam
• In the Valdrôme, there is a risk of sudden and unexpected flooding when excess stored water has to be released
• The scheme has hindered both tourism and development along the valley, although local residents receive significant revenues and are strongly in favour of the scheme