Grand Dixence Dam: Human activity - glaciated landscape

• What human activity is taking place and why?

  • Grand Dixence Dam was built in the 1960s at a cost of 1.6 billion Swiss Francs and is 285 m tall
  • The purpose of the Grand Dixence project was to provide Switzerland with hydroelectric power
  • It can hold up to 400 million m^3 of water and generates power for 400,000 homes
  • With a catchment of 35 glaciers, it is currently the largest dam in Europe
  • The dam stores glacial meltwater in summer, and then releases it through turbines to generate electricity in winter when demand is high
• How does this human activity impact processes and flows

  It impacts the glacial system

  • Lack of water flow means sediment is deposited behind the dam
  • Sediment concentrations are high above the dam ( 300 mg/l ) but there is less sediment downstream ( 20 mg/l )
  • Sediment flowing into the Lake Geneva has halved since construction of the dam
  • Periodically ( 1-2 times a year ) , water is released to flush out the accumulated sediment, moving it downstream > high turbidity of 20,000 mg/l > temporary flooding in Val de Herens
• How has this activity changed the landform?

  Local/regional impact on the river channels downstream of the dam

  • Trapped sediment behind the dam > very clear water downstream > excess energy as none is used to transport sediment > increased channel erosion
  • Lack of discharge in below dam rivers > some dry-up in summer
  • Lack of below dam flow > higher concentrations of pollutants at Les Haudere from both agricultural and domestic sources
  • In Val De'herens > risk of sudden unexpected flooding when excess store water is released
• Consequences for the landscape

  • Significant contraction in the size of the river channels
  • The scale of contraction increases with distance downstream from the dam