human activity causing change - Grande Dixence, Switzerland

• where is the dam located?

  Southwest Switzerland
• key points about the dam

  285m high

  200m wide

  stores around 400million m^3
• key points about energy

  drives the turbine in 4 power stations with a combined capacity of 200GWh annually

  can power 400000 households

  1/3 of Swiss electricity
• what is the environmental impact of the Grande Dixence?

  - reduced flow in the Borgne River, a tributary of the Rhone, below the dam has resulted in higher concentrations of pollutants at Les Haudere from agricultural (pesticides) and domestic sources
• what is the impact on the glacial system?

  - sedimentation issues

  - when water is stored behind the dam the lack of flow means a loss of energy. as a result, sediments that were previously carried in the water settle out and deposit at rates of 20-40cm per yr

  - sediment conc are > 300mg/l above the dam

  - to solve this water is being released to flush the sediment out, high levels of turbidity and high sediment levels
• what is the impact on river channels?

  - trapping of sediment behind the dam leads to very clear water being returned into the natural river channel

  - excess energy which results in increased channel erosion

  - lack of discharge in the below dam river means some virtually dry up in the summer

  - risk of sudden and unexpected flooding when excess stored water has to be released