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Glaciation 4b - Case study of one glaciated landscape that is being used…
Glaciation 4b - Case study of one glaciated landscape that is being used by people
Impacts
Glacial system impacts
When water is stored behind the dam, the lack of flow means a loss in energy and the deposition of sediment load behind the dam 20-40cm a year
Water is used to 'flush' the system to move sediment downstream
15% of the meltwater is used to combat sedimentation (Particles settling at the bottom of the dam)
The water has a high level of turbidity and high sediment concentrations
Environmental impacts
Have been minimised to ensure that the area remains an attractive environment for walkers, cyclists and hikers
Pumping stations and power plants are largely built underground to retain the aesthetics of the location
Reduced flow in the Borgne River has resulted in higher concentrations of pollutants at Les Haudere from both agricultural and domestic sources
River channels
Trapping of sediment behind the dam leads to very clear water being returned into the natural river channels
Sediment flowing into Lake Geneva has halved since the construction of the dam
Lack of discharge in below dam rivers mean some dry up in summer
It has excess energy as non is being used to transport sediment and results in increased channel erosion
Low valley impacts
There is a risk of sudden and unexpected flooding when excess stored water has to be released in the Val d'Herens. This has hindered both tourist use and the development along the valley floor
In December 2000 a high pressure pipeline burst, causing a landslide which wiped out a small hamlet and killed 3 people
Irrigation
Glacial sediments traditionally lined and sealed irrigation channels flowing over permeable rock
Increased dam storage and sediment deposition in reservoirs have reduced the amount of sediment in these channels
Additional measures such as channel lining are now required to prevent the loss of water through infiltration
The future
Climate change is producing higher rates of glacier melting in the Swiss Alps and the meltwater available to create hydropower is increasing
Eventually glaciers may shrink so much that
meltwater supply is likely to diminish
Altering sediment supply and transportation even further
Dam construction
Importance
Control flooding
Regulate sediment budgets
Store water for irrigation
Generate hydropower
What can it alter ?
Downstream discharge and river channel habit
The composition of texture of sediment
Nutrients fluxes and biochemical cycling
Population dynamic (Both animal and human ) Thirlmere
Grande Dixence Dam
700 m long and 285m high
Stores 400 million m3 of water a year
Concrete gravity dam
Dam was built in 1961
4 power stations attached to the dam, providing energy for 400,000 homes
85% of the meltwater is used for electricity generation
Large tourism industry based around the dam/lake and valley with guided tours and helicopter rides above the dam
Power station is mostly underground
Highest gravity dam in the world
It stores glacial meltwater during the summer and then uses it to generate electricity during the high demand period of the winter