4.b. Human activity causes change within glaciated systems (Case study)

What is the case study for a glaciated landscape being used by humans

The Grande Dixence dam in Val des Dix, Switzerland

Describe the Grande Dixence dam

Highest gravity dam in the world
Constructed from 1950 onwards
Cost 1.6 billion Swiss Francs
Fed by 35 glaciers

Explain the concept of a gravity dam

Gravity holds dam into the ground, stopping the weight from the water pushing the dam down

What does the Grande Dixence dam provide Switzerland with?

it provides Switzerland with HEP, hence why they wanted to spend so much money building it. By creating energy within the country this means Switzerland doesn't have to rely on external energy imports as much

How much water does the Grande Dixence dam store

Over 400 million m3 of water a year

Is the dam used all year round

It stores meltwater in the summer so that it can be used in the winter to generate more energy. More energy is needed in winter as people need more heating etc

How many homes does the dam fuel

400,000 Swiss homes per year

How is water transported to the Grande Dixence dam?

Through 100km of tunnels and 4 pumping stations

How many power stations are in the grande Dixence dam?

Four

What percentage of stored water is used for electricity generation?

85%

Why is a glaciated landscape suitable for the Grande Dixence dam?

Steep sided valleys, formed by glaciated, allow for the dam to store a large volume of water.

How does the dam impact the environment -> tourists

It is a big tourist spot so its aesthetics need to be maintained
This means pumping stations are built underground or well-concealed so that the environment remains attractive for walkers, cyclists and hikers

Is there any pollution because of the dam

Holding water back results in lots of pollution
We see this in the Borgne River below the dam, where there is reduced flow
In the Borgne there are high concentrations of pollutants

What is the water in the dam used for

85% is used for electricity generation
15% is used to deal with the problems of sedimentation

What is sedimentation

When we hold water back, this means the lake above is stagnant until we let it flow
Therefore a lot of sediment is held back and there isn't enough energy to push it through
Hence, 15% of the dam's water is used to flush the sediment through

Effects of trapping sediment -> clear water

The 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 as none is being used to transport sediment, resulting in increased channel erosion due to more kinetic energy

Effects of trapping sediment -> lack of discharge etc

The below-dam rivers lack discharge meaning they can dry up in the summer
The size of the channels have decreased as you go further downstream
The amount of sediment flowing into Lake Geneva has halved since the dam's construction

How will the dam's impacts on the glacial system change in the future

Because of climate change there will be higher rates of glacial meltwater
This means there is more meltwater available, creating more HEP
But the glacier will shrink because of climate change, overall meaning the meltwater supply will diminish
This will alter sediment supply even further