Switzerland – Grande Dixence Dam

what type of landscape is Grande Dixence dam located in

a valley glacier influenced by humans

what makes grand dixence dam unique

the worlds tallest gravity dam-285m

how much water can reservoir store (lac dis dix)

400 million m cubed

When was the dam built and at what cost?

1960s, 1.6bn swiss francs

How much electricity does the dam produce

enough to supply 400,000 homes

How is water use managed seasonally?

water pumped by in summer- low demand and cheap costs and released in winter- when in high demand and high costs

How quickly can the dam generate power?

under 4 minutes

What is its energy output comparable to?

nuclear power station

How is water supplied to the reservoir?

through tunnels and lifts from 35 glaciers

what is lac des dix

the reservoir

Why are glaciated valleys suitable for dams?

u shaped valleys create natural reservoirs and store water

How does relief help energy production?

steep slopes increase potential and kinetic energy

Why is hydroelectric power (HEP) important in Switzerland?

renewable and produces no carbon emissions

How much of Switzerland's energy comes from HEP?

over 1/3

How much of Switzerland's energy comes from fossil fuels?

less than 5%

hat advantage does the reservoir provide over wind/solar?

reliable energy generation on demand- wind and solar and dependent on the weather

Why is the area popular with tourists?

attracts hikers and nature enthusiasts

How was visual pollution reduced?

pumping stations are underground or concealed

How has the dam increased tourism?

cable cars, guided tours, hiking trails and helicopter rides

What happens to sediment in the reservoir?

builds up due to low energy and flow

What is the rate of sediment build-up?

20-40cm per year

How does sediment concentration change downstream?

******************************

Why is there less sediment downstream?

trapped in reservoir

How does reduced sediment affect river energy?

more energy available, increasing erosion

How has sediment supply to Lake Geneva changed?

is has halved since dam was built

How is sediment managed in the reservoir?

15% reservoir supply purged to flush sediment downstream

What happens during sediment purging?

water gains high energy, increasing erosion and channel scour

How was sediment historically used downstream?

to line irritation channels over permeable rock

Why is lining irrigation channels over permeable rock no longer effective?

Reduced sediment supply due to trapping in the river

what problem does high water velocity cause?

increased infiltration an water loss

how is high velocity water problem managed?

artificial water linings

What happens to river flow in summer?

restricted flow reduces discharge- some rivers dry up

What is the impact of reduced discharge on pollution?

higher concentration of pollutants in river-bornge

what is a GLOF

glacial lake outburst flood

why has GLOF increased?

meltwater unable to build up since its transferred directly to storage in reservoir

when is flood risk highest?

purging events

Which area is most affected by flood risk?

val des dix

How have people responded to flood risk?

tourists and residents buildings have been moved further form river/reservoirs

How does climate change affect glacier melt (short-term)?

increases meltwater and HEP potential

What is the long-term impact on glaciers?

half alpine glaciers are expected to disappear by 2050

How will this affect HEP in the future?

reduced water supply so low HEP generation

How will sediment supply change long-term?

further reduction in sediment entering rivers- more flood risk