Human interaction with rivers

How humans interact

• They can interact in three ways:
• 1) Hydroelectric dams
• 2) Canalisation
• 3) Flood control measures

Impact of hydroelectric dams

• - Hydroelectric dams are built across rivers to control the flow of water
• - Water is stored behind the dam in a reservoir
• - The water at the base of the dam builds up and the force of gravity forces it through a pipe aka penstock located in the dam
• - the force of the moving water turns a turbine which is connected to a shaft which leads to a generator
• - this generator produces hydroelectric power which supplies power lines with electricity
• Advantages
• - generates electricity at HEP stations
• - water supply for domestic/agricultural/indusrial needs
• - ability to control the impact of flood waters
• - the reservoir can be used for recreation and aquaculture
• Disadvantages
• - relocation of people
• - removal/loss of archeological artefacts
• - A build up of sediment occurs behind the dam resulting in no alluvial deposits downstream which makes farmers turn to artificial fertilisers which is expensive and polluting

Three Gorges Dam, China (CS)

• - The largest hydroelectric dam in the world
• - located on the Yangtze River
• Advantages
• - generates electricity
• - reduces pollution as coal is used less
• - controls the flow of water which reduces the risk of flooding and erosion of the surrounding ecosystem
• - attracts a large number of tourists every year
• Disadvantages
• - the relocation of 1.3million people
• - the flooding of archeological sites
• - Increased risk of landslides

Impact of canalisation

• - canals are human made waterways as not all rivers are suitable for large boats
• - canals have been built all over the world to enable efficient water transport and are also built for irrigation purposes
• The Aral Sea in the former Soviet Union is an example of an area affected by the re-routing of rivers
• Aral Sea (CS)
• - was once ne of the four largest lakes in the world
• - two of the rivers which supplied water to it were re-routed for irrigation purposes in 1960 causing it to shrink, in 2007 it was 10% of its original size
• Effects
• - boats are now sitting on dry sea-beds
• - unemployment among fishermen as increasing levels of slat killed the fish
• - summers are dryer and hotter and winters are longer and cooler
• - land is no longer fertile

Flood control measures

• - Levees are made up of deposited material on either side of he river channel in its old age and they act as natural barriers against flooding
• - Artificial levees are also built in order to protect against flooding and to limit the flow of a river
• - as a result the river flows faster and down a narrower path with all deposition occurring on the river bed
• - A river can sometimes apply to much pressure on a levee causing it to fail and when this happened the lower reaches of the river will flood out onto the floodplain
• - Floods can damage property and even cause loss of life
• - levees are built of strong materials such as stone walls and in times of emergency sand bags

Mississippi levees (CS)

• - other examples of artificial levees can be found on the River Rhine i Germany and the River Po in Italy
• - It was constructed to hold the river within its boundaries
• - however human levees are sometimes unable to withstand the force of the river
• - This happened in 2005 when hurricane Katerina hit New Orleans and levees failed in over 50 different areas
• - 80% of New Orleans was flooded with over 4m of water
• - they failed due to water flowing over the top and under its foundations
• - 1464 people died as a result of this

The River Rhine (CS)

• - longest and most important river in europe
• - source is in the Swiss Alps and flows through Switzerland, Liechtenstein, Austria, Germany, France and the Netherlands before it enters the North Sea
• - One of the main arteries of Western europe
• - changes were made to its course, a canal network was developed
• - Dykes were constructed to prevent flooding