River Flooding: River Chang Jiang

• The Yangtze basin covers an area of approximately 2 million square kilometers (780,000 sq mi), with a population of around 450 million people.
• Background:

  • China is largest country in the world in terms of population, land mass and economically.
  • China is plagued by earthquakes, typhoons and flooding events.
  • Yangtze river in 6380km long.
  • Third longest in the world.
  • River can rise to extremely high levels.
  • Caused by monsoon rains and snowmelt from the Himalayas.
• River floods:

  • It floods annually, sometimes its floods are catastrophic.
  • 1931, 1934, 1954, 1998.
  • During 20th century, 300,000 killed by the floods.
  • 1998 event was blamed on El Nino.
• Human causes:

  • Urban population boom.
  • Many cities are situated along the river banks.
  • Impermeable surfaces encourage surface runoff.
  • Factories have been built in rural areas on floodplains.
  • Done to counter rural - urban migration.
  • Deforestation means less interception (1960s).
  • Mismanagement of deforested land.
  • Led to an increase in soil erosion and more silt in river channel.
  • Canalisation of river to improve transport has straightened the river - reduces lag time.
  • Flood protection embankments have limited the expansion of the river.
  • Global warming leads to higher rainfall.
• Impacts of 1998 flood:

  • 1 in 100 year event.
  • 45 metres high at its peak.
  • 240mn people in seven provinces were affected.
  • 4000 drowned.
  • Countless farm animals were killed.
  • Huge areas of crops destroyed.
  • 14mn were homeless for months as their houses were repaired.
  • Unemployment was high as factories were repaired.
  • Total economic cost is unknown, but thought to extraordinary.
• Management Scheme: Three Gorges Dam

  • Located downstream of Chongqing.
  • 660km long, 1km wide.
  • Construction began in 1994 and ended in 2006.
  • Reservoir fully filled in 2009.
  • Dam is 2.3km long and 200 metres high.
  • 18,000MW HEP station inside the dam.
  • Cost more than $38bn.
• Benefits of Three Gorges Dam:

  • 50mn protected by flooding like 1998.
  • Millions of hectares of farmland protected and provided with irrigation.
  • 13mn people's water supplies are now secure.
  • 10% of China's electricity is produced by the dam.
  • 10,000 tonne ships are now able to navigate the river up to Chongqing.
  • 500% increase in river expected and big boost in economic growth.
• Disadvantages of Three Gorges Dam:

  • 150 towns and 1300 villages flooded by reservoir.
  • 1.2mn people displaced.
  • Reservoir is heavily polluted by toxins from flooded mines adn factories.
  • Damaged the local ecosystems.
  • River is laden with silt, which will reduce reservoir capacity.
  • 1000 cultural sites flooded.
• Afforestation: Soft Engineering

  • Trees encourage interception, evapotranspiration and interception.
  • Forested areas have less soil erosion - reduces silt ending up in river.
  • Trees can be harvested for food, fodder, fuel and timber.