River Chang Jiang China

• Physical (environmental) causes of flood

  • Snowmelt in the Himalayas
  • Summer monsoon rains
• Human causes of flood

  • Rapid increase in urban population
  • Factories built on floodplain
  • Deforestation
  • Mismanagement of deforested land
  • Canalisation
• Effect on population

  Urban population of China has experienced a rapid increased. Many cities are positioned besides the river → More people & property are at risk of getting affected than in the past.
• Effect on infrastructure

  • Factories have been built in the village communes to provide jobs for the country folk. Many of these are on the floodplain & are not as well protected from floods, compared to those in the cities → These factories & workers' houses are at risk.
  • More buildings on the floodplain = less room for the floodwater → flood levels rise higher.
• Effect of deforestation on flood

  If in source of the river = less interception from vegetation → less evapotranspiration & infiltration. Overall leading to more surface run-off & greater flood peaks.
• Mismanagement of deforested land

  E.g Overgrazing; It has led to soil erosion & more silt being washed into the river channel → less room for the water & flood levels rise.
• Canalisation


  • This is the process of introducing weirs and locks to a river so as to secure a defined depth suitable for navigation.
  • This is applied to a river (the canalisation of a river) to improve river transport & even straightens the river → speeding the water's flow → reducing lag time → increasing the flood peak.
• Flood protection


  • Embankments have restricted the river. Meaning the river can hold more water but when the banks break, the flooding is more deadly & rapid. → People have less time to escape.
  • Back in the day, Dongting & Poyang Lakes near Wuhan acted as safety valves. Floodwater from the river was diverted into these lakes → reducing the potential flood peak.
  • More recently, farmers have been reclaiming polders from the lakes to create new farm land. Meaning much smaller lakes & less room in the lakes for floodwaters → rising flood peak levels.
• The monsoon rains in China lasted a month longer. (Were not more intense) At one point reaching 45 metres tall.
• Consequence/Sacrifice

  • Wuhan, the largest city in the monsoon-affected region, needed some form of protection. They accomplished this by intentionally breaching many of their river flood prevention embankments.
  • Large areas of the contryside were flooded as a result, houses & factories destroyed in the village communes.
  • 14 million people = homeless for months; untill could be repaired/replaced
  • Unemployment rates increased. while factories getting repaired
  • Great thickness of sticky clay was deposited onto the fertile fields; had to be removed before farming could re-commerce. → inconvenience for people cleaning up
• What lakes near Wuhan acted as valves?

  Lakes Dongting and Poyang