Flooding in Chang Jiang Causes

Why flooding occurs? Discharge? Discharge? Velocity? Velocity? Load? Load? Carrying capacity of river/lakes? Carrying capacity of river/lakes?

Why discharge increases?

Why so much rainfall? Monsoon climate Monsoon climate Heavy + prolonged in summer Heavy + prolonged in summer Monsoon wind + typhoons (tropical cyclones) Monsoon wind + typhoons (tropical cyclones)

Results of heavy rain Rapid runoff Rapid runoff Increasing river discharge Increasing river discharge Beyond the bankfull capacity Beyond the bankfull capacity

Why velocity decreases?

Relief of the lower course Flat Flat Small gradient Small gradient With meanders With meanders Favour deposition Favour deposition

Why more load + discharge?

Confluence point

Drainage characteristics at confluence point Velocity decreases Velocity decreases Discharge increases Discharge increases

Silt content Yichang section: 0.83 kg/m ³ (2002) Yichang section: 0.83 kg/m ³ (2002) Pingshan section: 1.54 kg/m ³ (2002) Pingshan section: 1.54 kg/m ³ (2002) (source: Three Gorges Probe)

Should human be responsible for flooding? Deforestation Deforestation Soil erosion Soil erosion More load More load Silting Silting Reduction in carrying capacity of river Reduction in carrying capacity of river Dyke maintenance  leakage + collapse Dyke maintenance  leakage + collapse

Why is there deforestation? Careless farming practices Careless farming practices Over-grazing Over-grazing Over-cultivation Over-cultivation Timber production Timber production mining mining

Results of deforestation Reduce rate of infiltration Reduce rate of infiltration Increase surface runoff Increase surface runoff Soil dries out easily Soil dries out easily Soil erosion Soil erosion Deposition takes place Deposition takes place Raise river bed Raise river bed Silting Silting

Conclusion: causes of flooding Physical factors Physical factors Human factors Human factors