1. Managing River Floods Natural Physical Causes of Floods
Human Causes of Floods
Factors that increase the risk of floods becoming a disaster
Flood management techniques

2. Natural Causes of floods
Prolonged periods of heavy rainfall
Over a long period of time meaning that soils become saturated.
High intensity rainfall meaning that the water cannot infiltrate the soil or drain away quickly.
Heavy rainfall can be very localised leading to local ‘flash floods’ as in the above picture.

3. Natural Causes of floods
Extreme weather systems such as tropical cyclones or thunderstorms.
Extreme weather tropical cyclones (aka hurricanes) are characterised by heavy rainfall. This exceeds soil’s infiltration rate resulting in overland flow and sudden flash floods

4. Natural Causes of floods
Sudden snow or ice melt
Sudden snow melt results in heavy runoff. This increases the risks of floods as the meltwater flows into river channels.

5. Natural Causes of floods
Rain falling on saturated soil.
When soil is saturated, overland water flow into rivers occurs.

6. Natural Causes of floods
Large areas of low lying flat land
When the land is flat the flood waters spread extensively causing widespread damage.
Eg Ganges Delta - Bangladesh

7. Natural Causes of Floods
High discharge where two or more tributaries meet at confluences
Rising tides preventing the discharge of water into the sea may lead to ‘back-up’ the river.

8. Human causes of floods Large scale deforestation
Change in land use from woodland to farmland
Large scale ‘urbanisation’ into the drainage basin.
Poorly constructed/maintained drainage system
Building on floodplains
Ineffective or poorly maintained flood protection scheme.
Other forms of river management
Untimely release of water from dams/dam failure, earthquakes, landslides or storms
Sedimentation of river channels due to soil erosion

9. Factors that increase the risk of a flooding disaster
Lack of awareness of the flood risk.
Lack of preparation.
Lack of disaster planning – Inadequate evacuation, emergency transport
Lack of emergency supplies – medication, water purification tablets.
Contamination of drinking water
Loss of power supplies/fuel.
Disruptions or damage to transport infrastructure.
Damage to crops, loss of livestock
Dead bodies and animals increase risk of disease.
Flooding of key buildings eg hospitals.

10. Flood Management Techniques
Planning regulations – control building on flood plains.
Build flood defences
Re-afforestation
Diversionary river channels or spillways.
Relocation of high risk settlements
Drainage basin modelling
Flood forecasting and development of warning systems.
Temporary flood defences eg sand bags, gates.
Flood shelters
Buildings flood proofed eg built on stilts.
River restoration projects
Emergency planning
Government and or overseas AIDS.