Causes of Flooding Flashcards
Deforestation
- Reduced interception, water direct onto ground faster
- increased risk of saturation, so less infiltration
- more surface runoff and higher discharge
- Increased soil erosion means rivers have greater load
- less transpiration so greater discharge
Climate Change
- Global temps increase by 1.2 deg. C
- High sea temps. increase frequency and intensity of hurricanes.
- Rising sea levels increases risk of low land flooding
River management
Raising levees can increase severity of flooding downstream as well as preventing water from flowing back into river channel
Precipitation
- Intensive levels of precip can saturate ground
- promotes surface runoff
- Also occurs when precip. rate > infiltration capactiy
Snowmelt
- Melting snow provides rapid influx of water into river system. Soil can be still frozen
- more water in rivers than can be held
Geology (rock type)
- Permeable rocks (chalk) allow greater percolation
- Impermeable rocks (granite) reduce infiltration
Soil
Clay soils have low infiltration capacities and therefore promote surface runoff and flooding. Sandy soils have infiltration capacities and therefore reduced flood risk.
Vegetation
Greater vegetation cover increases interception, reducing peak discharge and increasing lag time
Climatic hazards
Cyclones in Bangladesh, hurricanes in the Gulf of Mexico as well as deep low pressure systems in the mid latitudes bring abnormal amounts of precip.
Drainage basin characteristics
Circular basins increase the flood risk as all rain that falls in the basin takes the same amount of time to reach channel. Opposite for long and thin. A basin with lots of tributaries can carry water quickly to channel, increasing discharge
Urbanisation
55% of world’s population live in urban areas. Greater demand for housing results in construction on floodplains. Impermeable surfaces increase surface runoff.
Agriculture
Compacting of soil, reducing infiltration capacity by ploughing/grazing. Overgrazing results in soil erosion
