Lecture 9: Understanding and managing flood risk 2

Question 1

Types and causes of flood

Answer 1

Coastal flooding – high river flows combined with high tides, low pressure systems, sea surge

River flooding – river overtops its banks to flood the surrounding land as a result of prolonged and extensive rain, snowmelt, blockage with debris

Flash flooding – very rapid flooding as a result of high intensity rainfall, failure of dam or flood defence, or insufficient drainage esp. in urban areas.

Groundwater flooding – groundwater levels rise as a result of prolonged rainfall or changing abstraction. Floods basements, roads.

Sewer flooding – when sewers fail or cannot cope with rainfall

Question 2

Groundwater flooding

Answer 2

A few hundred thousand properties in UK

Rising groundwater levels during wet periods

Often not dramatic but still costly and inconvenient

Question 3

Causes of enhanced flood risk

Increased risk:

Answer 3

Urbanisation, less urban green space/drainage

Deteriorating urban wastewater systems/blocked drains

Agriculture and agricultural practices

Climate change (wetter winters)

Climate change (increased high rainfall events)

Loss of wetlands and floodplain (reduced storage)

Sea level rise

Question 4

Causes of enhanced flood risk

Increased exposure

Answer 4

More infrastructure, housing, people

Increased building in high risk areas

Greater population densities especially at the coast

Question 5

Causes of enhanced flood risk

Increased vulnerability

Answer 5

Poverty

Urbanisation & higher dependence on
infrastructure

Question 6

Land use impacts:

Answer 6

Runoff enhancement (compaction)

Soil erosion

Debris blockage

Responses: check dams, buffer strips to slow down and store water