Causal phenomena

Naturally occurring flash, river and coastal flooding from intense rainfall or innundation associated with seasonal weather patterns
Human manipulation of watersheds, drainage basins and floodplains

General characteristics

Flash floods - Accelerated runoff, dam failure, breakup of ice jam
River floods - Slow buildup, usually seasonal in river systems
Coastal floods - Associated with tropical cyclones, tsunami waves, storm surges
Factors affecting degree of danger: depth of water, duration, velocity, rate of rise, frequency of occurrence, seasonality

Predictability

Flood forecasting depends on seasonal patterns, capacity of drainage basin, flood plain mapping, surveys by air and land. Warning possible well in advance for seasonal floods, but only minutes before in case of storm surge, flash flood, or tsunami.

Factors contributing to vulnerability

Location of settlements on floodplains
Lack of awareness of flooding hazard
Reduction of absorptive capacity of land (erosion, concrete)
Non-resistant buildings and foundations
High risk infrastructural elements
Unprotected food stocks and standing crops, livestock
Fishing boats and maritime industries

Typical adverse effects

Physical damage - Structures damaged by washing away, becoming inundated, collapsing, impact of floating debris. Landslides from saturated soils. Damage greater in valleys than open areas.
Casualties and public health - Deaths from drowning but few serious injuries. Possible outbreaks of malaria, diarrhea and viral infections.
Water supplies - Contamination of wells and groundwater possible. Clean water may be unavailable.
Crops and food supplies - Harvests and food stocks may be lost to innundation. Animals, farm tools and seeds might be lost. Floodplain mapping. Land use control

Possible risk reduction measures

Flood control (channels, dikes, dams, flood-proofing, erosion control)

Specific preparedness measures

Flood detection and warning systems
Community participation and education
Development of master plan for floodplain management

Typical post-disaster needs

Search and rescue; medical assistance; disaster assessment; short term food and water supplies; water purification; epidemiological surveillance; temporary shelter

Impact assessment tools

Damage survey forms; aerial surveys