Floods are an overflow of water that submerges land and usually happen because of a large amount of rainfall, saturated soil, and/or the capacity of the body of water is exceeded: Often floods are seasonal in nature, coming after Spring rains.

Floods also occur in rivers, when flow exceeds capacity in certain areas of the river channel.

Floods have impacted society for centuries because people like to live near water and water transportation.

In certain parts of the world, typically those with regular monsoon conditions, flooding is a regular seasonal issue

Suggested graphics: http://www.kidcyber.com.au/IMAGES/Floods4.jpg

Types of Floods -- The flood type depends on the geographic location of the body of water and its tendencies:

Areal flooding happens when flat, low-lying areas cannot absorb any more water

River floods occur when the river cannot carry away all the extra water and the river overflows

Coastal floods are usually caused by harsh weather blowing waves onto land.

Flash Flooding is a quick flood caused by a sudden cloudburst or thunder storm. Often these happen in mountainous areas with steep slopes.

Flooding from Human Action occurs when an artificial structure like a dam fails, or levees or pipes burst or are poorly constructed.

Suggested graphics: http://www.sciencemediacentre.co.nz/wp-content/upload/2011/02/flood.jpg

Flood Causation -- Flood can occur for a number of reasons, which makes them incredibly hard to predict and prepare for, particularly since humans tend to congregate around water.

Water from storms can no longer be absorbed into the soil; either pools or runs to lower elevation.

Heavy snowfall pack in areas followed by strong Spring/Summer rains

Intense precipitation -- thunderstorms, etc. Or release from a landslide or glacier

In estuaries caused by tidal surges from storm-force winds

Tsunami's or hurricanes -- storm surges

Catastrophic from dam breakage, earthquake or volcanic eruption -- also called outburst flooding

Suggested graphics: http://www.cnn.com/video/weather/2011/01/12/vo.sri.lanka.floods.slrc.640x360.jpg

Effects of Flooding, Part 1

Primary effects -- damage to structures, bridges, buildings, sewage system, roadways, canals

Floods have had a major impact on human society for centuries

Floods disrupt society completely; including social structures and economics

Transportation issues affect surrounding areas

People may need to be evacuated and rehoused for a time

Disruption in entire socio-culture template

Suggested graphics: http://news.xinhuanet.com/english/2008-06/15/xin_5020605152044156235937.jpg

Effects of Flooding, Part 2

Secondary effects -- as the water recedes or damage due to pressure, weather, etc.

Secondary effects may last for months, even years

Water supplies -- water may become contaminated

Potable water becomes rare

Spread of waterborne diseases (lack of sanitation, standing water)

Crops and food supplies ruined, sometimes entire harvests

(e.g. Katrina)
Inadequate disaster planning and evacuation procedures

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Flood Control, Part 1

Humans have been trying to control floods for thousands of years. However, some flooding, particularly along the great river valleys (e.g. Nile) were the reason agricultural activities flourished and civilization developed

There is a balance between the regular flooding of river areas and catastrophic flooding

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Flood Control, Part 2

Dams and reservoirs are designed to aid in flood protection and control. They do this by controlling water levels and allowing water to flow as needed, but to protect lower elevations by storing water behind the dam wall.

River defenses -- Levees, bunds, reservoirs and weirs (low head dam) are all used to prevent rivers from bursting

Coastal defense -- sea walls, barrier islands, tide gates, enhancing beach areas

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Flood Control, Part 3

Different regions have adapted flood control based on their economic wealth, type and frequency of flooding, and the density of population near flood-prone areas.

Americas -- Usually miles of levees, flood gates, and drainage systems

Asia -- Some building of massive dams, but deforestation…