Friday, August 6, 2010

Types of floods

Major Flood Prone Area across the World

1. Slow-Onset Floods

  • Slow-Onset Floods usually last for a relatively longer period, it may last for one or more weeks, or even months. As this kind of flood last for a long period, it can lead to lose of stock, damage to agricultural products, roads and rail links.

  • Slow onset floods like those that hit Bangladesh every year can also be lethal but tend to give people much more time to move to higher ground. When deaths occur, they are much more likely to be due to disease, malnutrition or snakebites. In 2007, floods in China displaced tens of thousands of snakes into neighboring areas, increasing the risk of attacks. Slower floods are also less likely to sweep away property, although it may still be damaged or destroyed. Areas are likely to remain under water for much longer. In India in 2007, some were unable to return to their homes for months.

2. Rapid-Onset Floods

  • Rapid-Onset Floods last for a relatively shorter period, they usually last for one or two days only. Although this kind of flood lasts for a shorter period, it can cause more damages and pose a greater risk to life and property as people usually have less time to take preventative action during rapid-onset floods.

3. Flash Floods

  • Flash Floods may occur within minutes or a few hours after heavy rainfall, tropical storm, failure of dams or levees or releases of ice jams. And it causes the greatest damages to society.

Flooding can also be divided into different categories according to their location:
1. Coastal Floods
  • Coastal Floods usually occur along coastal areas. When there are hurricanes and tropical storms which will produce heavy rains, or giant tidal waves created by volcanoes or earthquakes, ocean water may be driven onto the coastal areas and cause coastal floods.

2. Arroyos Floods
  • A arroyo is river which is normally dry. When there are storms approaching these areas, fast-moving river will normally form along the gully and cause damages.

3. River Floods
  • This is the most common type of flooding. When the actual amount of river flow is larger than the amount that the channel can hold, river will overflow its banks and flood the areas alongside the river. And this may cause by reasons like snow melt or heavy spring rain.

4. Urban Floods
  • In most of the urban area, roads are usually paved. With heavy rain, the large amount of rain water cannot be absorbed into the ground and leads to urban floods.

cloud-burst-ireland-jim-gola.jpg (472×700) What is a cloudburst?A cloudburst is sudden copious rainfall. It is a sudden aggressive rainstorm falling for a short period of time limited to a small geographical area.

Meteorologists say the rain from a cloudburst is usually of the shower type with a fall rate equal to or greater than 100 mm (4.94 inches) per hour.

Generally cloudbursts are associated with thunderstorms. The air currents rushing upwards in a rainstorm hold up a large amount of water.

If these currents suddenly cease, the entire amount of water descends on to a small area with catastrophic force all of a sudden and causes mass destruction. This is due to a rapid condensation of the clouds.

They occur most often in desert and mountainous regions, and in interior regions of continental landmasses.

During a cloudburst, more than 2 cm of rain may fall in a few minutes. They are called 'bursts' probably because it was believed earlier that clouds were solid masses full of water. So, these violent storms were attributed to their bursting.

Record Cloudbursts

1 minute
1.9 inches (48.26 mm)
Leh, Jammu & Kashmir, India
06 August, 2010
1 minute
1.5 inches (38.10 mm)
Barot, Himachal Pradesh, India
26 November, 1970
5 minutes
2.43 inches (61.72 mm)
Port Bells, Panama
29 November, 1911
15 minutes
7.8 inches (198.12 mm)
Plumb Point, Jamaica
12 May, 1916
20 minutes
8.1 inches (205.74 mm)
Curtea-de-Arges, Romania
7 July, 1947
40 minutes
9.25 inches (234.95 mm)
Guinea, Virginia, USA
24 August, 1906


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