types of floods ( 28-04-2011 L: 2)

The common flood types in Bangladesh are:

Flash flood:  Flash flood in the eastern and northern is characterized by a sharp rise followed

 by a relatively rapid recession often causing high flow velocities that damage crops and property.

Local floods: Due to high localized rainfall of long duration in the monsoon season often generates water volume in excess of the local drainage capacity, causing localization floods due to drainage congestion.

Monsoon flood: Generally rise slowly, spilling through the bank of the rivers and distributaries causes the most extensive flow damage, particularly when the three major rivers simultaneously.  

Floods due to storm surges: In the coastal areas of Bangladesh, which are generates by tropical cyclones are predominant during the post monsoon (Oct ~ Nov) and pre-monsoon (Apr ~ Jun) period.

Floods arising from failure of dam: Due to poor maintenance and exceptionally high precipitation. These cause a surging water front travelling with high velocity causing destruction of properties and loss of life.

Causes of flood in Bangladesh: There are two distinct seasons, a dry season (Nov~ Apr) and the wet (flood) season (Jun ~ Sep) over 80% of the rainfall occurs during the monsoon or rainy season also known as flood season. The normal annual rainfall of the country varies approximately from 1200mm in the west to over 5000mm in the east. Long periods of steady rainfall persisting over a several days are common during the monsoon, but sometimes local high intensity rainfall of short output also occurs. Most of the country consists of a huge flood plain and delta. 75% of Bangladesh is less than 10m above sea level.

Floods in Bangladesh occur for number of reasons: The main causes are excessive precipitation, low topography and flat of the country, but others include:

v  The geographic location and climatic pattern: Bangladesh, is located the foot of  the highest mountain range in the world, the Himalayas, which is also the highest precipitation zone in the world. This rainfall is caused by the influence of the southwest monsoon Cherapunje, highest rainfall in the world, is located a few kilometers north west of the Bangladesh border.