- 1 Types of Flood
- 2 Causes of Flood
- 3 Hazards Associated with Flood
- 4 Flood Mapping in Bangladesh
- 5 Flood History of Bangladesh (1954-2016)
- 6 Flood Forecasting
- 7 Measures of Flood
- 8 References
Flood is a temporary covering by water of land which is not normally covered by water. This shall include floods from rivers, mountain torrents, Mediterranean ephemeral water courses, and floods from the sea in coastal areas, and may exclude floods from sewerage systems.
In shortly we can define flood as an abnormal progressive rise in the water level of streams or rivers which may result in overflowing.
Types of Flood
Floods are mainly five types-
- River / Monsoon flood
- Flash flood
- Ponding flood
- Coastal flood
- Urban flood
River / Monsoon flood
When river water rises and spills over the bank of the river and covers some area with river water which is normaly dry land this flood is called as river / monsoon flood.
Flash flood is a sudden flood in a low-laying area, most commonly caused by periods of perticularly heavy rainfall. Generally happens in the valleys of the hilly areas.
Ponding is a type of flooding that can happen in relatively flat areas. Rain water falling in an area is normally stored in the ground, in canals or lakes, or is drained away. When more rain water enters a water system than can be stored, or can leave the system, flooding occurs.
When coastal area is covered by sea which is normally dry land is called coastal flood.
Urban flooding is specific in the fact that the cause is a lack of drainage in an urban area. Flooding in urban areas can be caused by flash flood, or coastal flood, or river flood.
Causes of Flood
There are several causes of floods and differ from region to region. Some of the major causes are-
- Heavy monsoon rainfall.
- Low general topography.
- Heavy siltation of the river bed reduces the water carrying capacity of the rivers/stream.
- Blockage in the drains lead to flooding of the area.
- Landslide blocking the flow of the stream.
- Construction of dams.
- Snow melting.
- Rise of mean sea level.
- Flow tide in the Bay of Bengal.
- Deforestation and flood protection projects in the upper catchments outside Bangladesh.
- Greenhouse effect.
Hazards Associated with Flood
A dangerous condition or threat for causing injury to life or damage to property or the environment is called hazard. Flood isn’t the stander condition of environment. It is threated not only human but also environment. Some effect of flood hazard is given below-
- Displacement of Families in the river banks
- Destruction of private property on the river banks
- Destruction of Biodiversity on the river banks
- Disruption of Transport and communication systems
- Destruction of drainage and sewage system
- Eroding of river banks
- Adverse effect on Public Health
Flood Mapping in Bangladesh
Flood History of Bangladesh (1954-2016)
|Year||Flood Affected area||Year
|Flood Affected area||Year||Flood Affected area|
Source: Annual Flood Report, Flood Forecasting & Warning Centre, Bangladesh Water Development Board.
Flood forecasting is the use of forecasted precipitation and streamflow data in rainfall-runoff and streamflow routing models to forecast flow rates and water levels for periods ranging from a few hours to days ahead, depending on the size of the watershed or river basin.
“Yellow” when the river is flowing in Low Flood: when river water level is at or above WL but below DL.
” Pink” when the river is flowing in Moderate Flood: when river water level is at or above DL but below level which is 0.5 m below HFL.
“Orange” when the river is flowing in High Flood: when the river water level is within 0.5 m of HFL and below HFL.
“Red” when the river is flowing in Unprecedented Flood: when the river water level is at or above HFL. HFL is updated on a yearly basis before start of the flood season.
Flood forecasting can be divided into two categories:
- Flood forecasting in the rivers caused by upstream rise of river stage as well as rainfall in the basin.
- Overland flow from upstream.
Measures of Flood
Floods are natural phenomena which cannot be prevented. But we can reduce flood damage. We found two ways to preventive and measures of flood damage. These are-
- A measure to control the physical process of flooding. It also prevents inundation.
- Protects vulnerable areas up-to certain level of flooding.
- Clear the river and water flow channel.
- Construction culvert to save road during flood.
- Planting trees near the river bank to save from erosion.
- Sand bags and Stone are thrown at river bank to protect bank from erosion.
- Construction dam to protect town from flood by changing the way of river.
- Flood forecasting.
- Early warning of flood.
- Flood insurance.
- Changes in cropping pattern.
- Know about the safe zones during flood.
- Emergency communication system during flood.
- Annual Flood Report by Flood Forecasting & Warning Centre, Bangladesh Water Development Board.
- American Journal of Civil Engineering. 2014; 2(1): 8-11 Published online February 20, 2014 (http://www.sciencepublishinggroup.com/j/ajce)
- A Review of Flood Management in Bangladesh: A Case study of 2004 Flood By Ainun Nishat, Country representative, IUCN-The World Conservation Union
- Article on Flood by Institute of Environmental Engineering, Technical University of Košice.
- Article on Natural Hazards and Earth System Sciences (2004) 4: 295–308 SRef-ID: 1684-9981/nhess/2004-4-295.