Flood is the one of the natural catastrophe this world witness every year. Thousands of people lose their life and properties.
Flood is the irregular, turbulent flow of water that sweeps away any thing that comes in the way. Flood is always turbulent, non uniform and unsteady in nature.
Flood is seen in the area with gradual decrease in bed slope. In the highly stepped area the discharge velocity is high which ultimately donot let the water to cover the large area as it is forced to move down due to gravity. The normal flow depth is less than the critical flow depth, thus the upstream side has high normal flow depth than the downstream side.
In the plain zone the discharge velocity is very low. As a result the normal flow depth is much higher than the critical flow depth in comparision to the stepped bed. This results in increase in the normal flow depth in the downstream area. To maintain the low energy level water mass is forced to move to the region with low energy level resulting in large effected area.
There are many reason behind the flooding. They are listed below:
- Increase in volume of water in upstream side, discharge velocity being almost same in the downstream side.
- GLOF( Glacier lake outbrust flood)
- Poor management of water canals and sewers in city areas.
- Deforestation etc.
Consequences of flood:
- Loss of life and property.
- Erosion of soil mass.
- Foundation of structures are carried away that may make them unstable.
- Ponding for long interval may cause quick sand condition in cohison less soil.
- May result in liquefaction and subscidence.
- Cutting of the river bank resulting in formation of oxbow lake and so on.
Mitigating ways to control the flood:
- Proper discharge management structures can control the flood in some extend.
- Afforestation.
- Regular examination of Glacier lakes and public should be made aware of cause, consequences and way to eradicate it .
- Proper management of sewage and drainage system.
- River can be diversed during flooding seasons to distribute the water mass.
- Embankment can stop the erosion of soil and prevent large volume to across the area.
Positive aspects of flood:
- The deposition of eroded soil mass makes a new landmass.
- The flood water carries the dead and decomposed matter making soil more fertile.
- Flood water recharge the ponds and lakes.
- Formation of new geological structures.
- Carries away the waste materials and deposit to another area.
- People can find new stuff that is carried by water mass.
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