Flood Hazards

FLOOD HAZARDS

Among the natural hazards, flood is the most widespread.

The accumulation of large quantity of water at a place or the flow of more water than that can be handled by the drainage of the area is known as flood.

Factors resulting floods

The occurrence of flood at any particular place depends on the following factors.

• Climatic conditions of the area

• Nature of the collecting basin

• Nature of the streams, soil and vegetative cover

• Rate of melting of snow,

• Amount of rainfall received.

Types of Floods

There are '3' types of floods

(i) Flash flood

(ii) River flood

(iii) Coastal flood

 (i) Flash Floods

These occur within hours of heavy rainfall. They are usually associated with towering cumulus clouds, severe thunderstorms and tropical cyclones or the passage of cold weather fronts.

Flash floods may also be caused by dam failure or other river obstructions.

(ii) River Floods

River floods are caused by precipitation over large catchment areas or by melting of snow or sometimes both.

They take place in river systems with tributaries that may Cover or drain large geographical areas. They involve many independent river basins.

These floods normally build up slowly and may continue for days or weeks as compared to flash floods.

The amount of flooding depends on factors such as ground conditions (moisture, vegetation cover, and depth of snow) and size of the catchment basin.

 (iii) Coastal Floods

Coastal floods are associated with the cyclonic activities such as hurricanes, tropical cyclones, etc. They are often aggravated by wind-induced storm surges along the coast.

Heavy rains over a large geographic area produce extreme flooding in coastal river basins, similar to river floods.

Causes of Floods

1. Heavy rain for a very short period result in floods.

2. River can overflow their banks to cause flooding, as it flows downstream to the adjacent low lying areas.

3. Sea water can be carried by massive winds & hurricanes on to dry coastal lands and cause flooding.

4. Excess of water held up in the dam can cause it to break and overflow the area. Excess water can be released from the dam to prevent it from breaking and that can also cause floods.

5. Heavy snow over the winter stays unmelted for sometime. This ice suddenly melts when the temperature rises, resulting in flow of water in to places that are dry. This is called snow melt flood.

Effects of Flood Hazards

Floods can result devastating consequences and effects on the economy.

Primary hazards

Primary hazards are the effects of floods due to direct To aysh Tol contact with the flood waters.

• With greater velocities, flood streams are able to carry larger objects such as houses, bridges and automobiles.

• Humans can get caught in the high velocity flood waters asitivi and can be drowned in the water.

• Floods can cause erosion, erosion can weaken bridges, and buildings causing their collapse.

• Flooding of farmland can result in loss of crop, livestock, pets and other animals.

Secondary Hazards

Secondary hazards are those that occur because of primary

• Drinking water gets polluted if sewage treatment plants are in the flooded area. This contamination can result in disease and other health issues.

• Transportation systems can be affected and as a result ed as food supplies and aid can be delayed. This has resulted brain starvation even in developed countries.

Tertiary or Long term Hazards

• Long term changes bua

• Destruction of wildlife habitat.

• Sediment deposited during flooding may leave farm land in poor condition.

Methods of flood prevention

The intensity of flood can be minimized using the following measures.

Plantation on Slopes

Plantation helps in regulating river flow and controls soil erosion.

Drainage Management

Improvement of channels by removing debris and sediments helps in regulating the rate of river flow.

Floodplain Zoning

Flood plains can be managed by dividing them into different temporal plots. This is commonly referred to as flood-plain zoning.

Forecasting

Possible damage can be minimized by forecasting the occurrence of floods and warning the people about the possible danger.