Natural Disasters : Floods

Definition

• A flood is an overflow of water that submerges land that is usually dry.

Causes of Flood

1. Natural Causes
   • Rainfall
     • Intense rainfall triggers the overflow of rivers.
     • This is most common in the monsoon season.
   • Snowmelt
     • The snow and glaciers in the mountains melt due to rising temperatures and flow down into the rivers and streams.
     • This can increase the water level and cause floods downstream.
   • Cyclones
     • A climatic event like a cyclone generates heavy rainfall that results in floods.
     • It is common when EL Nino is weak.
   • River Overflow
     • Excessive rainfall in river catchments or concentration of runoff from the tributaries, and rivers carrying flows in excess of their capacities.
     • Blocking of tributaries of rivers due to various factors like landslides.
2. Manmade Causes
   • Collapse of dams 
   • Illegal construction of buildings in the catchment areas of rivers 
   • Rapid urbanisation
   • Deforestation

Types of Floods

• Coastal Floods: Coastal floods occur when strong winds or storms move towards the coast during high tide.
• Flash Floods: Flash floods occur in hilly areas in limited space and this type of flood is caused by sudden heavy rainfall or snow thaws.
• River Floods: River floods occur due to the inflow of water from heavy rainfall, snowmelt, or powerful storms.
• Pluvial Floods: Pluvial floods occur in areas that cannot hold rainwater and end up forming puddles and ponds. These types of floods are evident in rural areas.
• Urban Floods: When the drainage system of urban areas fails to absorb rainwater, it creates urban floods.

Impacts of Floods

• Human Loss and Property Loss – Every year, millions of people become homeless and washed away due to floods.
• Spread of Communicable Diseases – Waterborne diseases like cholera, typhoid fever, hepatitis, and leptospirosis spread in flood-affected areas. Floods also lead to vector-borne diseases, transmitted through parasites and pathogens such as mosquitoes. As a result, the health of flood victims deteriorates.
• Destruction of Crops –  Every year, floods destroy a large number of crops.
• Loss of Livestock – Like humans, livestock also gets displaced during floods and die due to the loss of their habitats.
• Disruption of Communication Link and Transportation –  Floods cause damage to transportation links such as bridges, rail, power plants, etc., thus causing communication disruption in those areas.
• Economic and Social Disruption –  The economy comes to a standstill as people are forced to move to another place, and the revival of this situation takes time.

NDMA Guidelines for Flood Management

Mitigation (Post – Flood Management)

• Rescue Operations
• Speedy restoration of the transport system
• Supply of safe drinking water
• Repair of power, telephone, and sewerage lines
• Supply of food, shelter, and clothing
• Survey to assess the loss and compensation
• Rehabilitation of properties
• Desilting and dewatering of inundated areas
• Contingency Plans for the agriculture sector