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State government report on Chennai’s flood:

GS Paper 3

Topics Covered: Disaster Management.

 

Context:

Tamil Nadu state government has released a report on the action taken by the government with regard to measures to prevent recurrence of flooding.

  • The report was in response to the National Green Tribunal (NGT) registering a suo motu. The court had done so after newspapers widely reported areas in the city being flooded in addition to an overflow of sewage November 30, 2020.

 

What has the report said?

Causes for flooding:

  1. Encroachments, faulty drainage systems and tampering of natural course of water had made the megapolis prone to flooding every year.
  2. Rapid urbanisation of Greater Chennai and its peri-urban areas had led to massive changes in land use patterns, as residential areas had sprung up in farmlands.
  3. The changes in land use patterns were done without making the required changes for a proper drainage system to manage the flow of surplus water from traditional tanks as well as flood waters from catchment areas.
  4. Irrigation tanks were choked with waste, slush and debris, obstructing the flow of flood water. This also reduced the water-absorbing and groundwater recharging capacity of the marsh.

 

Measures suggested:

Chennai needs an integrated flood management system with proper facilities to drain excess rainwater and desilt channels to prevent floods.

  • The report recommended an integrated road and street side storm water drainage network, straight cut diversion channels, macro storm water drains, check dams, barrages and anicuts as part of such a system.

 

Urban floods in India- an overview:

Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers.

  • In many Indian cities, urban floods have become a frequent phenomenon in recent years.

 

Unscientific urbanization leading to Urban floods:

Natural factors:

  1. Increasing downpour.
  2. Cyclonic storms and thunderstorms.
  3. occurrence of high tides impeding the drainage in coastal cities.

 

Anthropogenic factors:

  1. Concretization.
  2. Wiping out of the wetlands.
  3. Poor Water and Sewerage Management.
  4. Encroachment and Illegal constructions.
  5. Deforestation.

 

Administrative factors:

  1. Lack of flood control measures.
  2. Multiple authorities in a city but owning responsibility by none.

 

Measures needed:

Structural Measures:

  1. Conservation of wetlands in urban areas like lakes, ponds, streams.
  2. Construction of differential slope along sidewalks, roads to drain excess water into reservoirs.
  3. Strengthening of Storm water drainage system.
  4. Pre-monsoon desilting of all major drains to be completed by March 31 each year.
  5. Every building in an urban area must have rainwater harvesting as an integral component of the building utility.
  6. Concept of Rain Gardens to be incorporated in planning for public parks and on-site storm water management for larger colonies and sites those are to be developed.
  7. Suitable interventions in the drainage system like traps, trash racks can be provided to reduce the amount of solid waste going into the storm sewers.

 

Non-structural Measures:

  1. National Hydro-meteorological Network as per NDMA is needed for all urban cities in India.
  2. Flood hazard assessments should be done on the basis of projected future scenarios of intensities and duration of rainfall and land use changes.
  3. Better forecasting of rainfall events; timely dissemination of information to the mass- ‘Nowcasting’ alerts or real-time weather updates.
  4. Restrict encroachments in natural drainage areas; clearance of river beds, proper implementation of Coastal Regulation Zone rules.
  5. Provisions for flood-proofing of buildings
  6. Storm water pollution control, i.e. source is controlled by imposing quality standards for wastewater and solid waste disposals in urban environments.

Sources: down to earth.