13. Urban Floods

What is urban flooding?

  • Flood is defined as “an overflow of a large body of water over areas not usually inundated”. Thus, flooding in urban areas is caused by intense and/or prolonged rainfall, which overwhelms the capacity of the drainage system.

  • Urban flooding is significantly different from rural flooding- urbanization increases flood risk by up to 3 times, increased peak flow results in flooding very quickly. Further, it affects large number of people due to high population density in urban areas

Causes of urban flooding

Meteorological Factors:

  • Heavy rainfall, cyclonic storms and thunderstorms

Hydrological Factors:

  • Overbank flow channel networks, occurrence of high tides impeding the drainage in coastal cities.

Anthropogenic Factors:

1.Unplanned Urbanization:

Unplanned Urbanization is the key cause of urban flooding. A major concern is blocking of natural drainage pathways through construction activity and encroachment on catchment areas, riverbeds and lake beds.

Some of the major hydrological effects of urbanization are:

  • Increased water demand, often exceeding the available natural resources;

  • Increased wastewater, polluting rivers and lakes and endangering the ecology-

  • Destruction of lakes is a major issue in India cities. Lakes can store the excess water and regulate the flow of water. However, pollution of natural urban water bodies and converting them for development purposes has increased risk of floods.

  • Reduced infiltration due paving of surfaces which decreases ground absorption and increases the speed and amount of surface flow.

  • Reduced groundwater recharge, increased use of groundwater, and diminishing base flow of streams.

  • Increased peak flow

2.Climate Change:

  • Climate change due to various anthropogenic events has led to extreme weather events.

3.Poor Solid Waste Management System:

  • Improper waste management system.

  • Clogging of storm-water drains because of silting, accumulation of non-biodegradable wastes and construction debris.

4.Drainage System:

  • Old and ill maintained drainage system is another factor making cities in India vulnerable to flooding.

Impact of Urban Flooding:

1.Impact on Human:

  • Loss of life & physical injury
  • Increased stress; psychological trauma

2.Disease outbreak:

  • Contamination of water supplies leading to diseases
  • Rise in mosquito borne diseases

3.Impact on Economy:

  • Damage to buildings, roads and other infrastructures
  • Disruptions to industrial production
  • Disruptions to utility supplies
  • Impact on heritage or archaeological site
  • Post-disaster rescue and rehabilitation adds to financial burden of the government

4.Impact on Transport and Communication:

  • Increased traffic congestion, disruption in rail services
  • Disruption in communication- on telephone, internet cables

5.Impact on environment:

  • Loss of tree cover, loss of habitat
  • Impact on animals in zoo, stray animals

Notable Urban Flooding Events in India since 2000:

  • Hyderabad in 2000
  • Ahmadabad in 2001
  • Delhi in 2002 and 2003, 2009, 2010
  • Chennai in 2004, 2015
  • Mumbai in 2005, 2017
  • Surat in 2006
  • Kolkata in 2007
  • Jamshedpur in 2008
  • Guwahati in 2010
  • Bengaluru in 2017

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