Unscientific urbanization leading to Urban floods

Natural factors
  • Increasing downpour:
    • Southwest monsoon rainfall across the country from June 1 to July 13, 2020 was 12 per cent more than normal for this time, according to the India Meteorological Department (IMD).
    • The southwest monsoon distribution, however, has not been uniform across all regions.
    • Several states in the north, central and southern India have received excess rainfall. Andhra Pradesh received the highest — 61 per cent more than normal — followed by Bihar with an excess rainfall of 57 per cent.
    • Delhi received around 70 millimeters of rain July 19, 2020, the most in the past five years, according to reports.
  • Cyclonic storms and thunderstorms
  • occurrence of high tides impeding the drainage in coastal cities
Anthropogenic factors
  • Concretization:
    • Most cities had water bodies — lakes, ponds, streams, rivulets — which served three purposes: They replenished groundwater, catered to the city’s water needs and channelized excess rainfall to larger water bodies. Most such aquifers have fallen prey to concrete.
    • In Delhi, for example, a stream used to feed the Yamuna at about the place where the busy ITO today stands. It’s not without reason that the area is one of the most water-logged when it rains heavily in Delhi.
  • Wiping out of the wetlands:
    • Natural streams and watercourses have formed over thousands of years due to the forces of flowing water in the respective watersheds.
    • The encroaching of lakes in the cities by filling with mud and construction waste to recover the land leaves no place for water to get collected.g. Bengaluru had more than 250 lakes in the 1960s. There are scarcely 10 such water-bodies in a healthy state in the city today.
    • Chennai’s flood sink on its southern outskirts — the Pallikarnai marsh — was around 5,000 hectares in the 1950s. After the horrific floods in November last year, it was found that it had shrunk to 600 hectares.
    • The rivers, Cooum and Adyar, and the Buckingham Canal in Chennai have become dumping grounds. So have Mumbai’s wetlands near Sewri and other areas in New Mumbai. In fact, the city became alive to the river it has lost to real estate — the Mithi — after the terrible floods of 2005.
  • Poor Water and Sewerage Management:
    • With most cities lacking proper sewerage facilities, people dispose sewage in stormwater drains. The problem becomes worse when industries discharge their polluted water into such drains.
    • All this compromises the capacities of stormwater drains and also results in polluted water flowing into the larger water bodies.
    • Storm water drainage systems in the past were designed for rainfall intensity of 12 – 20 mm.
    • These capacities have been getting very easily overwhelmed whenever rainfall of higher intensity has been experienced.
    • Further, the systems very often do not work to the designed capacities because of very poor maintenance.
    • Stormwater drains cannot take the burden of the water that once used to seep into the ground.
    • Moreover, cities do not make the distinction between Stormwater drains and sewage disposal outlets.
  • Encroachment and Illegal constructions:
    • Encroachments are also a major problem in many cities and towns.
    • Real estate activity blocks the path of water; the city roads get waterlogged.
    • there have been large scale encroachments on the natural drains and the river flood plains.
    • Consequently, the capacity of the natural drains has decreased, resulting in flooding.
    • Improper disposal of solid waste, including domestic, commercial and industrial waste and dumping of construction debris into the drains also contributes significantly to reducing their capacities.
  • Deforestation:
    • Large areas of forests near the rivers/catchment of cities are used to make room for settlements, roads and farm lands and is being cleared due to which soil is quickly lost to drains.
    • This raises the drain-bed causing over flow and in turn urban flooding.
Administrative factors
  • Lack of flood control measures:
    • The growth in concretization of land has increased surface run-off due to near lack of percolation of water into underground aquifers. This coupled with no strict laws with respect to rain water recharge facilities an ideal flooding situation.
  • Multiple authorities in a city but owning responsibility by none:
    • The real estate mafia and corruption in local revenue offices are a deadly combination for converting wetlands into concrete structures. This reduces the area of lakes and may even vanish lakes out of official records.
    • Lack of sufficient financial resources with the urban local bodies.

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