Mumbai Floods – An analysis

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August 31, 2017

What is the issue?

Flooding seems to recur almost every year in Mumbai, with this year being particularly severe.

How does Mumbai’s drainage network look?

  • Massive underground sewers built during the colonial era dating back to 1860-1900 are impressive with some of it still in use, but is limited to South Mumbai.
  • The suburbs of Mumbai are served mostly by open drains, into which tonnes of garbage are dumped each year by citizens.
  • Pre-monsoon ‘desilting’ exercises are carried out every year, which has proved to be ever-inadequate. 
  • Much of these sewer networks flow several kilometres through congested localities before discharging into the sea, often through outfalls located below mean sea level.
  • This means if it’s raining heavily when the tide is sufficiently high, drainage is impossible.

How to deal with the Tides?

  • The problem is that Mumbai’s flood waters are simply discharged in the Arabian Sea through gravity.
  • There are international examples of balancing reservoirs and deep tunnel systems for underground storage of flood waters to be pumped out later when the tides are low.
  • Best practices also involve adopting and conserving rainwater within a catchment area itself, through local storage and recharging alongside filtration systems.

What is unusual about the current floods?

  • Although, the rainfall was only one-third of the rainfall that caused the 2005 deluge, flood water failed to recede and the reasons remain much the same.
  • Dozens of de-watering pumps for localised relief also suffered technical glitches, as conceded by the municipal commissioner.
  • While, even after the highest tide had subsided, flood waters in many places did not recede, which is clear validation of clogged drains.

What are the problems plaguing Mumbai’s drainage?

  • Insufficient Drains – Although the drainage capacity of the entire city isn’t impressive as such, experts have explicitly conceded that at least major roads and traffic junctions fall far short of the required. 
  • Brimstowad Project – After much delay this project got a go ahead, with resources being spent on measures such as standard operation protocol, better-equipped disaster cells and forecasting systems.
  • Yet, incredibly, a range of long-term measures, accepted in principle, were left incomplete.
  • Contour mapping - Although contour maps for drains were prepared it remains incomplete for the rest of the city.
  • This means, although the prediction of the drainage flow is possible, there is no data point to predict how a river’s flood waters will rush out.
  • Other Issues - Recommendations to protect the Sanjay Gandhi National Park within the city limits, construct detention basins for flood water, demarcate flood-prone zones were never undertaken
  • Also, recommendations to empower the Maharashtra Pollution Control Board to ensure compliance of environmental regulations by municipalities were never undertaken.

What is the impact of river overflows?

  • River floods are different from floods caused by undue, sudden pressure on local drainage networks.
  • Mumbai’s Context - Mumbai and its immediate suburbs are home to at least four separate river systems.
  • Extensive encroachments have reduced their width to barely a couple of metres in some places.
  • The arterial Western Express Highway and Lal Bahadur Shastri Marg were both inundated recently, partially because of the overflowing rivers.
  • Recommendations - One of the key recommendations of an extensive report submitted after the 2005 deluge was to restore degraded rivers and river-banks and to probe pollution.
  • The report also stressed on the encroachment problem, identifying specific boundaries for each river and establishing buffer zones.
  • Current Status - Sadly, a grand plan for the rejuvenation of the Mithi, has been abandoned midway.
  • A holistic revival of the river systems and early warning systems for has been long ignored.

How has the disaster response been?

  • The Positives - Casualties were fewer than in July 2005 and it was apparent that the state’s response has come a long way since then.
  • The hotline for connecting various agencies, introduced after 2005, proved critical.
  • Also, the depth and reach of social media for dissemination of advisories and real-time updates was found to be tremendous.
  • Areas Needing Betterment - Although ‘Doppler radar-based weather forecasting system’ was installed, advisories to stay indoors came too late.
  • Also, the CCTV camera network, which can monitor areas of traffic congestion and rising floods, seems to have been activated a little late.
  • Improvisation is needed for drafting detailed but precise advisories that are accurate, localised and accessible to everybody.


Source: IndianExpress

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