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Wednesday, October 20, 2021

Lessons Mumbai didn’t learn

July 2005 deluge was followed by much planning, Tuesday shows city still cannot deal with heavy rain. Dozens of de-watering pumps for localised relief also suffered technical glitches, as conceded by the municipal commissioner.

Written by Kavitha Iyer |
Updated: August 31, 2017 8:35:12 am
mumbai rains, mumbai, Mumbai rainfall, Mumbai waterlogging, Mumbai weather, Mumbai floods, mumbai heavy rain,mumbai monsoon, mumbai drains, mumbai river, mumbai news, In Borivili, after the Dahisar river overflowed into the streets. At least 11 cars were washed away into the river; countless others are still upside down. (Amit Chakravarty)

Tuesday’s rainfall was only one-third of the rainfall that caused the deluge of July 26, 2005. Yet flood waters did not recede hours after the rain stopped, just like in 2005. And the reasons remain much the same.

The old lot of Mumbai’s municipal engineers often said that the giant underground drain or sewer in which a murderous Amitabh Bachchan is chased and fatally shot by his police inspector son, also Bachchan, was inspired by real South Mumbai drains, wide enough to accommodate several gun-toting men, framed by masonry walls. That was colonial engineering dating back to 1860-1900, some of it continuing to serve Mumbai’s flood waters, but limited to South Mumbai.

The suburbs, where the bulk of Mumbai’s millions live, are served mostly by roadside drains and the nullah system, open drains in which hundreds of tonnes of garbage are chucked each year by citizens, to be removed in an ever-inadequate pre-monsoon ‘desilting’ exercise. Much of these nullah networks also have long routes, flowing several kilometres through congested localities before discharging into the sea, often through outfalls located below mean sea level. This simply means tidal flow rushes into the city, and if it’s raining heavily when the tide is sufficiently high, then drainage is impossible.

But Tuesday’s highest tide had subsided by evening, and flood waters in many places — railway tracks, areas near the Mithi and Dahisar rivers, near large nullah systems —did not recede even past midnight. Notwithstanding the BMC’s and Railways’ claims, this is evidence of inadequately de-clogged drains. Dozens of de-watering pumps for localised relief also suffered technical glitches, as conceded by the municipal commissioner.

Planned, unplanned

Planners with a long-term view have also said part of 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 (Mumbai’s flood waters are among the dirtiest).

While Mumbai’s drains had an average capacity of 25 mm of rain every hour, the system was augmented to tackle 50 mm of rain per hour — in theory at least. And yet experts, including members of a fact-finding committee set up after the July 2005 deluge, have conceded that at least major roads and traffic junctions should have drainage systems capable to tackle floods with a once-in-100-years probability.

In the aftermath of the 944-mm deluge, the state and civic agencies undertook a series of projects, key among them being the decision to finally implement the Brimstowad (Brihanmumbai Storm Water Drainage) project, whose cost had more grown manifold since being proposed in the 1990s. Resources were spent on measures such as standard operation protocol for disaster management units, better-equipped disaster cells and control rooms, better forecasting systems, etc.

Yet, incredibly for a city by the sea, a range of long-term measures, accepted in principle, were never undertaken or were left incomplete. Recommendations to protect the Sanjay Gandhi National Park within the city limits, construct detention basins for flood water, demarcate flood-prone zones on Development Plan sheets, were never undertaken. An initiative to prepare contour maps for a flood modelling system remains incomplete — civic officials confirm that contour maps for drains were prepared, not for the rest of the city. (This means in heavy rain, municipal engineers know which drains’ contours will allow for retention of water longer, but no scientific information exists, for example, on which direction the Mithi river’s flood waters will rush out). Other recommendations to empower the Maharashtra Pollution Control Board to ensure compliance of environmental regulations by municipalities, a Mumbai Watershed Council to advise all agencies on planning for days like Tuesday, etc were never undertaken.

mumbai rains, mumbai, Mumbai rainfall, Mumbai waterlogging, Mumbai weather, Mumbai floods, mumbai heavy rain,mumbai monsoon, mumbai drains, mumbai river, mumbai news, Commutters stranded at Hindamatha, Parel as heavy rains lash on Mumbai city on tuesday.
(Express photo by Ganesh Shirsekar)

The rivers

River floods are different from floods caused by undue, sudden pressure on local drainage networks. By Tuesday evening, it emerged that the Dahisar and Mithi rivers were in spate. The arterial Western Express Highway and Lal Bahadur Shastri Marg were both inundated partially because of the overflowing rivers. Mumbai and its immediate suburbs are home to at least four separate river systems. The Mithi runs nearly 18 km, the Dahisar about 12 km, Poisar and Oshiwara nearly 7 km each. Each of these is now little more than a mother drain for suburban nullah networks, extensive encroachments reducing their width to barely a couple of metres in some places.

In fact, one of the key recommendations of an extensive report submitted by a fact-finding committee after the 2005 deluge was to restore degraded rivers and river-banks, to probe pollution and encroachment problems for each river, identify specific boundaries for each river, establish buffer zones, etc.

In reality, a grand plan for the rejuvenation of the Mithi, responsible for the worst destruction in the 2005 deluge, has been abandoned midway. A holistic revival of the river systems and early warning systems for those living along their banks have been long ignored alongside other related recommendations on reviving or upgrading hill slopes, lakes and ponds.


Casualties were fewer than in July 2005, and it was apparent Tuesday that the state’s response has come a long way since then.

The depth and reach of social media have made Twitter, Facebook and WhatsApp critical tools for dissemination of advisories and real-time situation updates. Mumbai’s Doppler radar-based weather forecasting system was recommended after the 2005 deluge, and installed. Various agencies, connected via hotline after 2005, coordinated effectively.

But advisories to stay indoors came too late, only after the trains had slowed due to submerged tracks and after the first visuals of cars and people stuck in knee-high waters emerged. Also, the CCTV camera network, installed after the Mumbai terror attack, can now monitor areas of traffic congestion and rising floods. It’s unclear yet how well or how early on Tuesday this infrastructure was used to manage the traffic chaos.

Early warning advisory systems the world over are built on the understanding that lead time available for gauging the intensity of an impending disaster and disseminating information is a very small window. For Mumbai, flood warnings based on the intensity of rain in any 15-minute duration are easy to build. The tougher challenge will be drafting detailed but precise advisories that are accurate, localised, accessible to everybody including the millions not on Twitter and disseminated in a well-practised drill.


assam floods, assam, floods, northeast floods, assam flood, assam weather, Sarbananda sonowal, bihar floods, floods in india, assam flood update, assam floods death toll, indian express news Flood affected villagers move in a boat in search of higher lands in Pokoria village, east of Gauhati, north eastern Assam state, India, Monday, Aug. 14, 2017. Heavy monsoon rains have unleashed landslides and floods that killed dozens of people in recent days and displaced millions more across northern India, southern Nepal and Bangladesh. (AP Photo/Anupam Nath)


1141 mm, 157 dead

Over 55 lakh affected in 3 successive waves, crops lost over nearly 4 lakh hectares, nearly 30,000 houses damages. Prime Minister Narendra Modi announced a Rs 2,000-crore package for various flood-mitigation measures in the Northeast. Among other states, Mizoram has received 2,553 mm, Meghalaya 2,109 mm, Arunachal 1,386 mm (48 deaths), Tripura 1,554 mm (6 deaths), Nagaland 1,091 mm (19 deaths) and Manipur 596 mm (22 deaths)


806 mm, 514 dead

Crops over 63.67 hectares damaged, over 1.71 crore people affected, 293 animals dead. The Prime Minister has announced Rs 500 crore for the state.


723 mm, 247 dead

Crops worth Rs 867 crore damaged over 10.98 lakh hectares, 6.44 lakh farmers affected. Rs 500 crore announced by PM Modi.

Uttar Pradesh

493 mm, 103 dead

Nearly 27 lakh affected, crop loss estimated at over Rs 98 crore

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