Vehicles move through waterlogged streets during heavy monsoon rain, in Mumbai, on 1 July, 2019 | Photo: Mitesh Bhuvad | PTI
Vehicles move through waterlogged streets during heavy monsoon rain, in Mumbai, on 1 July, 2019 | Photo: Mitesh Bhuvad | PTI
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Mumbai: Heavy rain lashed Mumbai between Monday and Tuesday, killing at least 18 people and disrupting rail and air traffic. In the 24 hours from 8 am Monday to 8 am Tuesday, the Santacruz weather station, representative of Mumbai suburbs, recorded 375.2 mm of rain, which, according to the Indian Meteorological Department (IMD), is the highest July rain on a single day the city has received in a decade.

This is exceptionally heavy rain for any city, even by the IMD’s terminology, which classifies rainfall between 124.5 mm and 244.4 mm as “heavy” and anything beyond as being “exceptional”.

The Colaba weather station, representative of the Mumbai island city, recorded 137.8 mm rain in the same 24-hour period, which qualifies as “very heavy rain”.

This is also the second highest rainfall on a July day in Mumbai since 1974 — the first being 26 July 2005, when Mumbai witnessed one of its worst floods. Tuesday’s rain was nowhere close to the 944 mm that pelted the city then but the effect was still devastating.

By Tuesday morning, there were reports of at least 18 people being dead when a wall collapsed at about 2 am in the intervening night of Monday and Tuesday at Malad, a far-western Mumbai suburb. Several others were injured and rushed to the hospital.

In another incident at Kalyan, a satellite town in the larger Mumbai Metropolitan Region, three died and at least one more was injured when a school compound wall collapsed on an adjoining chawl (slum). Several parts of Mumbai were water-logged. Commuters were stuck in trains and at railway platforms till the wee hours of Tuesday morning, and railway and airport services were disrupted.

While there have been minor improvements since the July 2005 day that holds the record for the highest 24-hour July rain in four decades, there are lessons that Mumbai is yet to learn.

Storm-water drains

Mumbai is serviced by age-old drains — 525 km of underground drains and laterals in the island city, most of which date back to British rule. There is about 2,000 km of roadside surface drains, mainly in the suburbs.

These are further connected by major and minor nallahs, or open drains, from which civic officials try to weed out trash in the annual pre-monsoon de-silting exercise, often criticised for being inadequate and shoddy.

In heavy rain, it is these arteries of the city, designed to handle a measly 25 mm of rain per hour, that get clogged, spewing water onto the road.

Yet, the ambitious BRIMSTOWAD project, meant to augment the drainage capacity to 50 mm, setting up of pumping stations, automatic rain gauges, and widening and deepening existing nallahs and so on, is still incomplete despite first being conceived in 1993, and being seriously taken up for implementation after the 2005 deluge.

According to the Brihanmumbai Municipal Corporation’s (BMC’s) flood preparedness guidelines for 2019, the civic body has been able to complete only 16 out of the 20 works identified in the first phase of the project and 11 out of the 38 works earmarked for the second phase.

Twenty-eight works across the two phases are still underway, while tenders are yet to be invited for three more works. So far, the civic body has poured in a little over Rs 2,000 crore on the project.

“Rehabilitation of slum dwellers living along the nallahs and procuring land for the pumping stations have been some of the major reasons for the delay,” a BMC official said.

Also read: Talk Point: Why is flooding in Mumbai an annual feature & what’s the solution to it?

Water bodies

On Tuesday, the Mithi River, which has the largest catchment area and is a source of natural drainage for the suburbs, was overflowing again. The angry swell of the river, which had been reduced to nearly a sewer, was one of the key reasons for the July 2005 inundation.

One of the takeaways from 2005 was the urgent need to improve the carrying capacity of the 17.8-km river through widening and deepening it. While the water body is now definitely several notches better than what it was in 2005 at several locations, the civic body has still not fully completed the rejuvenation exercise.

According to the BMC, it has completed 95 per cent of the widening and deepening of the river. However, there are still encroachments and small industrial units along the river bank, making it susceptible to the constant discharge of pollutants and garbage.

There is, however, at least better awareness of the perils of the abused river hitting back, as the BMC’s disaster management cell evacuated about 1,000 people living along the Mithi in North Central Mumbai this time around.

The city’s other water bodies — the Dahisar, Poisar and Oshiwara rivers — are in no better shape. There have been plans of training, cleaning and beautifying the rivers but removing politically-protected encroachments along the banks remains a major hurdle.

Best practices

As the rains made national headlines Monday, BMC Commissioner Pravin Pardeshi told India Today that over the past 50 years the extent of built-up area in Mumbai has impacted the city’s water run-off coefficient, which in normal cases is 0.4 to 0.6.

A run-off coefficient of 0.4 means if there is 100 mm rainfall, 40 mm will move to the drains while the rest will percolate into the ground.

“But, if you have built-up 100 per cent of the area then all 100 mm will move to the storm-water drains and our drains have the capacity to handle only a 60 per cent run-off so there is an additional amount of rain that storm-water drains can’t take care of,” he added. “This combined with high tide, when water cannot be discharged in the sea, leads to waterlogging.”

This is the crux of the problem, but despite acknowledging it, there is little conscious effort in creating open spaces, holding ponds and limit concretisation to improve the city’s run-off co-efficient.

Experts over the years have suggested measures based on best international practices, such as having drains at chronic spots with an extraordinary capacity to handle 100 mm per hour or have deep tunnelling to store flood water underground till it can be pumped out when the tide is low.

Such international best practices are, however, still a dream with the city struggling with basic planning deficiencies.

“We are struggling to complete drainage projects planned more than a decade ago,” Sulakshana Mahajan, an urban planner said. “We still don’t have either transparent topographical maps and flood contour maps or the mindset to use such technology for better governance.”

“These are basic deficiencies,” she added.

Also read: There’s a big change coming to how India uses funds after cyclones, earthquakes, floods


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