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Thursday, May 26, 2022

140-year-old drainage system, highest rain since ‘74 — why south Mumbai flooded

The amount of rain that Mumbai experiences has remained unchanged over the last 80 years. The old drainage system, along with Mumbai’s then abundant open spaces, allowed the percolation of water and its faster dispersal.

Written by Laxman Singh | Mumbai |
Updated: August 7, 2020 1:47:33 pm
mumbai floods, Mumbai rains, mumbai monsoon, mumbai water logging, mumbai flooding, mumbai drainage system, mumbai city news A waterlogged road in Chembur on Thursday. (Photo by Pradip Das)

A combined paper prepared by more than two dozen experts in The Journal of Climate Change published in 2011 had stated that by upgrading the drainage system in Mumbai, losses associated with a one-in-100-year flood event could be reduced by 70 per cent.

On Wednesday, large parts of south Mumbai were inundated after the island city reported its heaviest single-day downpour in August in 46 years with 293.8 mm of rainfall.

“The island city’s drainage system is 140 years old, designed by the British. At that time, most of the island city was green. The drainage system was designed considering that 50 per cent of rainwater will be going through drains and the rest will percolate into the ground water. Now very few parts in south Mumbai are open but the underground drainage system has remained the same,” environmentalist Debi Goenka said.

The amount of rain that Mumbai experiences has remained unchanged over the last 80 years. The old drainage system, along with Mumbai’s then abundant open spaces, allowed the percolation of water and its faster dispersal. The gradual concretisation of open spaces has meant that the percolation of water does not happen the way it used to be.

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On Wednesday, many areas in south Mumbai, which usually do not see waterlogging, were flooded for hours. According to the India Meteorological Department, in nine hours, its Colaba observatory recorded 225 mm of rainfall. The last time the area had seen heavier rain than Wednesday’s was in 1974.

Areas like Churchgate, Marine Drive, Fort, Girgaum, Khetwadi, Walkeshwar Road, J J Marg, Gol Deol, Bhendi Bazaar, Kalbadevi were flooded and water entered several houses.

Urban planner and executive director of Urban Design Research Institute (UDRI), Pankaj Joshi, said that the city needs to change its planning in view of climate change. “Some are still denying climate change. This phenomenon of heavy rains in a few hours is happening frequently. Our storm water drain network can drain out 25 mm to 50 mm per hour but draining 280 mm is virtually impossible. You need to be prepared and to quickly understand that our city needs to be engineered. Now, we should look for preventing disaster rather than management,”said Joshi.

He pointed out that BMC’s BRIMSTOWAD (Brihanmumbai Storm Water Drain System) project has been going on for 13 years. It comprised 58 works, including rehabilitation and augmentation of underground drains, widening and deepening of nullahs and construction of pumping stations. After spending Rs 1,200 crore so far, the civic body has only completed 38 works.

According to BMC data, the island city has the highest population density with around 46,000 people living in 1 sq km as against the city’s average of 29,000 in per sq km. The island city is spread over 68.71 sq km with a population of 31.58 lakh and being the oldest part of the city, has hardly any place to develop further.

Environmental activists, however, pointed out that the construction of the coastal road as well as the Metro, which have been going on for the last few years, have accelerated south Mumbai’s urban infrastructure woes.

“The problem is accentuated because of the combination of reclamation and construction. During such projects, the barriers set up, construction materials and debris may clog the drainage system. The more hard-paved barriers you create, the more water tends to run off. Some of these situations are unavoidable but then you should have the right drainage channel to reduce waterlogging,” said Hussain Indorewala, professor in Kamala Raheja Vidyanidhi Institute of Architecture in Mumbai.

In the past, BMC has sent written to the Mumbai Metro Rail Corporation Limited on Metro 3 (Colaba-Seepz) work clogging and damaging drains.

The BMC, meanwhile, believes that what happened on Wednesday was a weather anomaly and the flooding was the result of heavy rains that the area experienced in a short period of time.

“Coastal road project contractors have taken all precautions for discharge of drain water. At one place near Nair hospital, there was some clogging of drains due to their work but that has also been cleared by them. Heavy rainfall in a very short time is the reason behind flooding in these areas,” said an official from BMC’s storm water drainage department.

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