Explained: What caused weekend flooding outside Mumbai; what can be done?https://indianexpress.com/article/explained/mumbai-rains-maharashtra-flooding-flooding-5859105/

Explained: What caused weekend flooding outside Mumbai; what can be done?

The MMR, which sprawls over more than 10 times the geographical area of Mumbai, is dotted by semi-rural areas and municipalities that sometimes serve as dormitory townships for India’s financial capital.

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Flooding in Kalyan.

The eastern part of the Mumbai Metropolitan Region (MMR) was inundated over the weekend after the townships of Kalyan, Ulhasnagar, Murbad and Ambernath all received around 300 mm rain in the 24 hours ending 8 am on July 27. Almost exactly a year earlier, the twin satellite towns of Vasai-Virar had been all but cut off from Mumbai for two days as floods snapped rail and road links.

The MMR, which sprawls over more than 10 times the geographical area of Mumbai, is dotted by semi-rural areas and municipalities that sometimes serve as dormitory townships for India’s financial capital. What makes this coastal urban agglomeration prone to flooding of the kind seen in Thane district over Friday and Saturday?

Reckless construction

Many of Mumbai’s satellite towns are located along the Kalu, Ulhas, Waldhuni, and Bhatsa rivers that shimmy down the MMR, passing through thickly populated areas including Ulhasnagar, Titwala, Badlapur, Vithalwadi, and Ambernath. All these areas have seen a massive spurt in construction activity over the past two to three decades — and almost all these rivers have the problems that come with unplanned urbanisation: encroachments, illegal sand dredging, dumping of effluents, and construction activity on their floodplains.

A March 2015 study prepared for the Mumbai Metropolitan Region Development Authority (MMRDA) reported that forest cover in the MMR had fallen from about a third of the total area in 1987 to 21% in 2015. Wastelands, floodplains, mangrove areas, all have seen construction activity. Saturday’s overhead images from Naval choppers showed the Mahalaxmi Express marooned in what seems to be the floodplains of the Ulhas river. Railway officials say the line was originally a good distance away from the river’s buffer areas, but unplanned construction along both banks has rendered the tracks vulnerable to submergence when the river is in spate, with the city’s drains emptying into the railway areas simultaneously.

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Worst-affected rivers

The Mithi in spate caused much of the havoc on July 26, 2005, when a cloudburst dumped 944 mm of rain on Mumbai within a span of 24 hours; the overflowing Ulhas is likely to be blamed for parts of Ulhasnagar going under on Friday evening and Saturday.

Picnickers at a resort on its banks had to be rescued. The river passes through Badlapur and Vangani, where the dramatic rescue of train passengers took place.

The winding Ulhas flows 120-plus km from its source in the Sahyadris to the Arabian Sea via Vasai creek, passing the picturesque Karat and Neral regions, and receiving waters from as far as the Palasdhari dam, the Poshir river, Chikoli dam, Barvi dam, before merging with the confluence of the Bhatsa and Kalu rivers. Multiple areas along its banks — Shahad, Ambivali, Dombivali, Kongaon, Mothagaon, Ambernath, Ulhasnagar and Badlapur — were affected on Friday and Saturday.

The Kalu river’s overflowing waters caused some parts of Titwala to be flooded, while the much less urbanised Vasind-Asangaon area were inundated by overflow from the Bhatsa river.

What can be done?

Will cleaning up these rivers reduce the likelihood of floods?

There are over 20 reservoirs/dams within the municipal limits of urban local bodies in the MMR. Modaksagar and Tansa, which serve Mumbai, were already overflowing. Villages on the banks of the Vaitarna river had been issued their annual warning over a week back. On Sunday, one floodgate of the Middle Vaitarna Dam, located further north on the Vaitarna river, was opened.

But downstream villages along the banks of these rivers are no longer alone in danger of inundation. As natural adaptation and flood resilient geography is broken down by unplanned construction activity. Holding ponds, mangroves, wetlands, salt pan lands, and other buffers have disappeared. Much of the devastation in Vasai-Virar on the two days of flooding in July 2018 was linked to the choking of the creek areas, and at least some of the latest flood-related damage will be found connected to the upstream damage to the rivers’ ecology.

The 13 west-flowing rivers and their 21 tributaries are important natural floodwater drainage systems for the region. At a wider level, the problem of where the MMR gets its drinking water also comes into play — multiple dams on these rivers are in various stages of construction or planning, including the Kalu, Shai, Gargai, Pinjal, Poshir and Barvi dams. The unplanned densification of townships downstream of these dams makes the responsibilities of these municipalities that much more grave.

The population of the ‘Rest of MMR’, excluding Mumbai, has grown from 18 lakh in 1971 to 106 lakh according to the 2011 Census, a number that does not account for more recent additions of peri-urban areas into the MMR. Decadal growth rate of population for parts of the MMR excluding Mumbai was found to be nearly 55 per cent. There are also large industrial belts in the MMR — those across the TTC (Trans-Thane Creek) area, Taloja, Waghle Estate, Dombivali, Ambernath, Bhiwandi, etc.

An overhaul of municipal amenities in these regions, planned in a holistic way that takes into account sustainable water needs, sustainable water supply solutions, likely floodwaters from new reservoirs and dams in the region, maintaining buffer zones that are no-go areas for construction, will be the minimum requirement for flood-proofing this region.