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Updated: Oct 14, 2019 00:12 IST

Mumbai: Mumbai’s creeks, rivers and 437.71 sq km coastal stretch are under threat because of the municipal solid waste with the bulk of it being plastic, the Maharashtra Pollution Control Board (MPCB) said in a follow-up affidavit to an application environment group Vanashakti submitted to the National Green Tribunal (NGT) in December 2018.

“Plastic directly enters into nullahs... Discharge of untreated domestic waste accounts for 93% of the source of pollution for these water bodies,” said the affidavit.

In its application, Vanashakti said that as many as 80-110 metric tonnes (MT) of plastic waste was being dumped into Mumbai’s drains and water channels daily, highlighting the government’s failure in installing nets to collect garbage before it flows into creeks, rivers, and the sea.

According to Vanashakti, the quantum of plastic entering drains and water channels in 2019 is much more. “The negligent attitude of Mumbaiites, especially those living near drains and creeks, has resulted in massive amounts of plastic waste, majority of which is single-use plastic, being dumped into the natural watercourses,” said Vanashakti director Stalin D.

The cost of this hit home during the deluge on July 26, 2005 in Mumbai that claimed over 1,000 lives.

Expert say that the 2005 floods were as much a result of clogged open surface drains with solid waste including plastic, stormwater drains and its channels as it was due to significant changes in land use across the city and illegal construction and encroachments along natural drains and the Mithi river.

Kapil Gupta, a water resources engineering professor at the Indian Institute of Technology Bombay, said that the city authorities should take measures to ensure that when heavy rainfall occurs, adequate drainage systems are in place and these are unclogged so that flooding does not occur in the vulnerable areas.

A recent Mumbai-based Veermata Jijabai Technological Institute (VJTI)’s analysis spanning 45 years showed that changing rainfall patterns, extensive concretisation, open drains along the roads choked with plastic and other waste together with more-than-a-century-old stormwater drain system has led to an increase in the quantum of rainwater turning into run-off, thereby causing frequent inundation in Mumbai.

It found that the city’s existing stormwater drain system, which can handle only 25mm rain per hour, is unable to carry the increase in rainwater discharge from 3,207 cubic meter per second in 1973 (cu.m/sec) to 4465cu.m/sec last year.

Darshan Sansare, principal investigator and research scholar at VJTI, said of the total 186 outfalls in Mumbai, 135 are above mean sea level but below the high tide level. He added 46 outfalls are below mean sea level, and 2,000 km roadside open drain system is mostly clogged with plastic and waste. Only 6 outfalls are above the high tide level. “Flash floods and high tides, therefore, cause most of the outfalls to submerge under the seawater leaving it useless for disposal of city water,” he said.

V H Khandkar, a former Brihnamumbai Municipal Corporation (BMC) chief engineer, said trash booms (nets with thin meshes installed at the mouth of creeks to stop solid waste) were installed across eight locations in Mumbai to address the plastic issue. “It was successful during the pre-monsoon period and a large amount of plastic waste was collected regularly from drains. However, when the load increased during monsoon, the booms could not contain the capacity. The plan was dropped,” he said.

An official, requesting anonymity, said based on NGT’s directives, a new plan using trash booms may be implemented post-monsoon to contain plastic waste from entering creeks.

The Maharashtra mangrove cell estimates that at least 50,000 MT of plastic waste is littered across mangrove forests in the Mumbai Metropolitan Region brought by creeks and other water channels to these salt-tolerant trees. “Mangroves, which have stilt roots, trap the trash. We have removed close to 18,000 MT over the past two years but the amount continues to come in every monsoon,” said N Vasudevan, additional principal chief conservator of forest, state mangrove cell.