india

Updated: Oct 14, 2019 07:08 IST

Every day, Mumbai dumps 80 – 110 metric tons (MT) of plastic waste into drains and water channels, an application submitted by environment group Vanashakti before the National Green Tribunal (NGT) in December 2018 said.

The application highlights the Maharashtra government’s failure to install nets across storm water drains in Mumbai to collect waste from nullahs before they empty out into creeks, rivers or the sea. The Maharashtra Pollution Control Board (MPCB), in a follow-up affidavit, said creeks, rivers and the sea along Mumbai’s 437.71sqkm coastal stretch is under threat with plastic waste as a major source among municipal solid waste.

“Plastic directly enters into nullahs by the general public and slums areas. Discharge of untreated domestic waste accounts for 93% of the source of pollution for these water bodies,” read MPCB’s affidavit.

Applicants said the quantum of plastic entering drains and water channels in 2019 is much more if not the same. “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 water courses,” said Stalin D, director, Vanashakti.

The cost of this carelessness hit home during the deluge on July 26, 2005, when Mumbai was pounded with 944mm rain in one day that claimed more than 1,000 lives.

Experts said the 2005 floods were as much a result of clogged open surface drains with solid waste including plastic, storm water 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.

Experts said flood peaks in urban areas are about two-eight times and flood volume is about six times when compared with the rural floods. “No city is safe from flood disasters,” said Kapil Gupta, professor, water resources engineering, department of civil engineering, Indian Institute of Technology – Bombay. “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 analysis by the Mumbai-based Veermata Jijabai Technological Institute (VJTI) spanning 45 years showed that changing rainfall patterns, extensive concretisation, open drains along roads choked with plastic and other waste together with more-than-a-century-old storm water drain system has led to an increase in the quantum of rain water turning into run-off, thereby causing frequent inundation in Mumbai. The team found that the city’s existing storm water drain system – it can handle only 25mm rain per hour – is unable to carry the increase in rain water 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, VJTI said of the total 186 outfalls in Mumbai, 135 are above mean sea level but below the high tide level, 46 outfalls below mean sea level, and 2,000km roadside open drain system that are mostly clogged with plastic and waste. Only 6 outfalls are above high tide level. “Flash floods and high tides therefore cause most of the outfalls to submerge under the sea water leaving it useless for disposal of city water,” he said.

Of the 186 outfalls, there are

85 major outfalls in city which drain sewage mixed with plastic to Arabian Sea directly, eight at Mahim creek and 12 at Mahul creek.

There are 29 outfalls in western suburbs draining directly into sea while 14 drain into Mithi river which ultimately joins Mahim creek. In eastern suburbs, 14 outfalls discharge in Thane creek while six discharge in Mahul creek and 8 into Mahim creek. VH Khandkar, former chief engineer, storm water drains (SWD) department of the Brihnamumbai Municipal Corporation (BMC) had installed trash booms (like nets with thin meshes installed at the mouth of creeks to stop solid waste) across.