Bombay Natural History Society (BNHS) has commenced a biodiversity monitoring survey at Sanjay Gandhi National Park (SGNP) along the route of a proposed subterranean tunnel, which will connect Borivli to Thane and reduce travel time between Mumbai’s eastern and western suburbs from one hour to around 15 minutes. The twin tunnels will traverse the boundary of the SGNP protected area for 4.7kms, connecting Film City in Goregaon to Amar Nagar in Mulund.

BNHS’s first quarterly report, as part of its three-year-long exercise, is due within a couple of months, officials privy to the development said. The Brihanmumbai Municipal Corporation (BMC) is footing 4 crore for this, which officials likened to a similar monitoring and mitigation study for avian biodiversity being carried out in Thane Creek by BNHS as a result of the trans-harbour link project.

BNHS had been engaged as a consultant for the SGNP twin-tunnel project at the behest of the National Board for Wildlife at the time of granting wildlife clearance for the project in 2019. The ongoing biodiversity study, according to a forest department official, will first make a thorough inventory of all flora and fauna found within the study area prior to the beginning of construction in March 2022.

“The tunnel line itself is around 50 metres wide and the study area extends to 500 metres on each side of the tunnel line. From plants to insects, spiders, reptiles, and larger mammals like leopards and deer, all will be accounted for. The study has been underway for two months and the study area has been divided into different grids. BNHS has formed a dedicated team which spends 10 days of every month in the field, surveying these grids,” said the official.

Once inventory is completed, researchers will attempt to identify those species which may face a higher risk as a result of the tunnelling work. A preliminary ecological sensitivity report submitted to the forest department by Maharashtra State Road Development Corporation (MSRDC) suggests that leopard, sambar deer, Indian python, Indian cobra and Russell’s vipers “are the major wildlife found in some of the study areas around the proposed alignment”.

The preliminary report had also identified a few species of “conservation importance”, including three species of plants — saraca ashoka (Sita ashok), garcinia indica (Kokam), White Orchids; three mammals — leopard, rusty spotted cat and sambar deer; two birds — brown fish owl, mottled wood owl; as well as the Atlas moth and blue mormon butterfly which are the largest known butterfly and moth species.

In all, the forest patches and protected areas around SGNP provide a habitat for over 1,000 plant species; around 251 species of migratory, land and water birds; 50,000 species of insects; 43 species of mammals; 38 species of reptiles; nine species of amphibians; 150 species of butterflies; and a large variety of fish.

“The main impact is expected from vibrations caused due to tunnelling during construction phase. BNHS’s contract with BMC states that they will continue to monitor the area for a period of two years from the date of construction. So, if there is any cause for worry, it will be reported to us and appropriate steps for conservation will be taken,” said the forest department official.

A technical pre-feasibility report for the proposed tunnel by MSRDC in November 2017 had noted that “project activities such as drilling would temporarily produce activity and manual entrance that would disturb wildlife and cause them to disperse. This local displacement would create a short-term impact to large and small mammals. Displacement would affect a small number of overwintering breeding birds. Overall, effects on wildlife would be short-term and minor.”

The proposed tunnel has recently become a topic of discussion again among city’s green campaigners who questioned the lack of a dedicated environment impact assessment (EIA) for the project, and its exemption from environmental clearance (EC) despite being located within the boundary of a protected area.

Stalin D, director of NGO Vanashakti, said the tunnel could potentially destroy the underlying aquifers feeding Tulsi and Vihar lakes, which provide Mumbai with a modicum of water. He also stressed that the cumulative impact of all projects encroaching upon the national park — such as the dedicated freight corridor which includes 10.8 hectares of forestland diversion in SGNP — be considered as opposed to assessments of individual infra works.

Veteran environmentalist Sunjoy Monga, however, said that the benefits of the project, in terms of reducing traffic congestion and air pollution in the city, outweigh any ecological risk. “The sheer density of cars per square kilometre of road in Mumbai is among the highest in the world. Tunnelling technologies are fairly sophisticated at this stage and have been used for similar projects by more developed nations. Exemption from EIA is another matter, but speaking specifically of this project, it is an important one that will have environmental benefits,” he said.

G Mallikarjuna, chief conservator of forests, SGNP, could not be reached despite several attempts.

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