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Mumbai plans to build 4 sea walls: Can they keep the water at bay?

The Maharashtra coastal zone authority, MCZMA, is planning to build 20 anti-sea erosion bunds along the Konkan coast, including nine at Ratnagiri, five at Raigad, and one each in Thane and Sindhudurg districts.

mumbai Updated: Aug 25, 2018 12:31 IST
Badri Chatterjee
Badri Chatterjee
Hindustan Times, Mumbai
Mumbai sea wall,Mumbai news,Sea walls
High tide at Worli Sea Face in Mumbai.(Anshuman Poyrekar/HT Photo)

As rising sea levels threaten to inundate as much as 40% of Mumbai’s urban sprawl within the next century, the Maharashtra Coastal Zone Management Authority (MCZMA) has decided to build four bunds or sea walls at four spots along the city’s shorelines — two in Colaba (at Geeta Colony and near Bombay Presidency Radio Club), one at Shivaji Park, Dadar and one near Haji Ali.

Overall, MCZMA plans to build 20 anti-sea erosion bunds along the Konkan coast, including nine at Ratnagiri, five at Raigad, and one each in Thane (Retibunder) and Sindhudurg districts. HT had reported earlier this year that the state environment department had rejected 60% of seawall proposals and opted for softer measures such as tree plantations. However, considering the visible impacts of climate change and predicted sea level rise, the decision was taken, said the state environment department.

The proposal from the state’s public works department (PWD) was cleared by MCZMA during a meeting on Tuesday, and construction is expected to begin post monsoon. “These bunds can dissipate the energy of high-intensity waves. At the same time, it allows sand to sieve through,” said Anil Diggikar, principal secretary, state environment department. “The exact size and type of bunds will be decided but we usually go for tetrapods or large rocks (called membranes). The effects of climate change and effects of flooding recently witnessed in Kerala have all been taken into account while finalising the construction of these bunds.”

Heavy rains in July this year coupled with high tide saw waves as high as 4.96m (4.5m waves are identified as high tide) along the Mumbai coastline that dumped large tracts of garbage along Marine Drive in south Mumbai.

Maharashtra’s coastal authority will build four sea bunds in Mumbai — two in Colaba, one in Dadar and one near Haji Ali — to combat rising sea levels and coastal erosion
Mumbai could lose more than 25 sq km of its urban sprawl due to rise in sea levels over the next 100 years, according to a study done by Jawaharlal Nehru University. That’s the area equivalent of nearly 1,700 Wankhede Stadiums. The National Institute of Oceanography estimates that a 1.5m sea level rise could swallow 40% of the city’s land. Both studies cited global warming and temperature rise over the next century as causes.
The Maharashtra Shoreline Management Plan 2017 has identified the nature and level of risks to existing infrastructure across various coastal strips and has recommended the following actions
These satellite images set 17 years apart show how rising sea levelshave eroded nearly 18m of beach area in Mahim

A February 14 report by HT highlighted that sea erosion in Dadar, Malabar Hill, Mahim and Versova was posing a major risk to existing infrastructure, the Maharashtra Shoreline Management Plan 2017 had found. “After the witnessing the feasibility of these proposed bunds, more such barriers will be constructed in other areas that are falling prey to soil erosion,” said a senior PWD official.

Marine experts said the construction of these bunds could cause more harm. “The life of such bunds is not more than six years. When the sea is not allowed to take its natural course, it inundates other areas,” said E Vivekanandan, former principal scientist and national consultant, Central Marine Fisheries Research Institute. “Bunds will significantly affect fishing because they will make surface water behave erratically. In locations such as Velas and Anjarle in Ratnagiri where turtle nesting sites are located, such bunds come in the way of these marine species reaching the shoreline.”

The Maharashtra Maritime Board (MMB) said alternative solutions such as tree planting, beach nourishment, artificial reefs and sandbags are also being considered. “These are more ecofriendly solutions, and they are implemented after scientific studies at least 100 to 200m offshore,” said Jitendra Raisinghani, deputy director, coordination, MMB.

First Published: Aug 25, 2018 12:27 IST