Oct 29, 2007

Mumbai Shoreline Erosion

Western India, 65 million years ago. Huge volcanic eruptions convulse the surface of the earth. Lava spews out of a longitudinal scar running all the way from Mumbai to Nagpur. As the ground cools, basalt formations like Malabar Hill and Gilbert Hill crystallize. A few hundred kilometres up north, the Western Ghats start to swell up. With the passage of time, a turbulent sea carves out more land and soon a string of islands are formed.

For those unsure about the long-term effects of coastal erosion on India’s commercial capital, visions of the post-Jurassic Age may hold the key to some answers. Scientists believe there was a time when not only were dinosaurs in this part of the world wiped out but large rocky outcrops jutting out from the mainland got severed and were left marooned in the Arabian Sea.

Mumbai’s geological history reveals a pattern of soil erosion, which explains the emergence of the seven islands and the presence of partly submerged isles like Butcher and Elephanta around it. A team from the National Institute of Oceanography (NIO) has recently helped reinforce this view by establishing a rate of sea level rise along the Arabian coast over the past century, thus suggesting an age-old decline in land mass. “The process taking place today is the key to the past,’’ says geologist and erstwhile Indian Institute of Technology (IIT) professor V Subramaniam, who has spent years studying physical features along the city’s coastline. Over the past three decades, Subramaniam has inspected beachfronts and bays running down from Cuffe Parade to Marve and found ample evidence of the terrain wearing away under constant buffeting by waves. “I have seen walls around buildings disappearing at Versova, you can imagine what is happening there,’’ he adds.

Down the ages, the shoreline is in fact believed to have evolved from a straight configuration into one indented by bays and creeks owing to such pressure. With tides going up to five metres and strong currents swirling close to land, the Mumbai coast is under active and constant attack. And the same activity, when extrapolated over millions of years under the influence of global warming and melting glaciers, leads scientists to believe there will be further ‘separation’ of portions from the mainland. “It may seem incredible, but Butcher Island and Elephanta were once part of the same land mass as Mumbai. To understand this phenomenon, you must look at terrain around Malabar Hill,’’ says Subramaniam.

The Hill, home to the city’s rich and famous, is a promontory that is lashed by waves on either side. Situated at the southern edge of a ridge that runs down through Cumballa Hill, parts of Worli and Pali Hill, it’s an area that lends itself to coastal disintegration. The early signs of stress along the shore near Raj Bhavan is visible to the expert’s eye; if unchecked, it could lead to corrosion and development of caves and small arches. Further on, as terrain crumbles and roofs collapse, the stage may be set for the strip to break away.

The question is, when? Conservative thinkers believe that given the rate at which the sea is rising, any such destruction can be slowed down or mitigated by constructing promenades and protective walls like the ones at Marine Drive or Carter Road. However, others fear there are changes coming which may be immediate. Debi Goenka, who’s at the forefront of Mumbai’s environmental movement, says new data shows “the Arctic ice caps are melting faster than thought to earlier’’ and this could have a profound impact on the behaviour of the sea.

Of course, doomsday predictions are leavened by oceanographers who are unwilling to rule out the possibility that coastal erosion along a stretch can reverse owing to shifts in wave fields and currents. A vanishing beach can have sand being deposited along it in the distant future. “I remember as a young boy how tiny Miramar beach used to be,’’ says a greying NIO director S R Shetye, whose institute overlooks the waterfront in Goa. “Today the same beach has widened in size and has sand constantly being deposited along it.’’