Mumbai hopes tubes can protect coastline from encroaching seas

Darryl D'Monte Reuters AlertNet 11 Oct 10;

MUMBAI (AlertNet) - Around a third of the coastline north and south of Mumbai, India's financial capital and most populous city, is vulnerable to severe flooding from extreme weather and rising sea levels, according to a study that has yet to be published.

The number of people living in the Mumbai urban agglomeration will touch 28.5 million by 2020, making it the biggest city in the world, according to the Washington-based Population Institute.

As much as 14 percent of the 720 km (450 miles) coastline - with Mumbai roughly in the centre - is "highly" vulnerable, and 16 percent "moderately" vulnerable, according to the Hyderabad-based Indian National Centre for Ocean Services.

"The Indian ocean rim is predisposed to natural disasters," says the centre's T. Srinivasa Kumar. "A rise in the sea level due to a storm surge could lead to coastal flooding in a low-lying area or in an open creek or river mouth."

In July 2005, Mumbai, the capital of Maharashtra state, was hit by an unprecedented cloudburst - 944 mm in 10 hours - which shut down much of the city and took around 400 lives, besides causing millions of dollars of damage to property.

Just over half the population of Greater Mumbai, some 8 million people, live in slums, the highest proportion for any metropolis in the world. They have tended to squat along the coast and estuaries, leaving them exposed to hazards from flooding and sea level rise.

Mumbai residents know only too well that if torrential rain is accompanied by a high tide, the floodwater cannot escape and backs up into the city.

'NO MORE LAND TO MOVE TO'

Shirish Karlekar, a geographer from SP College in Pune, some 150 km (90 miles) inland from Mumbai, has been monitoring changes along the coast from just north of Mumbai to the southernmost tip of the state's coast for 20 years. In that period, the average sea level has risen by 5 to 6 cm.

On December 29 last year, the high tide rose by 4 cm near Ratnagiri town, which lies around 200 km (125 miles) south of Mumbai and is the home town of many Mumbai immigrants. Karlekar says the increase on the same day in 2008 was just 2 cm.

"In recent years, the sea level has risen at a much faster pace than in the early years of our study," he explains.

The ever-higher tides have led to salt water penetrating as much as a kilometre inland, damaging mangroves, eroding beaches and filling creeks with sand.

Sadanand Tandel recalls how the waves first entered his village of Deobagh (meaning God's garden) in coastal Sindhudurg district during the 1978 monsoon.

Since then, his village has lost 32 hectares (79 acres) of land, mainly valuable coconut groves.

"In the 1980s, the sea was more than 300 metres from my house and more than 1,000 casuarina (pine) trees were planted to protect the coast between my grove and the sea," Tandel said. Nonetheless, the sea threatens just 40 m from his doorstep today.

Tondawli village, 20 km (12 miles) to the north, has lost 40 hectares (100 acres), including some 500 coconut trees and space for drying fish.

Lakshmi Kochrekar, who tends a coconut plantation and isn't sure of her age, has had to rebuild her house twice due to the rising tides.

"I have no more land to move to now," she complains.

Village elders in this region say the sea's very behaviour is changing. Patterns of erosion and deposition are different.

While tides are eroding the coast more rapidly, debris is being deposited on an unprecedented scale in other areas.

"We have a saying that that the sea brings back whatever it takes," says Shridhar Wadekar, an elderly villager. "But for the past two years, I have been waiting for it to bring back my rice farm."

VULNERABLE REAL ESTATE

While poor communities along the coast are the first to have been hit, the super-rich of Mumbai are likely to be affected too. Consultants Jones Lang LaSalle Meghraj recently noted that Mumbai accounts for 40 percent of the $100 billion in Indian construction projects underway.

Property in Mumbai is astronomically expensive because the 100 sq km (39 square mile) island city is located at the southern tip of a peninsula and cannot expand. Coastal multi-storey apartments are in the greatest demand, with high-end apartments now selling for as much as $7 million.

Mumbai also has the highest proportion of land reclaimed from the sea of any old city core in the world. The reclamation was led by rampant speculation during the British Raj in the 18th Century and was only halted by environmentalists in the 1970s. The filling has already caused severe erosion of properties in the northern suburbs as the displaced ocean bites elsewhere along the coast.

After the 2004 Asian tsunami, which impacted only India's deep south, Mumbai authorities erected three-metre-high walls along shallow-water fishing village coasts to the north of the city, even though the villages had been unaffected.

Environmentalists criticised the Canute-like gesture as both ineffectual and a thinly-disguised attempt by officials to line their pockets from sea wall contracts.

TUBE TECHNOLOGY

The latest protection project being undertaken by the Maharashtra government uses "geo-textile tubes", which it says are an eco-friendly method of arresting erosion by keeping sand in place. The tubes are already being used in Kerala and Goa.

The tubes - hollow plastic pipes - will be submerged and placed over sand-filled coconut fibre bags to form a semi-circle, creating an artificial bay. It is hoped marine creatures will be able to get a toehold on the resulting reef-like structure.

The state has identified 72 km (45 miles) south of Mumbai - one tenth of the total length of the coast - as subject to high erosion, and it plans to protect the plantations and fish drying grounds of coastal villagers in this area.

The Asian Development Bank is providing loans to cover $104 million of the total project cost of $179 million. The state government will lend $58 million, and the remaining $17 million will come from private investors, who are looking to sell the tubes, particularly if the technique is replicated elsewhere in the state and in the rest of India.

Yet experts warn the technology must be deployed with care. P.K. Das, an architect and activist who has helped "nourish" a strip of eroded beach in midtown Mumbai with Dutch technology that uses partial barriers to stop sand erosion, says that if the geo-textile tubes are too large, they can interfere with the natural movement of sand and tides.

The state should first conduct modeling experiments to establish sand movement patterns, Das says. Otherwise the tubes could act like dams, arresting natural processes.

"Sand is never static," he explains.

Darryl D'Monte, former editor of The Times of India in Mumbai, heads the Forum of Environmental Journalists of India and is the founding President of the International Federation of Environmental Journalists. He is based in Mumbai.