A natural, low-tech solution to tsunamis: mangroves

The coastal trees and shrubs saved hundreds of lives in India by protecting villages from the waves.

As nations around the Indian Ocean discuss plans for a tsunami early-warning system, environmental scientists here point to an existent, natural form of disaster minimization: mangrove forests.

The coastal trees and shrubs saved the lives of hundreds of people last month, and could save thousands more in the future if further cultivated.

Mangroves form a natural barrier between villages and the roiling sea, and could offer a reliable backup to any new international effort to coordinate warnings and draw up evacuation procedures.

"For thousands of years, mangrove forests have provided a natural buffer against cyclones and other storms that often hit the shores of southern India," says V. Selvum, project director of the MS Swaminathan Research Foundation in Madras (Chennai).

Mr. Selvum says that 172 families were saved from the tsunami in the fishing village of Thirunal Thoppu in India's Tamil Nadu state only because the mangroves are thriving and dense there. He also mentions three other Tamil Nadu villages where damage had been minimized by the aquatic trees.

"Every village has more than 100 families, so just think of the number of lives saved," he says.

One recent CNN story told of a baby boy in Thailand who was saved by the mangroves when the water rushed in and out destroying everything else in its wake.

"Even though the mechanical impact of a tsunami is enormous, and is bound to destroy the first line of mangroves, the water suddenly slows down as it moves farther in," Selvum says.

Mangroves disappearing

For the last 70 years mangroves, which are abundant at river mouths, have been severely depleted as villagers chop them down for fuel and fodder. The dried up areas then absorbed sea water, which in turn increased the soil's salinity and destroyed other vegetation.

The MS Swaminathan Research Foundation has found a way to reverse this problem by channeling the sea water out and bringing the fresh water in. The foundation, which began 14 years ago, works to conserve and regenerate coastal mangroves along India's eastern shores as well as transfer salt-tolerant genes from the mangroves to selected crops grown on the coast.

Recognizing their work, the Indian government began a joint Mangrove Management Project in the 1990s, in local communities all along the east coast from Tamil Nadu to West Bengal in seven mangrove ecosystems.

"We restored about 5,000 hectares while the government restored 10,000 hectares," says Selvum.

The Indian Ministry of Environment and Forests now has a mangrove restoration program which is continuing with the help of local communities on the coast.

"We have a lot of degraded mangrove [areas] in Tamil Nadu - almost one-third of the mangrove area in the state is destroyed completely. It's only now that the local communities, who barely listened to us before, are now seeing the use of the mangroves, which also help to preserve fishing waters," says Sridharan, a Tamil Nadu forestry official.

One of Sridharan's workers was caught offshore in Cuddalore district when the tsunami struck. He made his way back on the boat by entering a mangrove swamp.

"If he had chosen another way, he would surely be dead," says T.K. Sridharan.

A thin barrier left

According to Sridharan, mangroves form only 62 miles of the 620-mile Tamil Nadu coastline. If well looked after, they could save thousands of lives if their density is at least 70 percent in places.

"They must be grown very thickly together to have any use as barriers," Sridharan explains.

Bittu Sehgal, a feature editor and ecologist at Sanctuary magazine, told the Indian Express newspaper that he firmly believes the famous mangrove reserve of the Sundarbans in West Bengal saved the coastal part of the state from severe losses.

"The forest officers on duty have reported there that the water level rose by three to five feet when the tsunami hit. But this is nothing abnormal as we can see 10- to 12-foot high tides on the Sundarbans coast. The mangroves saved us," he says.

Environmentalists say that to focus exclusively on mangroves would be a mistake.

"We need many more coastal shelter belts that stop the intrusion of salt water, like casuarinas and acacia trees," says Selvum. "But, as usual, it is very late in the day."

Regenerating mangroves can take five to six years. In the meantime, New Delhi is pursuing other tsunami systems that can be in place faster. The Indian government has decided to install about 12 deep ocean assessment and reporting systems that will work in coordination with the Pacific Tsunami Warning Center in Hawaii. The cost is expected to run between $22 million and $28 million. The US Congress is also considering a $30 million global tsunami warning network. The plan would build on the Pacific system and other proposed efforts.

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