Saturday, March 21, 2009

In Silt, Bangladesh Sees Potential Shield Against Sea Level Rise

Photo Saiful Huq Omi/Polaris, for The New York Times: In Beel Bhaina, a low-lying 600-acre soup bowl of land on the banks of the Hari River, in Bangladesh, land that was once under water is now full of greenery
SOMINI SENGUPTA

BEEL BHAINA, Bangladesh — The rivers that course down from the Himalayas and into this crowded delta bring an annual tide of gift and curse. They flood low-lying paddies for several months, sometimes years, at a time. And they ferry mountains of silt and sand from far away upstream.

Most of that sediment washes out into the roiling Bay of Bengal. But an accidental discovery by desperate delta folk here may hold clues to how Bangladesh, one of the world’s most vulnerable countries to climate change, could harness some of that dark, rich Himalayan muck to protect itself against sea level rise.

Instead of allowing the silt to settle where it wants, Bangladesh has begun to channel it to where it is needed — to fill in shallow soup bowls of land prone to flooding, or to create new land off its long, exposed coast.

The efforts have been limited to small experimental patches, not uniformly promising, and there is still ample concern that a swelling sea could one day soon swallow parts of Bangladesh. But the emerging evidence suggests that a nation that many see as indefensible to the ravages of human-induced climate change could literally raise itself up and save its people — and do so cheaply and simply, using what the mountains and tides bring.

“You can do a lot with the silt that these rivers bring,” said Bea M. ten Tusscher, the Dutch ambassador to Bangladesh. The Netherlands, itself accustomed to engineering its vulnerable low-lands, helps Bangladesh with water management projects. “Those are like little diamonds,” Ms. ten Tusscher said. “You have to use it.”

Satellite images show that in the natural process of erosion and accretion — in some places speeded up by a series of man-made dams and channels — Bangladesh has actually gained land over the last 35 years.

Skeptics say it is folly to expect silt accretion to save the country. Accretion happens slowly, over centuries, they argue, while human-induced climate change is hurtling fast toward Bangladesh. The new land is too muddy and slushy for people to safely live on, and the force of the Himalayan rivers is so powerful that it can wash away newly gained land in one fluke season.

“If you have time to wait, it will happen,” said Atiq Rahman of the Bangladesh Center for Advanced Studies. His country, he added, does not have time to wait.

The silt-trapping experiment has yielded tentative but visible gains here in Beel Bhaina, a low-lying 600-acre soup bowl of land on the banks of the Hari River, a tributary of the Ganges, about 55 miles upstream from the Bay of Bengal. Even at this distance from the coast, it is among the country’s most susceptible to sea rise. The river swells each day with the tides. Creeping salinity in the water table is a harbinger of future danger.

Here, misery made way for a discovery. A devastating flood 10 years ago left this soup bowl — a “beel” in Bengali — inundated with water that reached above Abdul Lateef’s head. No paddy could grow, recalled Mr. Lateef, now 56. Houses went under. The river was so heavily silted it hardly moved. Many families were reduced to penury.

One night, desperate to drain the water, Mr. Lateef and his neighbors punched a hole through the mud embankment that encircled the soup bowl. They watched as the water rushed out. Then the high tide began to haul in sediment, and the soup bowl swiftly filled with silt.

When the chief engineer of the local water board, Sheikh Nurul Ala, came to measure it, he saw that in four years, Beel Bhaina had risen by as much as three feet or more near the river bank, and almost as much farther inland. Today, it is a quilt of green and gray square patches of paddy, cut by square ponds to cultivate fish and shrimp. The river flows more freely now. Mr. Lateef collects an annual harvest of rice, the local staple, and farms shrimp, the most lucrative cash crop, after the rains.


Mr. Ala is trying the experiment in other soup bowls upstream, with mixed results. At one site, the accretion was too limited; at another, it has been promising in patches, but uneven.

American scientists have recommended a somewhat similar silt diversion program: opening Mississippi River levees south of New Orleans to allow sediment-rich water to flow over the region’s marshes, which have been starved of silt since levee-building began in the region hundreds of years ago.

Bangladesh is among the nations most susceptible to climate change. Already prone to cyclones, it could be hit by more frequent and intense tropical storms. Seawater is creeping into the agricultural land. Its long coast is exposed to the hungry sea.

The Intergovernmental Panel on Climate Change estimates that a three-foot rise in sea levels could swallow nearly 20 percent of Bangladesh’s territory. The peril is compounded by the fact that every inch of this densely populated country is settled, even those areas at the constant mercy of the water.

Taming the waters that spill into Bangladesh is no easy task. The rivers change course, banks shift, channels meander at will. They swell when the snows melt thousands of miles away and then again when the clouds burst, turning the green fields gray. They are also heavily engineered upstream: a dam built upstream in neighboring India can critically stanch the flow of freshwater down here, increasingly the chances of salinity and siltation.

The simple silt-trapping engineering here was not designed as an adaptation to sea rise, but Mr. Ala is convinced that it can outpace the projected three-foot rise in sea levels and at least offer some protection. “Some benefit it will provide, I think, by raising the beels,” he said. “The problem will not be as severe for the land we can raise.” #

First published in The New York Times, March 20, 2009