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Bangladeshis are already feeling the effects of climate change, especially those living on the low-lying river delta near the mouths of the Ganges. Frequent floods and stronger storms have been inundating the area with more water than many local rice growers can cope with, driving thousands to seek work in overcrowded cities.

But some rice and shrimp farmers are holding out hope that the very waters that have oft plagued them might hold the solution – in suspension. River silt, carried down in suspension from the ancient Himalayan mountains hundreds of miles away, might be able to build up land elevation to save the area's livelihoods and homes, The New York Times reports today.

In Bangladesh, deposited sediment has been slowly filling the marshy delta outward into the Bay of Bengal for the past few decades, but engineers are examining ways that it might be used to build the land up rather than out, according to the Times. The goal is to allow water to flood some especially low areas and let it out – through dams and channels – slowly. As the murky water slows, sediment drops out and filters to the bottom, leaving a new bed of silt after the water recedes. Residents in Beel Bhaina discovered this phenomenon after releasing stagnant floodwaters through an embankment; to the surprise of many, the Times reports, three feet (or more) of silt had been deposited, boosting land higher above sea level.

"Usually people are trying to get rid of the sediment," says John Gray, a hydrologist at the U.S. Geological Survey. "But here, people are using it as a resource." But Gray is skeptical that it's a viable answer. One major obstacle, he tells ScientificAmerican.com, is that it would require yet more flooding to achieve decent amount of sediment buildup.

"If they're really talking about building land," he says, "the experimental patches are a good start, but they're really going to have to start working on a much large scale."

Gray praises the effort, noting that it's "laudable" to try to "take something that most consider a nuisance" and turn it into an asset. But he warns that if massive quantities of water are diverted, unexpected consequences, such changes in river behavior, are likely to occur. Gray isn't even sure that it's a surefire stopgap against rising sea levels, which are predicted to top three feet by the end of this century. "The timing of accretion [deposit of the sediment] and the timing of the climate change, he says, "might not be compatible."

Centuries of engineering have gone into clearing river channels and mouths of silt to make them more navigable and easier to control. But as rivers have been carved out and dammed for easier navigation, sediment rushes out to sea, rather than getting deposited in the delta. This means many deltas worldwide, including the Mississippi River Delta in Louisiana, the Nile Delta in Egypt, the Yangtze Delta in China and others, are disappearing, leaving costal towns and cities more vulnerable to increasingly strong storm surges. If Bangladesh succeeds in bracing its floodplains this way, it might be a new safeguard for costal areas across the globe. But the proof will be in the (rice) pudding.

Image of Bangladeshi farmers harvesting rice in flooded fields courtesty of the International Rice Research Institute via Flickr

3 Comments

1. 1. Shoshin 09:29 PM 3/21/09

   OK. So now the light goes on. After "centuries of engineering" to clear channels and make the rivers navigable it dawns on them that they have been upsetting the natural course and evolution of the watershed, placing the deltas into a destructive phase.
   
   So the question is how will battling "climate change" help these people if the problem was created by them on a local level through their disturbance of a natural system? Answer: It won't.
   
   Al Gore loses another slide from his Nobel prize winning powerpoint. Thread by thread, the Emperor is inexorably stripped bare.
   
   Finally an article in SCIAM that recognizes something other than political agenda! Bravo to the editor who dug in his or her heels and allowed a balanced article to be published!

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2. 2. muraree 05:00 AM 3/23/09

   Bangladesh lying with mouth of Brahamaputra Delta not on Ganga delta.
   silting or silt deposition at the mouth of Brahamputra delta this is a countinuis proccess of sedimantation but in other way according to Prat/Eiry Isostasy theory , in coming decads or century delta spreading to seaward upto Himalayan erosonal last stage.
   Only dams are man made barriers in the riverin path but this is for limited time- diration . But man is not powerfull than `Natural Geography so, for Bangledesh coming years are time for land spreding

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3. 3. Zainul 01:38 PM 3/24/09

   Bangladesh lies in the mouth of both Brahmaputra and Ganges. water and silt carried by both of these mighty rivers influence life in Bangladesh.
   
   Regarding the accumulation of 3 feet silt in one monsoon period is possible as it often happens in active rivers to form 'charlands' but on a large landscape like 'beels' and 'haors', this could be difficult. Normal flooding may take many years to deposit 3 feet silt in beels and haors. while engineering solutions to Bangladesh's flood and drainage control has positive as well as negative effect on the life and livelihoods. Most often engineering solutions did not take care much of the livelihood issues. Future engineering solutions like this one will need integration of livelihood issues as well.
   

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