Tidal river plan could allay climate threat in southwest

Bangladesh stands on the front line of the global battle against climate change, with concerns growing that rising seas could displace millions of people in the south of the country by the middle of the century. An increasing body of evidence is now suggesting traditional river management techniques hold an answer.

Published : 6 Sept 2009, 04:57 PM
Updated : 6 Sept 2009, 04:57 PM
Kamran Reza Chowdhury
bdnews24.com senior correspondent
Dhaka, Sept 4 (bdnews24.com)—Bangladesh stands on the front line of the global battle against climate change, with concerns growing that rising seas could displace millions of people in the south of the country by the middle of the century. An increasing body of evidence is now suggesting traditional river management techniques hold an answer.
Silt pushed upriver from the Bay of Bengal can be an invaluable tool to manage the environment in southwestern Bangladesh comprising five districts.
The populations of Khulna, Jessore, Satkhira, Bagerhat and Narail districts could adapt to rising sea levels if tidal river management (TRM) is practiced in a planned way, say locals and experts.
Locals in the region have resurrected the age-old practice of raising the land through TRM, which has freed hundreds of hectares from water logging caused by massive polderisation (construction of embankments) back in the 1960s.
Although polders have created an environmental disaster in the region, authorities still see the need to build more to combat rises in sea level.
Climate scientists worldwide see the possibility of a one-metre rise in sea levels by 2050, which would inundate 15-20 percent of Bangladesh's coastal belt including the southwest and create millions of environmental refugees.
Low-lying delta
The southwestern districts of Khulna, Jessore, Satkhira, Bagerhat and Narail have a combined area of 15,735 square kilometres. The region is on average two meters above sea level with around 60 rivers dominating the landscape before emptying in to the Bay of Bengal.
The area is formed by sediment from the natural ebb and flow of the river systems, while the floodplains are dotted with thousands of shallow water bodies or beels.
Natural process hampered
The aim of TRM is to allow silt bearing flood tides to inundate floodplains unhindered, resulting in sedimentation of the land. Ebb tides take the water back out to the Bay remove the upper layer of the riverbeds and increase the depth of the river.
This natural process has historically been welcomed by the local population. Flood tides raise the flood plains by new land formation, while ebb tides deepen riverbeds.
But, instead, hundreds of villages in the region have suffered chronic water logging since construction of polders encircling the floodplains.
Why water logging?
Water logging in the southwest goes hand in hand with construction of permanent polders by the government's Water Development Board (WDB), replacing age-old TRM.
In the 1960s, the government, with the financial assistance of donors, built permanent coastal polders in the southwest to combat annual flooding for year-round agricultural production.
However, by the early 1980s polders became a bane rather than a boon for the people, as rivers failed to maintain their natural courses. Tides deposited silt on the riverbeds, rather than the floodplains, for more than two decades, halting the natural flow of the rivers.
The consequent dearth of land formation left floodplains inside the polders lower than riverbanks outside the polders. Rainwater, therefore, could not drain from the areas leading to chronic water logging.
Locals resurrect their land
Aditya Kumar Mondol, a resident of Ambhita village in Khulna district, has become a crusader in the fight against water logging as locals have been tackling the crisis since the late 80s.
In 1992, local residents cut into Polder-25, defying army deployment, and the sluggish Hari River inundated Beel Dakatia, increasing the height of the land and depth of the riverbed as silt was deposited on significant portions of the beel.
Standing in front of his home inside Beel Dakatia, Mondol told bdnews24.com: "My father lost this land to waist deep waters, but TRM has freed it. Now, I am able to support my family."
He said one-third of the population of the area had left the area since the area went under water. "Now almost all have returned home."
In 1997 locals cut another polder in Keshabpur, Jessore, allowing water from the Hari River to inundate Beel Bhaina.
"Almost all 9 square kilometres of land inside Beel Bhaina was free from water logging in 3 years. Now we can grow crops," Asaduzzaman, 45, a resident of Bhorotbhaina village, told bdnews24.com.
Subhas Chandra, another resident of the village, told bdnews24.com his land inside Beel Bhaina had risen a metre in 3 years.
He said more than 1,000 people left the Beel Bhaina area and almost of them returned home when they saw their homesteads freed from water logging.
WDB swayed
According to the WDB, the depth of the Hari River increased by 30 feet since the polder was cut in 1997. Finally, in 2000 the WDB accepted TRM as a method of river management.
It appointed the Institute of Water Modelling to recommend ways to increase the effectiveness of TRM, after which the IWM began studies on the traditional method at Beel Kedaria in 2002 and East Beel Khukshia in 2006.
A recent IWM report to WDB said East Beel Khukshia was "found technically feasible and socially acceptable for tidal river management."
It also said the Beel Kedaria tidal basin became functional in 2002-2004 with deposition taking place over almost the whole 5.24 square kilometre area.
Sheikh Nurul Ala, Jessore WDB superintendent engineer, told bdnews24.com the Asian Development Assistance Board (ADAB) also accepted TRM as a method of river management in 2000.
"We have to spend $142,857 to dredge 15 kilometres of river 30 metres long by two metres depth. But TRM costs next to nothing." Ala said the height of 650 hectares of land could be raised by 13 inches in one year through TRM.
"This is a natural process and environmentally sustainable. TRM is also accepted by the people as the only sustainable method of river management in the southwest region," he said.
Threat of rising seas
The IPCC's 4th assessment report predicts global warming will result in sea level rises of between 0.18 and 0.79 metres by mid-century, spelling disaster for the Bangladesh coast, even though most of the area is protected by polders.
Prime minister Sheikh Hasina, addressing the World Climate Conference-3 in Geneva on Sept 3, said a rise in sea levels of one metre would render 20 million Bangladeshis as environmental refugees.
Ainun Nishat, one of the authors of Bangladesh's Climate Change Strategy and Action Plan, told bdnews24.com, "By applying TRM, we can combat rising sea levels … Bangladesh will have fewer climate refugees." TRM is the only method of river management in the southwest, he added.
Forming new land by breaking existing polders and flooding areas for TRM will take years, although few people are willing to leave even their waterlogged homesteads for such long periods.
Some farmers have therefore demanded the government pay compensation for TRM projects. "If we leave our homes for TRM, where will we go?" farmer Kashem, 50, asked bdnews24.com at Beel Purulipatta in Keshobpur.
IWM's Zahirul Haque Khan, who coordinated the TRM studies, said: "Developed countries have had to fund crop compensation."
"If our farmers are compensated for land formation through TRM we can save thousands of hectares of land from water logging," he said.
"We can adapt to sea level rises and fewer people will lose their homes and land in the long-term."
"The international community too should look to this local knowledge of river management which may be applicable to other parts of the world," said Khan.
Toufique Imrose Khalidi
Editor-in-Chief and Publisher