Official statistics show that the Brahmaputra-Jamuna, a major river system in Bangladesh, has widened to 11.8 km now from 8.3 km in the early '70s, eroding about 87,790 hectares of land.

The Centre for Environmental and Geographic Information Services (CEGIS), an independent analysis wing of the water resources ministry, in a recent study said the widening process of the Brahmaputra-Jamuna still continues owing to long-term effects of the 1950 Assam (India) earthquake of 8.6 magnitude on the Richter scale.

Experts said nearly 800 square kilometres of valuable floodplains have been lost due to erosion along the Brahmaputra-Jamuna's total length of 240 km in Bangladesh.

"Around 10 lakh people have become homeless and infrastructures destroyed due to riverbank erosion in the Brahmaputra-Jamuna," said Knut Oberhagemann, team leader of the Jamuna-Meghna River Erosion Mitigation Project (JMREMP), while taking to The Daily Star.

The rate of erosion becomes high and the flow of water strongly hits the river banks when huge quantities of sediment are mixed with water, experts noted.

"Assam earthquake delivered approximately 45 billion cubic metres of sediment to the Brahmaputra-Jamuna river and its tributaries in the Assam valley, raising the riverbed by three metres," said CEGIS Morphologist Maminul Haque Sarker. He conducted a research titled 'Prediction for Bank Erosion and Morphological Changes of the Jamuna and Padma Rivers 2005'.

Around 60 to 70-square km land is being devoured by the Brahmaputra- Jamuna , leaving 60,000 to 75,000 people landless every year, said a research report of Water Resources Engineering department of Bangladesh University of Engineering and Technology (Buet).

"Depth of the Brahmaputra-Jamuna continues to decrease and its width increases. At present, from 100 to 500 metres of land is being eroded from both banks of the river due to lack of river training," said Professor M Monowar Hossain, who conducted the research identifying three causes of expanding width of the Brahmaputra-Jamuna.

Hundreds of small shoals have emerged changing the course of the river as it carries a huge quantity of sediment from the upstream, Monowar told The Daily Star.

"The mighty Brahmaputra deposits large quantities of fertile alluvial soil as it flows for 1,800 miles (2,900 km) from its source in the Himalayas. Sand, stone, mud and varieties of trees merge with water as the river passes through Tibet in China and Arunachal and Assam states of India," he said.

The river also gets widened as it has less slope and carries most of the sediment at bottom level in the water, he added.

According to the CEGIS study, the Brahmaputra-Jamuna had eroded 87,790 hectares of land during 1973-2004 and 12,490 hectares were accreted during the period.

"A total of 1,115 hectares of land was eroded along the right bank and 1,490 hectares on the left bank of the river in 2004," Maminul said. Moreover, 1,442 metres of district roads and 5,104 metres of embankments were eroded during the year.

"Erosion was the highest in Sirajganj (19,250 hectares) and Kurigram (19,110 hectares) and the least in Manikganj (5,770 hectares) and Pabna (3,093 hectares) during the last 31 years," the morphologist said referring to the study.

Knut Oberhagemann found river erosion as major threats to the country's two major irrigation projects -- Pabna Irrigation and Rural Development Project (PIRDP) and Meghna-Dhonagoda Irrigation Project (MDIP) -- which helped Bangladesh grow more crops on less land.

"Now we're trying to save these infrastructures by protecting river banks from erosion using low-cost technology of stacking sand-full geo-bags," he said.

Erosion has also a strong bearing on the livelihood of thousands of people in the districts along the porous 4,000-plus km Indo-Bangladesh border, experts said. They also pointed to the ground reality that erosion on both banks of the transboundary rivers quite often creates tension.

In the most recent case, Bangladesh's border force the BDR in an amicable settlement with the Border Security Force (BSF) of India on Sunday reclaimed the country's stake on 50 acres of land at Ramgarh in Khagrachhari. The land was under disputed possession for long due to erosion of the Feni river's bank inside Bangladesh.

Tauhidul Anwar Khan, a long-time Member of the Joint Rivers Commission (JRC), said it is very much within the mandate of the JRC to protect vulnerable cross-boundary river banks both within Bangladesh and India.