The 'Prediction of Riverbank Erosion along the Jamuna, the Ganges and the Padma Rivers in 2018' report described the loss of an estimated 162,019 hectares (625.558 square miles) of land through erosion since 1973 as 'one of the major natural disasters in Bangladesh'
An area of land roughly five times the size of Dhaka has been lost to the Padma and Jamuna rivers in Bangladesh over the past 45 years, a report of the Center for Environmental and Geographic Information Services (CEGIS) has revealed.
The “Prediction of Riverbank Erosion along the Jamuna, the Ganges and the Padma Rivers in 2018” report described the loss of an estimated 162,019 hectares (625.558 square miles) of land through erosion since 1973 as “one of the major natural disasters in Bangladesh”.
“Riverbank erosion causes untold miseries every year to thousands of people living along the banks of the rivers of Bangladesh,” the report said. “The majority of slum dwellers in large urban and metropolitan towns and cities are victims of riverbank erosion.”
CEGIS Deputy Executive Director Dr Maminul Haque Sarker said that they had divided the Padma River into two parts – the Ganges and the Padma – based on the characteristics and water flow.
“About 200-250 years ago, when the water of Jamuna was flowing through the Old Brahmaputra, the Padma River used to flow up to Chandpur, but when Jamuna met the Padma near Goalundo Ghat, its characteristic changed,” he told the Dhaka Tribune.
“Officially it is the Padma but due to technical reasons, we had to divide it into the Ganges and the Padma. The upper part is the Ganges and lower part is the Padma. The Padma carries three times more water than the Ganges.”
Between 1973 and 2017, the net erosion along the 220km long Jamuna River was about 93,302 ha. During this period, the accretion along the Jamuna was 16,603 ha, the report said.
Sirajganj suffered the worst erosion (23,697 ha) among the districts on the banks of Jamuna, while Pabna recorded the least (2,738 ha) erosion.
From 2015-2017, Sirajganj was also the worst sufferer of riverbank erosion (287 ha), while Jamalpur suffered the least (56 ha).
In 2017 erosion along the right bank of the Jamuna River was 446 ha, of which about 55 ha had settlements. Around 1239m of embankments (969m of active embankments and 270m of inactive embankments) were eroded along that bank. About 1032 m of rural road were also eroded on the right bank.
Erosion along the left bank of the Jamuna River was much higher than that of the right bank, due to the presence of highly erodible materials on the left bank. About 967 ha of land, of which 128 ha had settlements, were eroded last year. About 50m of upazila road and 41m rural road were also eroded along the left bank.
The data show that both banks of the Padma are migrating outwards and that the river is widening. Between 1973 and 2017, the net erosion along the 100km long Padma River was about 37,296 ha.
According to the CEGIS report, the rate of erosion along the Padma varies over time. For example, the rate of widening of the Padma River was 160 metres per year in the 1980s, which increased to 230 m/yr in the 1990s. Recently, the rate of widening has come down to 140 m/yr.
During 1973-2017 period, the total erosion and accretion was 37,296 ha and 14,246 ha respectively. The most affected district was Shariatpur, which lost 9,627 ha. In 2017, Madaripur suffered the most from erosion and lost 517 ha.
In 2017, 1425 ha of land was eroded along the banks of the Padma River eroded , of which about 114 ha had settlements . About 343 m of rural road was eroded.
According to CEGIS, an analysis of the satellite images of the last several decades shows that the Ganges is almost stable in width, even though it is shifting continuously.
Between 1973 and 2017, erosion along the river was 31,421 ha while accretion was 27,026 ha. The most affected district by the Ganges during this period is Kushtia (total erosion is 11,834 ha), the report said.
Erosion along the banks of the Ganges River in 2017 was around 329 ha, of which 21 ha had settlements. Around 169m of upazilla road and 273m of rural road were eroded along the river.
Last year, the maximum erosion took place in Rajbari (199 ha) and the minimum in Pabna (11 ha).
22 riverbank locations ‘vulnerable’
Dr Maminul said CEGIS has quality resources such as high resolution satellite images and Geographic Information System (GIS) technology which made it possible to monitor the extent of river erosion and resulting damage to infrastructure.
“Time series satellite images are being used to monitor and predict bank erosion, while it has developed tools for predicting bank erosion and morphological changes of the Jamuna, the Ganges and the Padma,” he said.
The report promoted the use of erosion prediction tools since structural interventions to provide protection against riverbank erosion are very costly.
“Less costly nonstructural measures such as erosion prediction can be used to reduce the loss due to riverbank erosion and lessen the sufferings of people,” the report said.
Since 2004, the CEGIS has been predicting riverbank erosion of the major rivers in Bangladesh with adequate accuracy in collaboration with the Bangladesh Water Development Board.
For this year, CEGIS has predicted 22 probable vulnerable locations along the banks of the Jamuna, Ganges and Padma. Fifteen of these locations are located on the banks of
Jamuna, four in the Ganges, and three in the Padma.
The riverbank erosion is predicted to occur in 11 districts along the banks of the major rivers. These districts are: Kurigram, Gaibandha, Bogra, Sirajganj, Tangail, Manikganj, Rajbari, Rajshahi, Faridpur, Shariatpur and Madaripur.
“The prediction is not only limited to the identification of vulnerable locations but also provides information of the vulnerability of the land, settlement and other physical infrastructures of the predicted locations,” Dr Maminul said.