Riverbank Erosion is an endemic natural hazard in our country. When rivers enter the mature, they become sluggish and meander or braid. These oscillations cause extreme riverbank erosion. It is a perennial problem in our country. • It has been estimated that tens of thousands of people are displaced annually by river erosion in Bangladesh, possibly up to 100,000. Many households are forced to move away from their homesteads due to riverbank erosion and flood. • As per different sources, 500 kilometres of riverbank face severe problems related to erosion. The northwest part of the country is particularly prone to riverbank erosion, which has turned the region into an economically depressed area.

1. River Bank Erosion, its
Migration, Causes,
Possible Hazards
Presented by
Md. Shahadat Hossain Biplab
Md. Nazim Uddin
S.M. Muhibullah

2. Overview
• Riverbank Erosion is an endemic natural hazard in our country.
When rivers enter the mature, they become sluggish and
meander or braid. These oscillations cause extreme riverbank
erosion. It is a perennial problem in our country.
• It has been estimated that tens of thousands of people are
displaced annually by river erosion in Bangladesh, possibly up to
100,000. Many households are forced to move away from their
homesteads due to riverbank erosion and flood.
• As per different sources, 500 kilometers of river bank face
severe problems related to erosion. The northwest part of the
country is particularly prone to river bank erosion, which has
turned the region into an economically depressed area.

3. River Bank Erosion
• Some rivers cause erosion in large scale and high frequency due
to their unstable character. These rivers assume a braided
pattern consisting of several channels separated by small islands
in their courses.
• During the last 200 years or so, the channels have been swinging
between the main valley walls. During the monsoon, extensive
overbank spills, bank erosion and bank-line shifts are typical.
• The gradual migration or shifting of channels of the major rivers
in Bangladesh amount to anywhere between 60m to 1,600m
annually. In a typical year, about 2,400 km of the bank line
experiences major erosion

4. Causes of River Bank Erosion
• Geological Shape: The flat delta lands of Bangladesh offer little
resistance to the hydraulic forces of its rivers, particularly during
periods of high flow.
• Mature Stage of River: When rivers enter the mature stage they
become sluggish and meander or braid which cause massive
riverbank erosion e.g., GBM River System.
• Sedimentation in the River Beds: The GBM River System carries
about 1.1 billion tons of sediment every year and is responsible
for the prevalence of flooding and riverbank erosion in
Bangladesh.

5. Factors that Accelerate
Erosion
• Stream bed lowering or in fill
• Flooding of bank soils followed by rapid drops in flow
• Saturation of banks from off-stream source
• Redirection and acceleration of flow within the channel
• Poor soil drainage
• Wave action
• Excessive Sand/Gravel Extraction
• Intense water from rainfall

6. Impacts of River Bank
Erosion
• Displacement of people from one place to another.
• Affect in public health
• Educational structure is also negatively changed
• Affect in the occupation of the affected people
• Unemployment Problems can be increased
• Poverty in society
• Affect in the transport system
• Agricultural demotion

7. Impacts of River Bank
Erosion (Cont.)
• Losses crops
• Shortage of cropland
• Increase landless labor
• The salinity of land increases
• Isolation from the geographically of eroded areas
• Acquisition of and by government
• Low investment
• Hinder of capital formation
• Affect productivity in eroded Soils

8. Erosion on the bank of the
Jamuna
• It is highly susceptible to erosion for its braided pattern and bank
materials.
• Since the Brahmaputra switched to the course of the jamuna at
the western side of the madhupur tract, the average width of
the river has fluctuated substantially.
• The recorded minimum average width of the Jamuna was 5.6 km
in 1914. Locally, the maximum width has often exceeded 15 km,
while the recorded local minimum width was about 1.1km.
• The rate of widening of the river within the period 1973 to 2000
is 128m/year

9. Erosion on the bank of the
Ganges
• The Ganges the bank material within the active corridor of the
Ganges consists of loosely packed sand and silt which are highly
susceptible to erosion.
• In the braiding reaches, the river can erode along both banks, as
can be seen in the reaches downstream of the Hardinge Bridge.
• However. maximum bank erosion, occurs in the meandering
reaches, where the outer bend can still migrate laterally within
the corridor.
• The widening rate of the river is 36m/year, which is about one-
fifth of the Jamuna. The widening of the Ganges is not
considered significant.

10. Erosion on the bank of the
Padma
• The Padma bank erosion in the padma is governed by the
planform characteristics of a wandering river. The braided reach
of the river is eroding along both banks, while the meandering
reaches erode only the outer banks.
• The average width of the river varied from 5.7 km in 1984 to 7.1
km in 1993, corresponding to a widening rate of 159 m/year; left
and right bank erosion rates were 121 m and 38m per year
respectably.
• The Padma, traditionally considered a dominantly meandering
system, is switching over into a braided system. The increased
rate of bar development at the Padma may be due to increased
suspended load, particularly the increase of sand fractions.

11. Erosion on the bank of the
Meghna
• The Upper Meghna unlike the other main rivers of Bangladesh, the
Upper Meghna is a stable and seemingly inert river.
• Lower Meghna had to adjust to carry the combined discharge of the
Jamuna, Ganges and Meghna rivers.
• In 1984, the river downstream of Chandpur consisted of a single
thread channel with a large meandering wavelength. But in 1993,
the planform of the river changed to a multi-channeled braided
river.
• The width of the Lower Meghna downstream of Chandpur varied
spatially from 3.82 km to 7.87 km in 1984 and from 5.03 km to
13.00 km in 1993.
• During the same period, the average bank erosion along the right
and left banks were 182 and 66 m/year, respectively, the sum of
which (248 m/year) is higher than the widening rate of the Jamuna
during 1984-93(184 m/year).

12. River Bank Erosion Losses in
Bangladesh
• It is estimated that about 5% of the total
Floodplain of Bangladesh is directly by erosion.
• Bank erosion taking place in 94 out of 489
upazilas of the country.
• At present, bank erosion and flood hazards in
nearly 100 upazilas have become almost a regular
feature. Of these, 35 are sevearly affected.
• Building sloping down due to river bank erosion.

13. Thank You……