1.
Welcome…. 

2.
GyanBikash.com presents a
report on……….
Riverbank Erosion
In Bangladesh…
This presentation is owned by
ABUL KALAM AZAD PATWARY
Assistant teacher of Lakshmipur govt girls high
school(English)
“for class 9-10”

3.
Riverbank Erosion an endemic and
recurrent NATURAL HAZARD in Bangladesh.
When rivers enter the mature stage (as in
the case with the three mighty rivers, ganges,
brahmaputra and meghna) they become
sluggish and meander or braid. These
oscillations cause massive riverbank
erosion. Every year, millions of people are
affected by erosion that destroys standing
crops, farmland and homestead land. It is
estimated that about 5% of the total
FLOODPLAIN of Bangladesh is directly affected
by erosion. Some researchers have reported
that bank erosion is taking place in about 94
out of 489 upazilas of the country. A few
other researchers have identified 56 upazilas
with incidence of erosion. At present, bank
erosion and FLOOD hazards in nearly 100
upazilas have become almost a regular
feature. Of these, 35 are severely affected.

4.
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 bankline
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. The unpredictable shifting behaviour of the
rivers and their encroachments not only affect the rural
floodplain population but also urban growth centres and
infrastructures.

5.
Building sloping down…due to river bank erosion..


6.
Children looking down, standing in a risky way. One day which were their
place and shelter, but they lost everything.

7.
Old man pointing towards the water and describing how he
lost his home because of river erosion.

8.
People standing anxiously and looking the river erosion.

9.
No systemic pattern has yet been observed of
the erosion hazards because of the
involvement of a large number of variables in
the process. The intensity of bank erosion
varies widely from river to river as it depends
on such characteristics as bank material,
water level variations, nearbank flow
velocities, planform of the river and the
supply of water and sediment into the river.
For example, loosely packed, recently
deposited bank materials, consisting of SILT
and fine SAND, are highly susceptible to
erosion. Rapid recession of floods accelerates
the rates of bank erosion in such materials.

10.
Specific rivers of Bangladesh
which mainly cause river
erosion are,,….

11.
The Jamuna…….

12.
The Jamuna is a braided river with bank materials that are highly
susceptible to erosion. 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 (68m for the left
bank and 60m for the right bank). The annual rate of widening has
been as high as 184m during 1984-92, of which 100m occurred along
the left and 84m along the right bank (Table 1). In this period, the
average width of the river increased from 9.7 to 11.2 km (Table 2).
The maximum bank erosion during 1984-92 occurred at the left
bank, just upstream of Aricha. Both rotation and extension bank
erosion mechanisms do occur.

13.
The Jamuna has persistently widened from 1973 to the early
nineties, but the yearly rate seems to have gone down
significantly in the late nineties. The widening of the river in a
28-year period resulted in a loss of floodplain of 70,000 ha over
the total 220 km length of the river in Bangladesh (average
about 2,600 ha/year). Within the 1984-92 period, the river has
eroded 40,150 ha of floodplain and accreted 7,140 ha,
corresponding to an erosion rate of about 5,000 ha/year, and
an accretion rate of about 900 ha/year.
In recent years, human interventions in the Jamuna are
growing. Construction of the Bangabandhu Jamuna Bridge,
and bank protection structures at Sirajganj, Sariakandi and
Bahadurabad will doubtless have some influence on the
changes of the width of the river. These types of structures are
reducing the freedom of the river to widen through bank
erosion.

14.
The Ganges…

15.
The Ganges the bank material within the active corridor of the
Ganges consists of loosely packed sand and silt. These materials
are highly susceptible to erosion. The bank erosion process along
the Ganges is controlled mainly by its wandering planform
characteristics. In the braiding reaches, the river can erode along
both banks, as can be seen in the reaches downstream of the
HARDINGE BRIDGE. Maximum bank erosion, however, occurs in
the meandering reaches, where the outer bend can still migrate
laterally within the corridor. In the period 1984-93, the
maximum observed rate was 665 m/year. Along the right and
left bank of the Ganges, erosion rates are 56m and 20m per year
respectively, which is lower than the rates observed in the
Jamuna. The width of the river varied from 1.7 to 10 km in 1984
and from 1.9 to 11.7 km in 1993. The average width of the river in
1984 was 4.37km, which increased to 4.69 km in 1993. 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.

16.
The Padma…….

17.
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
width of the river varied from 3.7 to 8.5 km during 1984 and from 2.7 to 10.7 km
during 1993. The narrowest sections of 3.7 and 2.7km remain at Baruria,
downstream of the confluence with the Jamuna for the period 1984-93. 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. Though less than what was observed in
the case of the Jamuna, the widening of the Padma during the period 1984-93 was
quite significant.
The part of the Padma between its confluence with the Jamuna and the Meghna has
been undergoing significant physical changes in recent decades. The Padma has
widened between 1973 and 1998 by the order of several kilometres. Banklines of the
river are very unstable.
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. This,
in turn, may have accelerated the bank erosion by directing more and more of the
finer flow towards the banks. Between Ramakrishnapur and Dohar the Padma is
fairly wide with major erosion going on along the left bank.

18.
The right bank of this reach near Faridpur moved to and fro while the left bank near
Horirumpur showed a progressive retreat towards the northeast between 1973 and
1998. The left bank has moved several kilometres northeast near Horirumpur, where
an acute erosion problem exists. This is also the point of the ichamati off-take, which
is a small northward distributary of the river.
The part of the Padma between the downstream of Dohar and Mawa has the similar
width as above but differs in terms of location of major bank erosion, which is taking
place along its right bank. Due to the formation of a large bar near the mouth of the
arial khan river, the main flow of this reach is diverted along the right bank and
strikes along Mathbarer Char, which shows severe erosion. Between Mawa and
Louhojong, the Padma is very narrow. Here, the absence of any major bar close to
the bank allows relatively free flow of the water along the channel and does not cause
any flow diversion or concentration towards the bank. Between the downstream of
Louhojong and Munshiganj the river is wide and has many in-channel bars. This
part has the distinction of including most parts of the confluence of the Padma and
Meghna rivers. Some of the largest stable bars are located here. Therefore, the
intensity of bank erosion is controlled by the development of mid-channel bars and by
the diversion of the main channel towards the riverbanks.

19.
Physical characteristics of the Padma and its
distributaries are changing due to oscillation
of the riverbanks, levee breaching and
formation of mid-channel bars. River depths
became shallower at places. Many of the
offtakes were closed due to depositions of huge
sediments at their mouths. Unstable
riverbanks are a threat to the development of
infrastructures, like the proposed Padma
bridge, which are essential for the
development of the entire southwestern region
of the country.

20.
The Upper Meghna…..

21.
Unlike the other main rivers of
Bangladesh, the Upper Meghna is a
stable and seemingly inert river. The
width of the river varied from 1 km to 11.5
km in 1984, while the range of variation
was 1 to 11.3 km in 1993. The high spatial
variation of width is due to the presence
of a permanent CHAR, with a width of
more than 9 km. The average width of
the river in 1984 was 3.41 km while in
1993 it was 3.39 km. Average bank
erosion rates along the right and left
banks of the river were found to be 9m
and 7m per year respectively.

22.
The Lower Meghna…..

23.
after the Padma broke through the
Chandina alluvium and joined the Meghna
at the present confluence about 150 years
ago, the Lower Meghna had to adjust to
carry the combined discharge of the
Jamuna, Ganges and Meghna rivers. The
confluence of the Upper Meghna and the
Padma can be considered as part of the
Lower Meghna. The confluence consists of
a wide cluster of chars bounded by two
channels. The highest width of the
confluence is 14.4 km. Its average width
varied from 7.98 in 1984 to 9.01 km in l993,
reflecting a widening rate of about 100
m/year.

24.
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. The average width of the river in the downstream reach was 5.74
km in 1984 and 8.82 km in 1993.
The river has eroded both its banks, causing formation of medial bars.
Downstream of Chandpur, the westward bank erosion during the
period 1984-1993 was severe, with the rate of erosion at times getting
as high as 824 m/year. 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 the same period (184 m/year).

25.
Socio-economic impact..

26.
Riverbank erosion has disastrous socio-economic effects. The majority of
the affected people perceive riverbank erosion as a natural phenomenon
but in many cases the people believe erosion to be the ‘will of God’.
However, these days, riverbank erosion is seen as one of the major causes
for national poverty. The degree of economic loss and vulnerability of
population due to bank erosion has dramatically increased in recent years.
The impact of land loss involves primarily the loss of homestead land,
housing structures, crops, cattle, trees and household utensils. Loss of
homesteads forces people to move to new places without any option and
puts them in disastrous situations. About one million people are directly
affected each year by bank erosion in the country. The total monetary loss is
estimated to be approximately $500 million a year. An estimated 300,000
displaced persons usually take shelter on roads, EMBANKMENTs and
government-requisitioned lands. Bank erosion affects people, irrespective
of farm sizes. Riverbank erosion causes setback for village agriculture.
Along with homestead settlements, it erodes farmland, infrastructure and
the communication system. It affects the crop income of vulnerable groups.
The big farmers are the worst affected, followed by medium farmers, and
marginal groups. The affected people lose their assets and are forced to
draw on savings and often fall into further debt. Researchers found that the
land lost is much more than the land that rises out of riverbed through
accretion. This erosion-accretion phenomenon is a characteristic feature of
the courses of the rivers in Bangladesh and gives rise to a lot of tension in
local politics.

27.
Displacement is the immediate impact of riverbank erosion. The displaced
usually move to nearby areas but migration to distant places are not
uncommon. In erosion-prone areas, most families have witnessed a
displacement in their lifetime. This involuntary movement can go up to 10
times or even more. A survey conducted in two Dhaka slums has revealed
that they consist of migrants who mostly originated from the districts of
Faridpur (34%), Barisal (25.6%), Comilla (24.3%) and Dhaka (14.3%). A
closer examination of this distribution further revealed that most of the
migrants came from an area consisting of only a few Upazilas mostly located
around the Ganges-Padma and the Meghna and their combined estuaries.
The displacement caused by erosion, mostly involve displacement of whole
families. On an average, a household experienced riverbank erosion 2.33
times in the life of its members. Some of them experienced displacement 4-5
times or more. Most of the environment-induced refugees turn mainly into
laborers or rickshaw pullers. A large proportion of the victims remain
unemployed due to lack of work opportunities. Moreover, women head
many of these families. The female-headed households displaced by
riverbank erosion and residing on embankments are the most deprived
group. Fortunately, nowadays, social workers are focusing on these
problems and also suggesting strategies of survival to these people.

28.
Thank you ..