http://www.weeklyholiday.net/250703/edit.html
During this season, the monsoon, newspapers dutifully write every year about
the perennial problem of river erosion and the consequent loss to properties.
M. H. Khan, a former Member of the Bangladesh Water Development Board, suggests
to introduce in our country the technology the US applies to protect the banks
of the Mississipi
Erosion prevention and water conservation The water resources of a country
play a very vital role in its economic growth and its sustenance. A river is an
asset only as a controlled river. Its waters form a navigation artery of
tremendous worth as long as the channel is safe and dependable. A river is
beneficial to the area through which it flows as long as it is made to work for
the region and not allowed to destroy it. In fact, water is the lifeline of our
country.
In our country, besides the three major rivers � the Brahmaputra, the
Padma and the Meghna � there are numerous tributaries, distributaries
and small rivers, totalling about 700 (Bangladesh Statistical year book). We
could not obtain desired benefits from these rivers due to these problems: (1)
erosion: erosion of river banks with soft soil and consequent loss of valuable
land, industries and housing estates; (2) drying out of rivers: during the dry
season most of the rivers almost dry out, which affects the national economy
and the supply of water; (3) flood: inundation and consequent damages are an
annual phenomenon. Besides local precipitation, a huge quantity of upland flow
inundates the land, and backwater flow of high tide prevents drainage of the
flow into the Bay of Bengal. Effect of backwater flow is experienced up to
Goalando, Chandpur, Dhaka and Narayanganj.
Suggestions
Protection of river banks against erosion: We have so far failed to provide
effective protection of riverbanks against erosion despite huge expenditure on
this account. In this regard measures normally taken to control bank erosion in
our country are: (i) construction of groynes, permeable and impermeable spurs;
(ii) placing of geo-textile and loading the same with boulders and concrete
blocks; (iii) dumping of boulders, concrete blocks and sand-cement blocks in
the eroding area and placing revetments over sloped banks; (iv) placing of
�porcupine� made of bamboo and bricks; (v) placing of brick
mattress (constructed with bricks and G.I.wire net); (vi) placing of gabions
(filled with bricks or boulders); (vii) construction of hard points; (viii)
geo-textile bags filled with sand, etc. All these efforts have proved futile in
most cases due to various reasons.
So, instead of repelling the river flow through construction of spurs and
groynes, we should concentrate our effort on the protection of the soft soil of
the banks. This is being done in the Mississippi River since 1928. In this case
articulated concrete slab mats of only 3� thickness
(4�x25�size mats each containing 16 slabs) have been used. The
mat not only covers the eroding part of the embankment but also covers
anticipated scour depth. It has proved successful.
It is often argued that our rivers are much bigger in size than that of
Mississippi and our local contractors are not aware of the technology and that
we do not have the needed equipment and expertise for such works. But the size
of the rivers is not the main factor. The velocity and other hydrological
phenomenon are the guiding factors. From the records of the Surface Water
Hydrology Department of the Bangladesh Water Development Board, the maximum
discharge and velocity of our major rivers are as follows:
(a) Jamuna at Bahadurabad: year 1998 � discharge 1,02,535 cumec,
velocity 3.29 m/sec
(b) Ganges at Harding Bridge: year 1998 � discharge 73,091.35 cumec,
velocity 3.765 m/sec
(c) Meghna at Bhairab Bazar: year 2002 � discharge 16,558 cumec,
velocity 1.57 m/sec
(d) Padma at Mawa: year 1998 � discharge 1,16,011,
velocity 4.35 m/sec
The above record shows that the velocity is maximum in Padma at Mawa, but
there is no erosion here due to the sticky clay soil of the bank. So we have to
protect soft soil.
In case of the Mississippi River, only the eroding part of the riverbank is
protected. For this, during the low water stage, the eroding part of the bank
is properly sloped and gravel filter is placed over it. The articulated
concrete slab mats are placed over the filter course and above the water line.
The launching cable ends are properly anchored in the ground. 35 mats
(4�x35=140rft) are connected together on the bank line. This is called a
launch. More mats are connected towards the river and laid over natural
riverbed till the deepest part of the riverbed is reached. A subsequent mat is
placed, overlapping the previous one. The process is continued until the entire
eroded area is covered. As of 1995, 2700 km of eroding riverbanks of the
Mississippi have been protected and 430 km of the meandering length of the
river have been shortened.
The technology is a bit different from what we now practice but our
resourceful contractors can easily acquire the same. The steel forms may be
fabricated locally. The wire rods (stainless steel rods of 3/16�
diameter) required in slab reinforcement are available in the local market. The
3/8� steel wire required as launching cable is also available. Barges
and tugs are available, some cranes are already available and some others may
either be fabricated locally or imported.
Conservation of water during dry season: Conservation of water is possible
through construction of barrages with or without navigation locks. In this
regard the suggested places are (i) Ganges river down the offtake end of Gorai
river, (ii) Jamuna river down the offtake end of Old Brahmaputra river and
(iii) in Ganges-Padma down the offtake end of Arial Khan river, (iv) Dudhkumar,
(v) Dharla, (vi) Mohananda, (vii) Atrai, (viii)Korotoya, (ix) Punarbhaba, etc.
Dredge out deposited silt: There should be an annual programme to clean out
deposited silt and dig out small channels at the offtake ends of each silted-up
river. This can be done with the help of water jets and small suction dredgers,
a number of which can constructed locally with imported engines and pumps.
Construction of barrier dams at the estuary: In order to reduce flood
hazard, intrusion of high tide can be prevented through construction of barrier
dams at the estuary ends across Passur and Meghna as has been done in Thames of
England. With the construction of barrier dams it has been possible to protect
an area of England almost equal to Bangladesh from inundation. This also helps
in the prevention of saline water intrusion and conservation of sweet water at
the estuary�s end.
Control and monitoring body: At present there are many water users but the
government of Bangladesh should authorise only one agency to plan, monitor and
take the above-mentioned measures for effective solution of the manifold water
problems.
Umesh Sharma
Washington D.C.
1-202-215-4328 [Cell]
Ed.M. - International Education Policy
Harvard Graduate School of Education,
Harvard University,
Class of 2005
http://www.uknow.gse.harvard.edu/index.html (Edu info)
http://hbswk.hbs.edu/ (Management Info)
www.gse.harvard.edu/iep (where the above 2 are used )
http://jaipurschool.bihu.in/
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