[Assam] article : Bangladesh Floods: Brahmaputra vs Missisipi river

Thu Jul 5 19:27:50 PDT 2007

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/

---------------------------------
 New Yahoo! Mail is the ultimate force in competitive emailing. Find out more at the Yahoo! Mail Championships. Plus: play games and win prizes.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.assamnet.org/pipermail/assam-assamnet.org/attachments/20070705/ea31b7d9/attachment.htm>