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Expert view: �Silt flow will negate dredging in Brahmaputra�

By AJIT PATOWARY
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GUWAHATI, June 2 - Immediate flow of silt would negate the impact of dredging in the Brahmaputra and its tributaries, asserted US-based senior engineer Dr Umesh C Tahbildar. The Assam-origin engineer was talking to this newspaper.

Nullifying dredging as a potential solution to the nagging flood problem in Assam, Dr Tahbildar maintained that the recently announced plan to dredge the Brahmaputra is not backed by any scientific and engineering data that establish the viability of the project. Moreover, the avowed project cannot guarantee mitigation of the flood problem, he said.

He further asserted that to lessen Brahmaputra flood by reducing only one foot from its high stage of flood at Pandu, a simple calculation shows that the needed embankment cross section will be excessively and prohibitively large in order to utilise the dredged material.

Therefore, the concept does not seem practical. Additionally, no sooner the dredging is done to dig a channel of 35-metre width, as postulated, than the silt-laden flood water of the Brahmaputra will fill the dredged channel to force dredging again. It is going to be a daunting task, both financially and practically. Justification and more clarity from the authorities are needed before the project is launched, the engineer said.

He claimed that it is universally accepted that the only method of really controlling the floods in Assam is the detention of the floodwater in storage reservoirs and subsequent release of the water in a regulated fashion. A thorough analysis of flood plain, precipitation, topography, etc., should be included in mathematical modelling of flow of surface run-off to arrive at optimum locations of the floodwater reservoirs. Other than reservoirs on the tributaries upstream, it will be necessary to have reservoirs to impound flood water at other strategic locations.

All 26,000 villages of Assam should be considered for areas earmarked for detention basins. At the end of the day, pumping will be needed to throw the excess water in appropriate channels bypassing the flood plains. A network of channels or pipelines will be needed for this. As to impounding floodwater at the source of Brahmaputra tributaries, it is quite unfortunate that there isn�t a single large reservoir for flood control in Assam or Arunachal Pradesh. This clearly reflects a lack of will or wisdom on the part of the authorities to solve the State�s flood problem.

To have a viable plan for flood control, actions must be formulated to negate all causes of floods in a concerted effort. The fundamental principle should be to ease away the floodwater by containing it within the flow channels of rivers and streams, and by channelling surface run-off in a variety of ways, observed the US-based senior engineer.

Even after due diligence is exercised in the right earnest to solve the flood problem, there will always be unusual situations � like cloud burst, blockage of rivers and then sudden release of water as the blockage is removed, among others. Provisions must be in place for the affected people to cope with such situations, he said.

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Expert view: �Silt flow will negate dredging in Brahmaputra�

GUWAHATI, June 2 - Immediate flow of silt would negate the impact of dredging in the Brahmaputra and its tributaries, asserted US-based senior engineer Dr Umesh C Tahbildar. The Assam-origin engineer was talking to this newspaper.

Nullifying dredging as a potential solution to the nagging flood problem in Assam, Dr Tahbildar maintained that the recently announced plan to dredge the Brahmaputra is not backed by any scientific and engineering data that establish the viability of the project. Moreover, the avowed project cannot guarantee mitigation of the flood problem, he said.

He further asserted that to lessen Brahmaputra flood by reducing only one foot from its high stage of flood at Pandu, a simple calculation shows that the needed embankment cross section will be excessively and prohibitively large in order to utilise the dredged material.

Therefore, the concept does not seem practical. Additionally, no sooner the dredging is done to dig a channel of 35-metre width, as postulated, than the silt-laden flood water of the Brahmaputra will fill the dredged channel to force dredging again. It is going to be a daunting task, both financially and practically. Justification and more clarity from the authorities are needed before the project is launched, the engineer said.

He claimed that it is universally accepted that the only method of really controlling the floods in Assam is the detention of the floodwater in storage reservoirs and subsequent release of the water in a regulated fashion. A thorough analysis of flood plain, precipitation, topography, etc., should be included in mathematical modelling of flow of surface run-off to arrive at optimum locations of the floodwater reservoirs. Other than reservoirs on the tributaries upstream, it will be necessary to have reservoirs to impound flood water at other strategic locations.

All 26,000 villages of Assam should be considered for areas earmarked for detention basins. At the end of the day, pumping will be needed to throw the excess water in appropriate channels bypassing the flood plains. A network of channels or pipelines will be needed for this. As to impounding floodwater at the source of Brahmaputra tributaries, it is quite unfortunate that there isn�t a single large reservoir for flood control in Assam or Arunachal Pradesh. This clearly reflects a lack of will or wisdom on the part of the authorities to solve the State�s flood problem.

To have a viable plan for flood control, actions must be formulated to negate all causes of floods in a concerted effort. The fundamental principle should be to ease away the floodwater by containing it within the flow channels of rivers and streams, and by channelling surface run-off in a variety of ways, observed the US-based senior engineer.

Even after due diligence is exercised in the right earnest to solve the flood problem, there will always be unusual situations � like cloud burst, blockage of rivers and then sudden release of water as the blockage is removed, among others. Provisions must be in place for the affected people to cope with such situations, he said.