Guwahati, Thursday, June 24, 2010
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ADB, river engineers differ on geo-bags
AJit patowary
 GUWAHATI, June 23 – Resentment prevails among the river engineers here over the persistent pressure from a powerful lobby in the Asian Development Bank (ADB) for use of geo-bags to resist Brahmaputra erosion in Palasbari-Gumi and Dibrugarh. It needs mention here that the State Government is working on a scheme to protect Palasbari, Bankuwal (Kaziranga) and Dibrugarh town with an ADB loan.

The lobby is mounting pressure for use of geo-bags in the form of bank revetment. Bank revetment is generally not adopted in Brahmaputra because of many reasons. Most important of them is – it produces a permanent deep channel along the existing riverbank. Moreover, revetment requires huge quantity of material and is a costly affair, said the river engineers.

Assam has lost about seven per cent of its land to the Brahmaputra only because of the lack of funds and absence of adequate technology in the past. But now, Assam has cheap and successful systems and no international technology can match it, claimed the river engineers here.

They have alleged that the ADB provided 23,000 geo-bags for an experiment. They were dumped in the month of September 2009 at a 150-metre-long selected erosion-prone reach at Gumi for testing their efficacy.

But, a diving observation made in the month of December 2009, suggested that the bags were not launched uniformly in a single layer as it was claimed. They were found lying in a haphazard manner in staggered heaps with gaps in between and the total distance they covered was only about 8 metres, against the claimed and required 35 metres.

Meanwhile, ADB made a lot of endeavour to convince the Central Water Commission (CWC) for use of geo-bags. This resulted in the sending of a team of engineers to Bangladesh to study the application of the geo-bags there. But river engineers on the tour found it difficult to arrive at any decision by seeing things done in diametrically different geo-morphological, hydrological etc conditions.

The ADB then carried out another diving observation at Gumi in May last and found no bag at the site. The State WRD did not get any feedback from the ADB on this issue.

But the CWC stunned the river engineers here with a letter the same month. The letter quoted the ADB as indicating that possibly due to the silt deposits over the geo-bags, these structures were not found during the May diving exercise. Therefore, the letter said, the WRD ‘may consider’ providing four layers of geo-bags and resubmit the detailed project reports (DPRs) (to the CWC) accordingly.

The river engineers here find the argument of silt deposits taking place in the month of May, that too, over the hard surface of geo-bags, as an absurd one. As, they maintain, hard surface normally cannot attract silt.

The most important thing is that the site where the geo-bag test was carried out is under active erosion and the riverbank has eroded by about 20 metres in the month of May when diving was carried out.

In the mean time, it is learnt that the DPR for Dibrugarh has been modified with provisions for geo-bags, going against the recommendations of the Technical Advisory Committee (TAC) of the WRD. The DPR has been submitted to the CWC, said the engineers.

The TAC is a multi-disciplinary standing body under the Assam State Brahmaputra Valley Flood Control Board (ASBVFCB). It is the apex body for the WRD in respect of the technical matters. The Chief Minister of Assam chairs the ASBVFCB. Accordingly, the TAC is the advisory technical body to the Chief Minister too and the WRD cannot change the TAC recommendations without its (TAC’s) knowledge.

However, for the Palasbari site, the TAC had a meeting on June 17. In this meeting, the TAC virtually yielded to the pressure to convert the whole of the Palasbari Sub-project into a “Test Sub-Project” at the cost of about Rs.205 crore. Meanwhile, the Palasbari DPR is awaiting modification, said the river engineers.

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