Tuesday, March 31, 2009

Faulty engineering work led to Matmora breach’

A section of the State’s senior water resources engineers is of the opinion that the spacing of the bullhead spurs in the Matmora area and their not being linked up with the un-submersible riverbank, resulted in intense erosion activities of the Brahmaputra in that area.These engineers also maintain that initially erosion of the Brahmaputra in Matmora area was triggered by the Railways’ closing of the Brahmaputra channel near Kareng Chapori, which is located at the upstream of Matmora.

The channel was hugging the north bank. The channel’s closure resulted in erosion in the downstream areas.All these features need careful study while planning and executing any anti-erosion project afresh in Matmora area, said these engineers. It needs mention here that the Water Resources Department (WRD) of the State constructed three river-stone bullhead spurs in Matmora area in 2002-03. Those spurs were aimed at pushing the deep channel of the Brahmaputra away from the north bank to the middle of the river course.The spacing of the bullheads was such that big gaps were left amid the structures enabling the river channel to flow with unhindered intensity. The design so far as these gaps were concerned, contradicted the acceptable engineering norms. Moreover, the spurs were not linked to the bank. The practice of linking the spurs to the unsubmersible bank, with proper fortification, is crucial so as to prevent their outflanking by the river, said the engineers.

Consequently, during the early waves of the 2003 floods, the downstream end bullhead came under intense onslaught of the Brahmaputra. The rear end of the bullhead had to bear the brunt of the flood waters.And in 2004, this bullhead was outflanked and the bank itself became vulnerable to the Brahmaputra onslaught. For the entire rainy season that year and also in the next year, this process continued and by the end of 2005, all the bullheads were outflanked by the Brahmaputra.The strong bank of the bullheads now came inside the river and these structures, built to push the deep channel to the midstream, themselves started pushing the river towards the north bank.

This led to repeated breach of the embankment in Matmora area.The last devastating breach of the dyke occurred in 2008 and it posed grave threat to Dhakuakhana and Majuli subdivisions, said the engineers. On the present history of the erosion in the area, the engineers said that erosion first started near Kareng Chapori, about 20 km upstream of Matmora, around 2000 AD.Since 2000 AD, erosion of the Brahmaputra led to the breach in the Barbil-Kareng Chapori dyke on two occasions.

NF Railway closed the breach in 2002-03. But the flood that occurred immediately after this breach closure, washed away the closed portion of the dyke.Railways then closed the breach again and simultaneously it started laying the approach road to the north end of the Bogibeel Bridge.

This closed the Brahmaputra channel that was hugging the north bank. This reduced the pressure on the Kareng Chapori, but the pressure of the Brahmaputra on the Matmora area intensified since then, said the engineers.They suggested that the government should take into consideration the history of dyke failure in Matmora area with right earnest to prevent recurrence of such developments in future.

Courtesy:The Assam Tribune,March 25,2009