Panic gripped the residents of the downstream areas of the Subansiri river as rising waters of the river have been flowing over the 2000 MW Lower Subansiri Hydro Electrical Power project at Gerukamukh along Assam-Arunachal Pradesh border since Sunday night.
The river has been in surge due to incessant rains in that area covering the hills of neighbouring Arunachal Pradesh.
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Villagers living in the downstream areas of the Subansiri river in Lakhimpur, Dhemaji and Majuli districts are spending sleepless night.
The LSHEP site at Gerukamukh has been experiencing a series of natural disasters since May 27 with landslides and damages to claddings of the diversion tunnel.
The overflowing Subansiri also inundated many installed machineries and other infrastructure in the LHEP site.
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The developments prompted various organizations to hold a public meeting in Gogamukh where leaders of AASU, AJYCP, TMPK and others calling for unified action against the construction of the mega dam on Subansiri.
A delegation of various organizations and students bodies visited the LSHEP site at Gerukamukh on Monday.
The National Hydro Electrical Power Corporation (NHPC), which is constructing the dam, showed the visiting organizations the latest state of the site.
An official from NHPC said that latest natural phenomenon was quite normal to the design of the mega structure.
He explained that as per planning, construction period of LSHEP was considered for seven months during non-monsoon period from October to April.
“Upstream coffer dam 31m high at 100m upstream of dam axis and downstream coffer dam 21m at 100m downstream are constructed to divert the river water through diversion tunnels to facilitate dam construction during non-monsoon period,” the official told this correspondent.
The official further said that the diversion scheme was designed to cater for non-monsoon floods while coffer dams were expected to get damaged during monsoon flood from May to September and as such, required rebuilding before undertaking work in subsequent working seasons.
The main dam was constructed more than 30m above bed level, the upstream coffer dam was no more required to divert the river through diversion tunnels.
Downstream coffer dam is required to stop the backflow of the river coming out of the diversion tunnel to the spillway area during non-monsoon months.
“As such washing away of coffer dam during monsoon period is a usual event for the LSHEP,” said the officer.
On overflowing of river above the dam the NHPC official said that as per planning from the economic consideration, the diversion tunnels were designed to divert river water up to 4550 cum/sec which is 1 in 25 years non-monsoon flood of 7 months from October to April.
During monsoon period, whenever flow of water is more than 4550 cum/sec, excess water will flow over the dam during construction period.
“So during construction period, overflowing of water during monsoon period every year is normal occurrence,” explained the official.