The Punatsangchhu-II hydroelectric project (PHPA II) dam site was filled with water and debris from the flooding between August 9 and 11 this year when the Punatsangchhu spilled over the cofferdam.
There are two cofferdams, 888m long and 12m diameters, one upstream of the campsite and another below it.
While many people, who watched the flooding on social media sites, were worried about the flooding, officials say that there is nothing to worry, as the cofferdam is designed for flooding.
Project officials said the dam height have reached varying heights, the tallest at about 20 meters.
PHPA II officials said work would resume once the water and debris that the flood deposited at its site is removed.
PHPA-II’s managing director, RN Khazanchi, said that it might take at least three months to clear the area.
But observers said that such flooding could be averted if there were more diversion tunnels. The 1,020-mega-watt project has only one diversion tunnel.
“This design is made considering the cost analysis between building more tunnels to divert the river so that the cofferdams don’t flood and letting the cofferdams flood,” a senior engineer said.
He said the engineers calculate at what stage of the dam construction the flooding could be. “So the work progress also takes place according to that timing. The flooding will not cause damage to the dam.”
Project officials said similar flooding occurred in June last year for about three days.
RN Khazanchi said the project studied the annual discharges over the past three decades. “The highest discharge of water was during the flood in 1994 with 2,500 cubic meters of water. We also took in the discharge during the peak seasons.”
The diversion tunnel has the capacity to divert 1,800 cubic metres of water.
The PHPA II dam will be 86m tall and 213.5m wide at the top. The intake structure near the dam is more than 80 percent complete, project officials said.
The revised project cost as of today remains at Nu 72.9 billion.
Work on the project started on December 17, 2010, with a completion schedule of seven years with fund from the government of India at 30 percent grant and 70 percent loan at the rate of 10 percent interest per annum starting from one year after the date of commercial operation.
The project is located on the right bank of Punatsangchhu along the Wangdue- Tsirang highway between 22km and 35km downstream of Wangdue bridge.