PHPA proposes new dam location

Thimphu: In what may be a major change to the 1095 MW Punatsangchu I project, the Punatsangchu hydroelectricity project authority (PHPA) has proposed a new dam location, that will be stabler and generate more power.

According to PHPA, the new dam will increase generation by 75-200 MW. However, the downside is that 70 acres of paddy cropland, along with some houses will be submerged, 50 acres more than the present location.

“The current location of the dam means that we’d have to do 73 m of digging below the river bed to reach its hard rock area,” said a PHPA technician. “This could be a potential problem because digging will be up to a certain level, after which cement will be injected into the soil and a concrete layer put on it, which is not as stable as a hard rock bed,” said another official.

The current location will also mean that a lot of water pressure would be falling on the hillsides where excavations would be needed. With an additional 63 m above the riverbed, the total height would come to 137 m.

The new location is supposed to have an easy to reach hard rock bed and will require only around 30 m of digging for establishing the dam foundation.

This new site was discovered when Road Rim studies on the stability of the road along the project were being carried out.

The new dam location is around 7.1 km downstream from the Wangdue Bridge, compared to the current location of 8.5 km.

“Even if we take the minimum extra generation capacity of 75 MW, the government can expect around Nu 700 million in additional annual revenue,” said a PHPA official. Generation could go up from 1095 MW to around 1170 MW plus. The additional power will only require half the normal cost of construction.

“The 60 MW Kurichu itself cost around Nu 5.6 billion but this 75-200 MW additional electricity is expected to cost only an additional Nu 1.2 billion on the total project cost of around Nu 35.148 billion,” said a PHPA official.

This additional power is expected to be generated by an increase in the length of the water tunnel, with more water force hitting the six turbines downstream below the pressure shaft.

This is the third improvement on the dam, with an earlier Norwegian and Japanese study estimating only 870 MW at 10 km downstream. The main survey showing 1095 MW capacity at 8.5 km downstream was done by WAPCOS.

Under the first study, only 7.5 acres of paddy land was being submerged, 20 acres under the WAPCOS study and now 70 acres of cultivable land, along with a few houses, in the latest study.

PHPA officials said that, in the eventuality of relocation, around Nu 100 million had been set aside to compensate those who may lose any property under the latest proposal.

It has also been learnt that Bhutanese contractors will be handed over the entire project of building roads and residential and office buildings worth Nu 1.8 billion for the project and cement for the entire project worth Nu 2.1 billion will be taken from Penden Cement.

On the current work being carried out PHPA, managing director Mr R N Khazanchi said, “Of the 3 bridges (40 tonnes capacity each) required, we’ve already received one heading to the power station and are in the process of installing it.” Bridges are vital since the entire project falls across the river and the Wangdue-Tsirang highway and the remaining two bridges will head for the dam and the head race tunnel and are expected shortly. “PHPA staff have already found rented accommodation and are carrying out preliminary optimization work to prepare for construction and power lines needed for feeding the project are also 75% complete,” he added.

Access roads are also being built to the various project sites.

The project is divided into three main components of dam building, tunnel boring and power plant building. The dam is expected to take the longest time, 7 years, and be the most expensive among the lot. The other two works will also start at the same time.