The Bhutanese Leading the way.
Just before the visit of Prime Minister Narendra Modi, the Punatsangchu Hydroelectric Project Authority (PHPA) for the 1,200 MW P-I project had a meeting that green lighted stabilization measures on the right bank proposed by joint experts from both countries.
As a part of this, an Indian team of experts from Central Water Commission (CWC) and Central Electricity Authority (CEA), who are also the project consultants, along with Bhutanese experts are at the P I site doing a detailed joint survey.
They will sit with the contractor and design the final stabilization measures.
An official from the Ministry of Energy and Natural Resources (MoENR) said, “Over the last couple of years, the GoI and RGoB experts met and deliberated extensively on the long-term stabilization measures for the P-I dam’s right bank hill slope. The measures to be implemented were eventually agreed to and firmed up sometime in the middle of 2025. The proposed measures were thereafter endorsed by the two governments, and based on this, it was decided to resume construction of the dam.”
The official said the PHPA-I Authority decided that CWC shall, with engagement of Bhutanese counterparts, undertake detailed design of the stabilization measures as endorsed by GoI and RGoB.
The stabilization measures comprise mainly of RCC piles and cable anchors. RCC piles are giant concrete pillars that will be driven into the right bank to pin the unstable upper areas into deeper hard rock. The diameter of the RCC piles can be around 2 meters.
Hundreds of RCC piles will be used on the right bank. Past proposals were on using 265 such RCC piles under three sections of the right bank of the dam instead of excavating more due to the weakness there, but the latest proposal on this is not known or finalized yet.
Cable anchors are metal bolts or rods that will be drilled into the right bank to again pin the unstable rocks and stich things together.
Apart from these, the main focus will be on the removal of the overburden uphill of the National Highway at 26 degrees covering 150 meters upstream to 300 meters downstream of the dam.
This means 450 meters of overburden length above the dam area on the right bank will see massive excavation to reduce the size and pressure of the right bank. This is expected to affect even the current PHPA colony. The excavation will be done at a steeper 26 degrees.
The Indian side had wanted to do a shallower 30 degrees cut which would mean removing less overburden, but the Bhutanese side wanted more overburden removed for long-term safety at 26 degrees and both sides were stuck for a long time on this. There was movement only when Bhutan offered to pay the additional Nu 4 billion for the additional overburden removal.
The remedial measures also include installation of deep drainage wells on the right bank. This is to let the water out naturally of the right bank, especially for the future when the dam gets filled and the right bank gets charged with water.
An additional measure is strengthening and leaving one of the diversion tunnels for use as a spillway during the operation stage.
Currently, there are two diversion tunnels which are diverting the Punatsangchu river away from the dam area. Normally, once the dam is built, both these tunnels would be permanently blocked. Here, the proposal is to retain one tunnel after strengthening it and putting a gate over it so that it can be used as an additional sluice gate to let water out when needed.
The official said that presently, the design teams from GoI and RGoB counterparts are at the project site and carrying out detailed site assessments to enable the designing of the stabilization measures, especially the offloading of the right bank slope.
In terms of the timeline and budget for the stabilization measures, the official said it will be based on the design and the complexities under assessment at the moment. This will be finalized together in close consultation and coordination by the project with the designers, consultants, experts and the contractors.
