P-1 dam site

Barrage option means Nu 4.85 bn in stabilization works and chunk of Nu 23 bn in dam works is a waste

With the current Punatsangchu I dam site is likely to be abandoned with a barrage upstream being proposed by a third party foreign expert, it raises a question over the tremendous wastage in works and funds at the current dam site.

Since the start of the construction of the project, of the Nu 80 bn spent so far on P-1 project till date Nu 23 bn has been spent on the dam site which involves digging the foundation of the dam, construction of a small part of the dam and construction of tunnels and de-silting chambers.

Of the around Nu 23 bn a little more than half the amount worth of construction can be reused for the barrage but a sizeable chunk will go to waste. The part that can be reused for a barrage is the 4 large de-silting chamber and around 11 km of tunnels.

Another Nu 4.5 bn has been spent since 2013 on the right bank when the first slide happened in stabilization and strengthening measures but it has failed to prevent the movement in the right bank with slides again in August 2016 and in January 2019.

Given the various studies and the long term impact the Bhutanese side is in favour of a barrage over the dam and the Druk Green Power Corporation (DGPC) is already doing studies for the barrage.

However, the Indian side is yet to get back to the new and recent proposal of abandoning the current unstable dam site and going for the barrage. The Bhutanese side is pushing for an authority meeting soon to discuss and finalize this with the Indian side.

Complicating the picture and a new twist is the fact that two Indian consultants which are the Central Water Commission (CWC) and National Hydro Power Corporation (NHPC) who had initially disagreed on the safety of the right bank and the current dam site are now on the same page indicating it is safe to build the dam at the current site.

The Bhutanese side is not convinced given the differing data only until recently and also a validation by a foreign third party that the current site is not safe or stable enough for a dam and so a barrage upstream is recommended instead.

Following the 2019 January slide the CWC which is the civil works consultant for P-1 was asked to come up with a comprehensive solution. It gave its reports and solution by October and December 2019 recommending extensive strengthening works on the current site saying that the right bank is safe enough to build the dam.

A dam site would have to have a minimum factor of safety of 1 or above as per international standards while the European factor of safety is 1.5 to 1.8.

The CWC in its report and drawings gave a factor of safety of 1.2 to 1.4 for the site.

The Bhutanese side was not fully convinced with the review of the CWC and the strengthening measures and so it asked another Indian government company NHPC to do a review if the CWC proposal.

The NHPC in mid 2020 presented its review of the CWC report as a third party and disagreed with the CWC assessment and said the factor of safety is below 1 and hence it is not safe enough to build a dam.

The NHPC was saying that CWC’s strengthening measures and drawings for the right bank presented to the Technical Coordination Committee in October and December 2019 is not secure enough for a dam to be built right next to it.

The NHPC instead recommended to build a smaller structure in the form of a barrage 820 meters upstream of the current site.

The project authority asked to two companies with different findings to reconcile their contradictory findings. The two companies have now come back giving a factor of safety of 1.4.

However, this calls into question how the NHPC drastically changed its own stance and data to fit in with the CWC.

The government through DGPC had hired a foreign company to do a review of the review which also showed the current site to be unsafe with a recommendation for a barrage.

The source of the current mess and wastage goes back to 2008 when the dam site was changed and in 2009 when the overall consultant WAPCOS and the civil consultant CWC tendered the dam site despite a study showing weaknesses.

An official said that part of the problem was the CWC had followed the river valley guidelines of India while doing the tests for the new dam site which had missed out how serious the right bank problem really was.

To avoid this in the future the Bhutanese side in 2009 came out with more detailed guidelines that all detailed project reports must use which calls for more detailed testing.


The problem all started in 2008 when the then PHPA MD R.N Khazanchi proposed to change the original dam site to generate more power. The then cabinet agreed in June 2008 based on Khazanchi’s presentation.

A Joint Audit Report of the Royal Audit Authority (RAA) of Bhutan and the Comptroller General Audit of India (CAG) of 2012-13 said that the PHPA, its main consultant WAPCOS and CWC knew that there were geological weaknesses at the right bank area but still went ahead with the tendering of the dam on the same site in 2009.

A geo technical appraisal report prepared by the Geological Survey of India (GSI) identified some weak geological features and said that additional investigations were required for the exact delineation of the weak geological features.

However, instead of conducting further investigations PHPA’s consultant WAPCOS, on behalf of GSI, issued a clearance for the project dam bids to be opened on 16th February 2009.

The problem made itself known with a major slide on the right bank in July 2013 which at the time the overall consultant WAPCOS and the civil consultant CWC said could be fixed with Nu 3.5 bn of mitigation measures. However, despite the measures another major slide happened in August 2016 and again despite additional mitigation measures the same area slid on 22nd January 2019.

After this, the government in the 21st PHPA Authority meeting in January 2019 insisted to the Indian consultants to come up with a comprehensive solution.

CWC was tasked to come up with a holistic solution to strengthen the Right Bank without which construction of the Dam on the right bank side could not proceed.  The report was submitted by CWC on 1st October 2019 and detailed drawings later in December of the same year.

PHPA officials at the time said they were confident enough with the report to start concreting of the dam from the stable left bank side.

One suggestion of the CWC was that the dam on the right bank side be constructed over 288 concrete piles driven into the ground to avoid excavating the shear zone below the right bank side

The Bhutanese side not very convinced with the idea of concrete piles under the dam for the long term and feeling the need for an overall review of CWC’s proposal called for a review in the Technical Coordination Committee meeting

The National Hydro Power Corporation (NHPC) was then called upon to do a third party review of the WAPCOS and CWC proposal.

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