Lower Subansiri Hydro Electric Project: A doom in the downstream

For a population living downstream of a dam that has its design and location always mired in controversies with many claiming it to be flawed, the news of flood and landslide severely affecting the site and structure brings in a twin feeling of dread and despair. And when the dam is the biggest hydropower project now being built in India, phrases like “apocalypse” or “nightmare” invariably come to one’s mind.

Dangers from Lower Subansiri Hydroelectric Power Project

The Lower Subansiri Hydroelectric Power Project’s fragility can be understood by the fact that, within a few months of rain, the project — which was scheduled for commissioning soon after many delays — is severely damaged by gushing water and landslides. There are rising concerns that the river may alter its natural path causing devastating consequences downstream.

“Due to extensive rains for the last two-three months in the upper stretch of the project in Arunachal Pradesh, the hill linked to the main dam in Assam is witnessing massive landslides. The diversion tunnel is closed resulting in the overflow of the excess water over the main dam. The force of the water is such that the guard wall protecting the under-construction powerhouse is severely damaged and the powerhouse itself is under water. Needless to say that if the main dam collapses someday it will be a catastrophe downstream,” says water resources engineer Pradip Pujari.

Implemented by the state-run National Hydro Electric Power Corporation Ltd, the Lower Subansiri Hydroelectric Power Project is the biggest hydroelectric project undertaken in India so far and is a run-of-river scheme on river Subansiri located partly in the Dhemaji district of Assam and Subansiri district of Arunachal Pradesh.

According to Climate Technology Centre and Network, the “run-of-river hydro projects use the natural downward flow of rivers and micro turbine generators to capture the kinetic energy carried by water. Typically, water is taken from the river at a high point and diverted to a channel, pipeline, or pressurised pipeline (or penstock). The technology is applied best where there is a considerably fast moving river with steady seasonal water. How much electrical energy can be generated by a hydroelectric turbine depends on the flow/quantity of water, and the height from which it has fallen (the head). The higher the head, and the larger the flow, the more electricity can be generated”.

In other words, “‘run-of-river plant’ means a hydro-electric plant that develops power without Live Storage as an integral part of the plant, except for Pondage and Surcharge Storage”.

The Lower Subansiri HEP consists of one Concrete Gravity Dam of 116-metre high above the river bed level and 123-metre high above the deepest foundation level. It has a surface powerhouse with an installed capacity of 2,000 MW with eight units of 250 MW capacity turbines each. The project received its environment clearance through Letter No. J-12011/40/2001-IA-I dated 16 July 2003 and the construction work on the project began in January 2005.

Barrage of technical issues in Lower Subansiri Hydroelectric Project

The location of the project as stated on the official website, with no specific indication of the dam site and rather ambiguous facts provided, exposes the insincerity of NHPC. There is no mention of Gerukamukh, the project site, at all, at least at first sight. The project has remained controversial from the start, with numerous experts and panels pointing out significant problems in its structure and design.

In the 44th meeting of the Expert Appraisal Committee on River Valley and Hydro Electric Projects constituted under the provisions of EIA Notification 2006 which was held on 11 December, 2010 in New Delhi, the safety and stability aspect of the Lower Subansiri HEP dam came under deep scrutiny.

“The site specific seismic design parameter for peak ground acceleration (pga) value of 0.38g considered by NHPC is inadequate as the whole of the North East falls under Zone V — (very high damage risk zone) with probability of earthquakes of MSK IX or more. Previously the earthquakes of 8.7 (Shillong earthquake) and 8.5 (Assam earthquake) on the Richter scale have been experienced. In view of this, the design parameters need to be reconsidered to be at least 8.5 M at pga of 0.5g. The broad scale data provided by NHPC is shockingly lacking and there are gaps in the data. A mega earthquake of 1947 has not been reported. Therefore, lithologically and seismologically it needs deeper investigation, not only for lower but upper Subansiri too. A cumulative effect study should be conducted,” the minutes of the meeting noted.

The Lower Subansiri Project was originally conceptualised by the Brahmaputra Board as a flood mitigation project and the production of hydroelectricity was a secondary element of it.

“The Brahmaputra Board also submitted a detailed project report with the government recommending an Earth and Rock-fill Dam given the geological assessment of the site. However, the Centre ultimately bowed to the immense pressure from the Arunachal Pradesh government which also shares part of the project and finally approved it as a hydroelectric project and not as a flood protection structure in 1999. NHPC was entrusted with the responsibility of building it,” says Pujari.

The project was then divided into three parts — Subansiri Upper, Subansiri Middle and Subansiri Lower.

The construction began in 2005 but lack of clarity over the downstream impact soon led to massive protests in Assam which grew bigger after the Assam Expert Group formed under the aegis of the All Assam Students’ Union and the Assam government in 2008 submitted a report in 2011 objecting to the site selection due to geological reasons and the adverse impact that the project might cause downstream. The project finally came to a standstill in December 2011. Different committees were formed in between and none came on the same page ever and some real movement happened only after the BJP came to power at the Centre in 2014.

Although differences still existed between Central and state experts, the work on the dam resumed in October 2019 with NHPC expressing willingness to make necessary changes albeit partially keeping the safety scenario in mind. However, the recent rains and the impact that they had on the dam have raised serious doubts about the safety quotient of the project.

Is NHPC making a waterbomb?

Practising engineer and senior technical consultant at Srishtie, JN Khataniar feels that the recent happenings at the country’s biggest hydropower project at Lower Subansiri are not at all unexpected.

“This was bound to happen as the NHPC disregarded scientific approaches for the project from the beginning. Moreover, there were negligences from many stakeholders attached to the project,” says Khataniar.

“This is the result of past mistakes which are getting reflected right now. The project was given to NHPC on a turkey basis. So they had the upper hand to investigate, plan, design and execute the project. Many committees gave many recommendations but no one took any accountability for those ensuring that their recommendations if implemented will make the dam foolproof. All we need is a foolproof dam. We need hydroelectric projects. NHPC will also need hydroelectric projects but it should be foolproof,” says the senior technical consultant.

“All they did was to take a trial-and-error approach. All they are doing now is strengthening the project or else why will it take such a long time to execute the project? They have widened the dam but ultimately the recent collapses indicate that the dam is not foolproof. In all practicality, the Lower Subansiri Hydro Electric Project is not scientific,” says Khataniar.

Issues with the dam have been never ending with more problems than solutions. The lackadaisical attitude of the NHPC might even lead to depleting faith in hydropower projects as a source of energy. The effectiveness of numerous recommendations that came from many committees is also questionable as the project does not seem safe enough as the experts whose recommendations are implemented claimed it would be.

“The project was originally conceptualised as a three-stage integrated online power project on the same river Subansiri. The upper stage dam was supposed to have 10 metres and the middle stage dam, 15 metres of flood cushioning and zero metres for the lower stage of the Subansiri dam. The 10 metres and 15 metres of flood cushioning is possible without any adverse impact on the ongoing project site. However, in the absence of upper and middle-stage projects, the river flow is putting enormous pressure on the 116 metres-high main dam,” says Khataniar.

Are there any remedies to prevent a catastrophe?

Citizens in upper Assam particularly in the districts of Lakhimpur and Majuli in Assam, who live downstream of the NEEPCO-managed 405 MW Ranganadi Hydroelectric Power Project, are already bearing the brunt of ravaging floods leading to increased loss of life and property every year. As soon as the sluice gates are opened to protect the Ranganadi dam at Yazali in Arunachal Pradesh, the fury of water causes mayhem in downstream Assam. It is unlikely that people who are now facing the wrath of a 2,000 MW project will be convinced any further by NHPC’s callous attitude. In the great march to make India a hydropower giant, innocent citizens downstream and closer to the project areas have become nothing more than expendables.

Ironically, the fierce protests that even forced NHPC to stop work on the project for years have now stymied. People’s belief in the protests and the leaders who led them with the hope that the project’s faults will be rectified or else they won’t let the project happen has dipped to near non-existent levels.

“The people no longer trust the leading figures of the anti-dam protests as they have become subdued and silent due to mysterious reasons even when the dam work resumed full swing despite many unanswered questions. A section of the media was also misled by the NHPC,” says Pujari.

“Over 80 per cent of the project work is complete now and suddenly the so-called leaders waking up from their slumber won’t halt a project of this magnitude. There will be delays but no abandonment. Our so-called leaders even failed to extract the maximum out of the project and now it is simply too late for anything,” he says.

The Lower Subansiri Project, which was originally estimated to be a Rs 6,285 crore project, has seen the highest cost overrun in the country with the figure going steeply north by more than triple at Rs 13,211 crore. The project cost is now estimated to be Rs 19,496 which in all likelihood will go up after the recent developments.

The leading figures of anti-dam protests including Raijor Dal supremo and Sivasagar MLA Akhil Gogoi failed to ask for more free power quota and facilities from the project equivalent to what Arunachal Pradesh is extracting from the project.

The only thing now left is to ensure the safety of the people and property downstream in whatever way possible.

“The best we can do is to make a very strong demand for measures to protect the people downstream. People are already sceptical about NHPC and any measure they announce won’t convince the people of their safety downstream. I think both the Centre and the Assam government should immediately appoint an expert committee to find out what triggered the recent landslides in Gerukamukh near the main dam,” says Pujari.

It is high time for the Assam government to act on a war footing and not remain oblivious to the crisis at the dam site.

“A Joint Steering Committee as per the recommendation from the Assam government and approval by the Centre was constituted and it created a Rs 470 crore scheme for the safety and development of the downstream area. In 2014, the Governor of Assam formed a Core Group of Assam with senior state government officials to oversee the implementation of the scheme. The Assam government should check how this committee is performing its duties because people downstream are hardly convinced. In addition, mandatory project insurance for those living near the dam site and the probable affected areas downstream must be ensured by NHPC as it is highly unlikely that the project will be shelved. Convincing NHPC to take these citizen-friendly steps seems to be the biggest task now,” says Pujari.

Whatever image the NHPC tries to project through its PR machinery for the outside world, in reality, the company knows quite well that they are caught in a situation where further mistakes may lead to wiping of places and people from the globe.

“The entire issue has to be tackled by NHPC Ltd very carefully with honesty and dedication without ignoring further technical aspects. The problem will have to be dealt with like an engineering challenge of the 21st century to achieve sheer perfection, and stability and to save the life and property of people downstream,” says Khataniar.

India’s biggest hydropower dam should be an engineering marvel and not a killer dam.

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