File image of the Brahmaputra

It took more than two weeks for Assam Chief Minister Sarbananda Sonowal to confirm that New Delhi had taken up the puzzling issue of contamination of Brahmaputra water with Beijing.

Sonowal’s announcement came after he met Prime Minister Narendra Modi and the External Affairs Minister Sushma Swaraj on Wednesday evening.

For more than two weeks, people on both the banks of the mighty river in Assam and Arunachal Pradesh are perplexed and worried. The river water turned black and turbid along its entire course. And, till now, there is no scientific explanation for the cause of pollution of one of the largest river systems of the world.

The “worry” multiplied after the Arunachal Pradesh State Water Quality Testing Laboratory said in its reports that the water of the Siang river was “totally unfit” for human consumption. A high turbidity level of more than 425 Nephelometric Turbidity Unit (NTU) was reported by the lab. The iron content was recorded at 1.65 mg/litre, which was much higher than the permissible limits.

The Brahmaputra originates in Tibet where it is called Yarlung Tsangpo and is known as Siang in Arunachal Pradesh before it enters Assam and flows southwards to the sea through Bangladesh. Two other rivers – Lohit and Dibang in Arunachal Pradesh are also tributaries of the Brahmaputra.

Water samples were collected from 15 locations from Jonai to Dhubri in Assam and have been sent to the Indian Institute of Chemical Technology (IICT), Hyderabad and IIT Guwahati for tests. Both the institutions are yet to make any statement on the time to be taken to undertake the tests. The government will probably decide on the next course of action only after the reports from the labs.

While “worry” of the common people remained unaddressed for more than two weeks, opposition political parties shamelessly were seen busy politicizing the issue. Former Assam Chief Minister Tarun Gogoi said that Brahmaputra River was considered the lifeline of Assam and threatened to launch ‘save Brahmaputra, save Assam’ agitation.

China has blatantly denied its river systems flowing into India and cautioned that India should not conduct unfounded speculation and reports on the issue. It is unfortunate that our government is yet to counter Beijing’s claim on the high level of turbidity of the river water.

What may have happened?

Initial reports claimed China was building a dam on the upstream of the river system and the high level of turbidity was due to massive use of cement and other construction materials. The second claim in the media was that the China was making a tunnel to divert water from the river to the Taklamakan desert in the Xinjiang province. But, Beijing has absolutely denied both the allegations.

The third theory, which was put forward by some geologists, claimed the recent earthquake in Tibet was the most probable cause of the muddy water flowing through the Brahmaputra. A strong 6.9 magnitude earthquake in Linzhi in the Tibet Autonomous Region had shaken the entire area. After few days of the earthquake, there was a sharp change in the colour of the water, which was first noticed at Gelling and Tuting in the Upper Siang district in Arunachal Pradesh.

Some even claimed China’s thirst to exploit the rich deposits in the Tibetan plateau has spread environmental pollution, and ultimately led to the condition of high turbidity of the Brahmaputra river system.

All the four theories on the possible cause of the contamination of Siang river further complicated the issue. Assam Chief Minister Sarbananda Sonowal is also under tremendous pressure to persuade New Delhi to exert diplomatic pressure on Beijing to immediately assess the cause of the problem and find an instant resolution method.

Most possible cause

One Indian expert, who has been closely studying the subject, told this writer that there could be another possible cause of the contamination of Siang – release of the silt-excluders of the Zangmu Dam in the river system. So far, no one spoke about the possibility.

The 510 MW Zangmu Dam is a gravity dam on the Yarlung Zangbo (Brahmaputra river system), and is about 9 km northwest of Gyaca in Tibet. The dam is very close to the Bhutan-India border. Stage I of the project was commissioned in November 2014 and the project was completed in October 2015.

The expert said though China claims it to be a run-of-the-river project, the Zangmu Dam is a big dam, and is 381 ft in height. The dam’s reservoir has a daily active pondage of about 8, 66, 00,000 m3 and normal reservoir elevation of 3,310 m (10,860 ft). On its right bank is the spillway, plunge pool and bottom outlet (for silt).

During the last three years of commissioning of State I of the project, there may have been massive siltation in the reservoir, the expert said. Generally, there is more siltation in hydro-reservoirs in the fragile eastern Himalayas.

According to the expert, if silt is not cleared for two to three years, there is heavy siltation in the reservoir (closer to the sluice gates) and affects the generation capacity of the projects. Moreover, pH of the water also goes high, and is not good for the steel and concrete structures.

After deposition for a long time, the silt in the hydro reservoir is fine grains, and is more like clay. And if released during the lean season, the water will suddenly turn muddy and opaque. It may also result in higher NTU level of the water, the expert said.

The silt-excluders, which clear the silt from reservoirs, are placed below the sluice gates and huge amount of silt it flushed out every minute once the under-water doors are opened. So far, the Indian experts don’t have details of the siltation rate in Zangmu Dam in South Tibet, nor do they have any details of how much silt may have been released during the last two weeks.

Experts are of the opinion that it could be a deliberate attempt by China to suddenly open the silt excluders. There are more reasons to worry because China has reportedly three more dams on the river — the Dagu (640 MW) and Jiexu (560 MW) dams will be constructed upstream of Zangmu, while the Jiacha Dam (320 MW) downstream.

In absence of a riparian right, it will be interesting to see how India will handle China on the Brahmaputra issue.

The writer is Editor-in-chief of www.nenow.inand can be reached at  

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Anirban Roy

Anirban Roy is Editor-in-Chief of Northeast Now. He can be reached at:

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  1. The expert’s name could have been shared if he is not from intelligence sources to add more credibility to the fourth possibility which to me sounds more plausible.. Great piece.. Lots of insight without playing on the nationalistic fervor..

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