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Wed, 23 Jan 2019

Northeast Today

The Turbid Brahmaputra

The Turbid Brahmaputra
February 13
15:52 2018

January Edition, NET Bureau

The turbidity level in the Brahmaputra in Assam is much beyond the permissible limit for use as potable water. The river has turned muddy and the water has changed colour in the non-monsoon season, causing concern among the people and the authorities in Assam. Northeast Today reports

Siang to Brahmaputra

The Siang River in Arunachal Pradesh, the main tributary of the Yarlung Tsangpo (as the Brahmaputra is called in Tibet) began showing signs of turbidity in October, 2017, and two months later, the river began changing colour and gradually began turning visibly black. Arunachal’s Public Health Engineering Department, after testing a water sample of the river, confirmed the turbidity of the Siang’s waters to be several times higher than the permissible limit. Soon, reports of fish and animals dying from the polluted waters started to emerge from the Siang Valley. The Siang joins Lohit and Dibang rivers at Pashighat to form the Brahmaputra.

The muddiness that began emerging in Siang in the month of October, gradually began turning the Brahmaputra water muddy and the turbidity rate also began to increase. This forced the authorities in Assam to collect samples of Brahmaputra water at three places- Guwahati, Dibrugarh and Tezpur. And from tests carried out at District Level Laboratory of the Tezpur Division of the Public Health Engineering Department, it was confirmed that the water sample contained a lot of mineral properties.

Moreover, after carrying out tests on water samples (of Brahmaputra) collected on December 2, 2017, from four different locations- Bogibeel, Dibrugarh, Jonai and Pasighat- have confirmed high turbidity level. However, no traces of chemicals were found in the samples. The turbidity of the water sample collected from Bogibeel showed a turbidity of 400, even though the turbidity level of the water sample collected from the other three sites was much lower.

It may be mentioned here that the lab reports of the water sample collected at Siang on November 27, 2017, shows that Nephelometric Turbidity Unit (NTU) (the measure of turbidity) as 425 NTU- which is 400 times higher  than the permissible limit of 5 NTU for drinking water.

According to a report of study of environmental impact by the Arunachal Pradesh Pollution Control Board, Siang’s turbidity measure should have been between 12 and 15 NTU at this time of the year. Even in the monsoon season (September), Siang’s turbidity is between 295 and 329 NTU which, too, clears up after a short time.

Possible Causes

Various commentators have come with a number of explanations regarding the rise in turbidity in Brahmaputra water. From China constructing secret tunnel to divert Yarlung Tsangpo’s water to China constructing dam on the river to a series of earthquake triggering the massive flow of soil into the river.

Speaking to Northeast Today, Dr Bidyut Bikash Sarmah, a Guwahati-based environment researcher said, “I feel that there are many missing links and without the availability of certain crucial hydrological data, it would not be proper for anybody to draw any conclusion.”

“Based on my personal observations, I have the following hypothesis in this regard. The whole phenomenon is due to massive inflow of soil materials from mountains into the Yarlung-Tsangpo triggered by a series of earthquakes in the Nyingchi mountain ranges of China. According to USGS data, within a span of 9 days (November 15- November 23) a total of ten earthquakes shook the entire Nyingchi mountain ranges, which also includes the famous Namcha Bawra peak. Among all the earthquakes, the biggest measured M6.4 in magnitude. A M6.4 earthquake does not seem to be very big, but the main factor that might have played the role was the epicentre depth. This earthquake occurred at a depth of 8km only. In fact, except at two places, all other eight earthquakes occurred at depths of 10km. This simply means that, the whole mountain system, which has very steep slopes, received severe jolts. This may have resulted in earth avalanches in a single or multiple locations but all the soil materials flowed down to the river making it highly turbid,” he further added.

Assam Health Minister Himanta Biswa Sarma while interacting with the media on December 6 said that he suspects that the construction of a dam or some accident in China has caused the Brahmaputra’s water in the state to have abnormal deviations turning it muddy and containing cement particles.

Biswa Sarma’s suspicion cannot be ruled out as in 2016, China did make it public about its plans to build a dam on one of the tributaries of Yarlang Tsangpo. So, it is in fact possible that an accident might have collapsed some part of the dam and the broken particles might have intermixed with the river water and turned it turbid.

China, however, has declined these allegations and has clearly said that India should not point fingers towards China on every single occasion.

Final Words

Till the filing of this report, more water samples were being tested and the scientists were on a mission to find out the actual reason for this turbidity. Until the final report is made public, speculations must be kept at bay.


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