A satellite image taken on December 10 shows how the colour of river water changes as the Brahmaputra, flowing northward in Tibet, crosses the landslide zone. A satellite image taken on December 10 shows how the colour of river water changes as the Brahmaputra, flowing northward in Tibet, crosses the landslide zone.

Massive landslides caused by a series of earthquakes in Tibet is darkening the Brahmaputra waters, satellite images show, and not Chinese construction activity as raised by a BJD MP in Lok Sabha.

The accumulating debris has caused partial blockages at three locations, forming natural dams on 6 km of the river across a 12-km stretch in China. The worry for India is that these three dams may merge and eventually give away to result in a deluge downstream.

Lab tests have established that the water has darkened due to turbidity typically caused by landslides. “There is no foul play involved. However, landslide-induced turbidity usually subsides within a week. So we are examining the situation through satellite images as the affected area is not within our territory. We will get a clearer picture soon,” Pradeep Kumar, member (river management), Central Water Commission, told The Indian Express.

A preliminary study by two researchers from Bengaluru-based National Centre for Biological Sciences (NCBS) and Ashoka Trust for Research in Ecology and the Environment (ATREE) shows that quake-induced landslides on the river continued for over three weeks, which probably explains the prolonged turbidity.

An area spanning approximately 100 sq km was devastated by massive landslides after a 6.4 magnitude earthquake struck below the Gyala Peri peak in Tibet on November 17, which was followed by six 4-plus magnitude earthquakes within a radius of 40 km over the next seven days.

Map shows site of quake. Map shows site of quake.

On Tuesday, Bhartruhari Mahtab, BJD MP from Cuttack, raised the issue of the contamination of the Brahmaputra river water during Zero Hour in the Lok Sabha. Later, speaking to The Indian Express, he said, “The contamination may have been caused due to the construction of a dam by China on a tributary of the Brahmaputra. We are a riparian country and China is obliged to share all hydro-meteorological data with us. If it does not do so, we should raise the matter at all international fora.”

On December 13, Assam Chief Minister Sarbananda Sonowal’s office said he had met Prime Minister Narendra Modi in New Delhi on the blackening of the Brahmaputra’s waters, and that External Affairs Minister Sushma Swaraj had informed that her ministry had started an exhaustive study after contacting authorities in China.

The Yarlung-Tsangpo river cuts through the world’s tallest gorge between Gyala Peri and Namcha Barwa before merging with the Yigong-Tsangpo river and taking a 180-degree turn southward to flow into Arunachal Pradesh where it is known as Siang. Further downstream, major tributaries — such as the Lohit and Dibang — join the Siang to make it the Brahmaputra.

A satellite image taken on December 10 shows how the colour of river water changes as the Brahmaputra, flowing northward in Tibet, crosses the landslide zone. CLICK to enlarge A satellite image taken on December 10 shows how the colour of river water changes as the Brahmaputra, flowing northward in Tibet, crosses the landslide zone. CLICK to enlarge

The study by Chintan Sheth (NCBS) and Anirban Datta-Roy (ATREE) reported that images captured by the European Space Agency’s Sentinel-2 satellite on December 10 captured the landslide in progress as well as blockages of the Yarlung-Tsangpo river by debris at three locations in the Bayi district, Nyingchi County. The evidence puts to rest fears that dam construction and tunnelling work upstream the Yarlung-Tsangpo in China were responsible for the darkening of Brahmaputra waters.

“Three natural dams have formed one behind the other. While the dams are significantly smaller than the Yigong dam, which led to catastrophic flooding of the Brahmaputra in 2000, it is too early to rule out the possibility of these three dams merging and becoming larger. Blockage of river flow by debris is unpredictable as the area is extremely unstable and possibly still disposing rocks,” the report said.

In April 2000, a massive landslide on the Yigong-Tsangpo blocked the river and created a 90-metre deep natural reservoir across 2.5 square kilometres. This natural dam gave way in June, flooding areas as far as 400 km downstream, sweeping away large swathes of forest, and destroying over 50 villages in Arunachal Pradesh and Assam.

Claiming that the present landslide was perhaps the largest estimated in 2017 and “catastrophically larger than the one in 2000,” the study underlined the urgency for real-time aerial monitoring to keep track of how the dams are evolving, and to prepare for any eventuality. In 2000, China had failed to warn India about the natural dam formation and its potential consequences.

“It is likely that natural dams have formed due to landslides after the earthquake. We monitor all natural lakes in the region. China shares river data with us. We have already sought help from the National Remote Sensing Centre and will do whatever is necessary when we have a clearer picture,” said CWC’s Kumar.

On December 4, Union Minister of State for Water Resources Arjun Ram Meghwal referred to preliminary findings, which indicated that the path of the river was temporarily obstructed after an earthquake in Tibet on November 17. “The Central Water Commission has started looking into the matter,” he said.

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