The Brahmaputra, a trans-boundary river flows within the Brahmaputra Sub-basin, which is part of the Ganga-Brahmaputra basin. Both the rivers discharge into the Bay of Bengal. The Brahmaputra and its major tributaries have a catchment area of 580000 sq. km according to a World Bank report. About 50% of the basin lies within the Chinese territory and 33.6 % lies within the Indian territory. The rest lies in Bhutan and Bangladesh. There are over eight sub-sub basins within Indian, Bhutan territories contributing a significant amount of water to the river. The surface run-off in the Brahmaputra varies from 3,244 m3/s in March (mostly due o glacial melt) to 44,752 m3 /s in July (due to the Indian Monsoon). The rain-fall within these eight sub-basins varies from 1000 to 4000 mm/year while the tributaries of Tsangpo River (Yarlung Zangbo, River Brahmaputra as it is known in Tibet), lying within the Tibetan plateau receives an annual rain-fall about 100-400 mm/y. The surface run-off in Tsangpo River is due to glacial melt that happens mostly during the April-May months. The Lunpo Gangri, Nyainqentanglha Feng, Bairiga, Gyala Peri, and Namcha Barwa are the glaciers supplying water to Yarlung Zangbo River. The Yalung Zangbo river, originating in Lunpo Gangri glacier in NW Tibetan Plateau, flows in an easterly direction for about 1625 km before taking a southerly bend at ( Shuomatan Point ) NE part of Arunachal Pradesh and is joined by the eight tributaries before discharging into the Bay of Bengal. So, the major run-off in the Brahmaputra is due to the eight tributaries located within India, Bhutan, Nepal, and not in Tibet. Further, most of the time the water in Yalung Zangpo is frozen and the flow is only during summer-glacial melt time. The best example to understand this phenomenon is the Stakna dam in Leh, Ladakh. This dam generates 2 MW only for two to three months in a year. China has already constructed Zangmu Dam (hydroelectric) with a generation capacity of 510 MWe in 2010 that is operational now.
China is planning to construct another dam north of Arunachal Pradesh where the Yarlung Zangbo river flows in a gorge known as Yarlung Zangbo Grand Canyon in Medog country.
The run-off in Yarlung Zangbo River is much less compared to the run-off in the Brahmaputra due to heavy rainfall in the eight sub-basins in Bhutan, and India. The Medog County dam is not a real threat to India as the water flows only in the summer months. India can construct several dams in Arunachal Pradesh and contain frequent floods in Assam. Such dams can control any unexpected flow into the Brahmaputra from the proposed dam in Medog County. It is not clear why India is not in a mood to construct any dam over the Brahmaputra in Arunachal Pradesh. If this is political then no one expects the ruling party (s) will know.
China will think twice before building a large dam across Yarlung Zangbo river in Yarlung Zangbo Grand Canyon in Medog country. In 1950 Medog experienced 8.6 M earthquake ( Assam-Tibet earthquake, 15 August 1950, 14.09 UTC; it is Medog earthquake) that killed more than 800 people in Qamdo Zhamo area. The village Yedong slid into the river Yarlung Zangbo and was washed away. According to the USGS report, the causality was much higher than anticipated. Data on the causality in Medog was not released by China. This earthquake has changed the topography of the region due to several major landslides. Numerous aftershocks of magnitude 6 were recorded. Based on historical earthquake data research has predicted another major event in Medog in the near future.
As rightly predicted, Medog county experienced 6.3 M earthquake on 24 April 2019 at 4.15 (Beijing time). This region is prone to large earthquakes due to the natural tectonic setting. The Indian plate is going below the Eurasian plate causing crustal shortening (region of fault). This region is under constant stress due to two plates hitting each other (converging-in scientific terms, due to Subduction). This is a shallow earthquake with the epicentre located at a depth of 13.3 km due to rupture (sudden slip). Constructing a dam over this region will make this region more vulnerable to earthquakes due to reservoir induced seismicity. In layman’s language, when a dam is constructed over such a region, the water impounded by the dam creates enormous pressure on the fault and the water seeping into the fault plane acts as a lubricant releasing the friction between the two plates causing a sudden slip. The region on the Chinese side is more prone to major damage than Assam or Arunachal Pradesh. So China will think twice before impounding a huge volume of water in the dam if at all it constructs one in Medog County. Scientific analysis is different from political for Yarlung Zangbo.
Views expressed above are the author’s own.
Views expressed above are the author’s own.
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