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The harnessing of Tibetan rivers influences drought/flood conditions in our border States

THE NEWS from across the Tibetan border about the Chinese building a barrage on the Sutlej river portends strategic concerns to the country's border areas. According to media reports, the Chinese have been constructing, for the past few years, a diversion structure across the Zada Gorge in the river (locally known as Lang Chen Khambab) located in the western part of Tibet and satellite imageries indicate the work as complete. So far, China does not appear to have taken India into confidence about this project which has the potential of controlling Sutlej flows into India. At present, except for a memorandum of understanding (MoU) for sharing the hydrological information of the Tibetan rivers concerned during flood season, there are no subsisting agreements between India and China on water related issues even though Indian rivers such as the Brahmaputra, Indus, Sutlej, Kosi, etc., originate from Tibet. As of now, Indian authorities do not appear to be much concerned about the possible upstream uses in Tibet to cause reduction in Himalayan river flows on the presumption that such utilisation will be minimal due to the terrain conditions and sparse population there. But if the Chinese plan is to divert the waters during lean periods in winter and release large flood flows during the glacier melting periods in summer, India has to be bothered about it as experienced in the recent past.

Flash floods

The flash floods which occurred in August 2000 when water levels in the Sutlej rose by about 30 m. in a short span of time at the Nathpa Jhakri Project (NJP) in Himachal Pradesh have raised many intriguing issues. The river discharge increased from 1,480 cumecs to 5,100 cumecs in two hours, leaving behind a trail of destruction in Himachal Pradesh. Luckily the Bhakra Reservoir downstream could absorb the floods thereby containing the devastation in the lower reaches in Punjab. Earlier, it was also seen that there was reduced inflow in the summer months into the Bhakra reservoir, an unusual feature during the snow-melting season.The floods could have been caused due to heavy rainfall in Tibet, or breaches in lakes upstream or due to collapse of constructed structures or failure of temporary obstructions across the river channel upstream.Interestingly, rainfall in the area is a rare event as most of the precipitation in the upper Sutlej is in the form of snowfall. Hence the flood could not have been caused by rainfall. The pre and post flood event satellite data did not show any noticeable change in the water spread in the connecting channel of the upper lakes (the Mansarovar and Rakas Tal) and hence breaches of the lakes contributing to these floods could also be ruled out. Hence it has to be concluded that the floods were triggered by the failure of a blockage across the river channel caused either due to construction activities or landslips. The reduced inflow into the Bhakra in the previous months, the sudden rise and fall in water levels during August, all these strongly point to the failure of a dam on the river. Since Sino-Indian relationship was at a low ebb during this period, field verification could not be done to confirm the findings.Flash floods in the Sutlej in 2005, reportedly due to landslips in Tibet necessitated evacuation of people and even shutting down of the NJP power generation activities resulting in heavy losses.The above instances highlight the need for India to be concerned about the Chinese activities in harnessing the rivers in the Tibetan region which influence the drought/flood conditions occurring in the border States. Interestingly, prior to 2000, floods of such intensity were not reported from the upper reaches of the Sutlej river whereas thereafter such floods have become frequent probably due to construction activities in this reach.In view of the increased interest China is showing to divert flows of some of the Himalayan rivers such as the Sutlej and the possible repercussions there of, India has to take steps to minimise the impacts such as reduction of flows caused by upstream diversions or flash floods resulting from breaches, sudden gate openings or even dam failures. Hence construction of a storage project near the border is a necessity to avoid pressing the panic button as and when China informs of the situation or even otherwise. (The writer is former Member-Secretary, Indian National Committee on Irrigation and Drainage)

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