GUWAHATI, Oct 5 - Blocking of the Brahmaputra river or its tributaries by the Chinese authorities in the Tibetan part of the Brahmaputra basin for consumptive use of their waters is sure to lead to the danger of significantly reducing the base flow or the lean period flow of the river during the non-monsoon season.
This is the observation made by internationally acclaimed river engineer Prof Nayan Sarma of IIT Roorkee. Prof Sarma studied the Brahmaputra from its source of origin in Tibet up to its extreme western point within the Indian territory in Dhubri district of Assam, under an European Commission-sponsored 18-partner international consortium named Brahmatwin, as the leader of the Indian scientists in the team. The study carried out in a five-year period between 2006 and 2010, covered various aspects like climate change, water availability and environmental disasters related with the Brahmaputra.
Talking to this correspondent, Prof Sarma said if the Brahmaputra is subjected to such an eventuality of reduced base flow, it will adversely impact the ecology of the entire river basin in India by affecting the aquatic habitats.
Besides, it will have a serious adverse impact on the river morphology of the Brahmaputra leading to heavy sedimentation and aggradation, and reduced water availability for numerous human activities, including navigation and drinking water supply during the non-monsoon period. And finally, this will have an adverse impact on the water quality and the river�s pollution abatement capacity, said Prof Sarma.
Elaborating the point of contribution of the Siang or the Dihang, known as the Yarlung Tsangpo in Tibet, which is a major stream of the three streams � Dihang, Dibang and Lohit � that have joined to form the Brahmaputra in Assam, Prof Sarma said about 30 per cent of the Brahmaputra�s flow, measured at Pandu in Guwahati, comes from Siang.
In the Tibet plateau, hardly about 400 mm of rainfall occurs annually. In contrast, in the Indian part of the Brahmaputra basin, annual rainfall ranges approximately between 1,500 mm and 2,500 mm. Thus, the monsoon flow of the Brahmaputra comes mainly from its about 33 tributaries in India.
Nevertheless, in the non-monsoon period, contribution of the tributaries is significantly reduced and this results in a base or low flow of 2,000 to 3,000 cubic metres per second (cumecs), compared to the overall flow of over 60,000 cumecs during the flood season as has been found at Pandu, said Prof Sarma.
It is very important to note that the base flow or the lean period flow of the Brahmaputra comes mainly from the glacier and snow melt run-off from Tibet and the groundwater from the Brahmaputra basin in India.
