GUWAHATI, Jan 1 - Prof Nayan Sarma of the IIT Roorkee has warned that melting of the numerous upstream glaciers, accompanied by growth of unconsolidated landslide-induced dams on the Yarlung Tsangpo over time, with possible catalyst of an earthquake, can spell severe disaster in Arunachal Pradesh and Assam. Prof Sarma of the Water Resources Development and Management Department of the IIT Roorkee, has been studying the Himalayan rivers, particularly the Brahmaputra, for the past about three decades. Prof Sarma, who was talking to this correspondent, maintained that to avoid such a catastrophic disaster, the Indian Government, in close cooperation with Chinese authorities, should immediately start round-the-clock monitoring of the affected zone with regard to landslide activities, glacial dynamics etc.
Holistic scientific assessment of the problem at hand is also required, along with vulnerability analysis. Besides, multidisciplinary technical feasibility of the pre-emptive, controlled blasting of the temporary dams, in safe predetermined measured steps, may be explored by carefully working out the flood wave speed, using standard dam break analysis, applying high resolution Digital Elevation Model (DEM), along with satellite-borne LiDAR data for accurate lake volume assessment.
Urgent relief and evacuation measures for disaster management may be planned in vulnerable areas, on the basis of findings from the above studies.
With joint Indo-China cooperation, a modern early warning system should be set up permanently to cover Eastern Tibet region as well as the downstream riparian Indian states, said Prof Sarma.
Knowledge of lake water volume is prerequisite, along with river hydrographic data, to conduct dam break analysis for assessment of flood devastation in downstream areas.
To assess the volume of stream flow impounded in the above dams, it is essential to make measurements not only of length and width of the dam surface, but also on the lake bathymetry profiles involving water depth variations.
Elaborating upon the threat, Prof Sarma said, “Worst possible scenario that can happen would be if the above unconsolidated dams collapse when the Siang River carries its maximum flow of 30,000 cubic metres of water per second (cumec) in the rainy season and the dam-breached additional flood gets superimposed on it.”
An initial perusal of the LANDSAT-8 Satellite Imagery of December 21, 2017 of the Gyala Peri – Namcha Barwa Gorge part of the Yarlung Tsangpo revealed the occurrence of heavy landslides in the aftermath of the November 17, 2017 6.4 Richter scale earthquake and series of aftershocks.
The river length of the Yarlung Tsangpo between the affected landslide zone to Indian border at Tuting is hardly about 165 km and its elevation drop is about 1,300 metres, while the elevation drop up to Pasighat is of an overwhelming magnitude of 1,600 metres.