DIBRUGARH: There is a growing apprehension among the public and intellectuals regarding the safety of constructing mega dams in India, especially in Arunachal Pradesh, following the recent Glacial Lake Outburst Flood (GLOF) incident in the Teesta Valley in October 2023.
The technical aspects underlying the GLOF scenario in the Teesta Valley differ significantly from the existing glacial lakes and their potential impact on proposed dams in Arunachal Pradesh, particularly those constructed by NHPC.
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This concept can be comprehended further in the subsequent paragraphs.
The Teesta Basin harbours numerous glacial lakes upstream of the Teesta III dam (Chungtham Dam), which have been subject to periodic study due to their potential to impact dams through GLOFs.
In 2015, the Central Water Commission (CWC) conducted a study in collaboration with the National Remote Sensing Centre (NRSC), ISRO, titled “Status of Glacial Lakes & Water Bodies in the Himalayan Region of Indian River Basins”.
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A GLOF event originating from the South Lhonak lake in Sikkim, located approximately 70 km upstream of the Teesta III Dam, could have been triggered by various factors, including earthquakes, flash floods, glacier calving, or breaches due to the detachment of moraine sidewalls, or a combination of these events.
Most of the glacial lakes in the Subansiri, Siang, and Dibang river catchments are situated in the Chinese portion of these catchments, far from NHPC projects, thus posing an insignificant threat of GLOF-induced floods.
The topographic and catchment characteristics, as well as the locations of glacial lakes in river basins in Arunachal Pradesh, differ significantly from those in the Teesta Basin GLOF case.
Consequently, there is no likelihood of GLOF-induced flood disasters for projects in the Subansiri, Siang, and Dibang Basins in Arunachal Pradesh.
The distance of glacial lakes from NHPC dams results in the attenuation of GLOF floods to very low values.
Additionally, the mild slope of rivers leads to lower flow velocities of floodwater, allowing for higher travel time and more time to implement mitigation measures.
Moreover, the presence of substantial reservoir storage volume ensures that the GLOF volume is completely absorbed into reservoirs, posing no threat to dams or downstream populations.
Existing studies indicate that GLOF peaks at dam sites are even lower than average monsoon floods for NHPC projects in the Subansiri, Siang, and Dibang basins.