A major landslide hit an under-construction dam in Arunachal Pradesh on Friday, causing significant disruption to a 2,000 megawatt (MW) hydroelectric project and diminishing water flow in the Subansiri river in Assam. The landslide occurred about 300 meters from the dam and blocked a diversion tunnel in the Subansiri river, resulting in a sharp reduction in downstream water flow.
This particular diversion tunnel was the only one in use at the Subansiri Lower Hydroelectric Project, as the other four diversion tunnels had already been blocked earlier, according to the National Hydroelectric Power Corporation (NHPC).
The incident has raised concerns in Assam’s Lakhimpur district, which is situated downstream of the dam in Arunachal Pradesh. The government has issued an advisory, urging people to refrain from activities like fishing, swimming, bathing, and boating. Additionally, people have been asked to keep their cattle away from the river.
NHPC officials have stated that the river is expected to return to its normal flow by the evening. “The current river flow of 997 cubic meters per second is being stored in the reservoir, and the water level reached 139 meters by 1 pm. It is expected that the water level will reach 145 meters by the evening, and the river will return to flowing through the spillway normally,” the statement read.
The blockage of the diversion tunnels, used for redirecting river water during construction, had been a concern for the project over the past decade. Local activists and residents had expressed worries about potential downstream impacts of the dam, leading to protests.
In April last year, the powerhouse protection wall of the dam had collapsed due to tail race channel construction activities. The tail race channels, responsible for releasing water back into the river after passing through turbines, are located on the right bank of the river in Arunachal Pradesh.
Over the last three years, the project site has experienced four significant landslides. The NHPC commenced construction of the project in January 2005 but faced a lengthy halt from 2011 to 2019 due to ongoing protests.
According to company estimates in 2020, the project’s cost, originally scheduled to be commissioned in 2012, had surged to approximately ₹20,000 crore from the initial ₹6,285 crore. This incident also follows a recent dam breach in Sikkim, which resulted from a glacial lake outburst and led to flash floods and casualties, raising concerns about the safety of such projects in the region.
