Overview:
On 27 October 2023 a landslide blocked the diversion tunnel at the site of the under construction Subansiri Lower Hydroelectric Power Dam
The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
On Friday 27 October 2023 a major landslide occurred at the site of the Subansiri Lower Hydroelectric Power facility in Assam, northern India. The landslide is significant because it has blocked the last remaining diversion tunnel that has been used to transport the flow of the river around the site of the dam during construction.
The landslide was captured on at least two videos that have been uploaded to Youtube:-
The blockage of the diversion tunnel meant that water was unable to flow through the site. The Indian news site Northeast Now has a good account of the events, including detail about the blockage of the Subansiri River.
The location of the site is [27.55482, 94.26049]. This is a Planet Labs image of the dam, collected on 26 October 2023:-
Note the landslide scar to the northeast of the dam – this is the site of the most recent failure – and the water emerging from the tunnels below the dam on the eastern side of the channel.
By contrast, this is an image from 29 October 2023, after the landslide:-
The water level behind the dam was notably higher on 28 October 2023, and was was now flowing over the spillway of the dam. There is no immediate crisis, although the period of zero flow might have caused ecological damage.
The troubling aspect of this event though is the failure to manage the slopes. There are reports that eight diversion tunnels have been blocked by slope failures, and there are videos of other landslides at the site:-
Reference
Planet Team (2023). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/