The Chungthang Hydropower Project usually refers to the Teesta Stage-III Hydroelectric Project, a major hydropower project located near Chungthang in North Sikkim.
It became widely discussed after the October 2023 South Lhonak Lake GLOF, which destroyed the project’s dam and triggered a larger downstream disaster in the Teesta basin.
Basic Profile
The project is built on the Teesta River, near the confluence of Lachen Chu and Lachung Chu close to Chungthang town.
Important facts include:
- Project name: Teesta Stage-III Hydroelectric Project
- Common reference: Chungthang dam / Chungthang hydropower project
- Location: Chungthang, North Sikkim
- River: Teesta
- Capacity: 1,200 MW
- Type: high-head hydropower project
- Commissioned: 2017
- Installed units: 6 units of 200 MW each
- Reservoir capacity: about 5.08 million cubic metres
The project was one of Sikkim’s largest hydropower assets and an important part of the Teesta hydropower cascade.
Location in the Teesta Basin
Chungthang is located in the upper Teesta basin. The Teesta River system here is fed by Himalayan glaciers, snowmelt and high-altitude streams.
This geography gives the project high hydropower potential, but it also exposes it to Himalayan hazards such as:
- glacial lake outburst floods
- landslides
- flash floods
- high sediment load
- earthquakes
- extreme rainfall
- slope instability
The project’s location in the eastern Himalayan seismic and glacial environment makes disaster-risk assessment especially important.
Link with South Lhonak Lake GLOF
On 4 October 2023, a Glacial Lake Outburst Flood from South Lhonak Lake rushed down the Teesta basin.
The flood carried huge volumes of water, debris and sediment. When it reached Chungthang, it overwhelmed and destroyed the Teesta-III dam.
Scientific and institutional accounts identify the 2023 GLOF as the event that destroyed the 1,200 MW Teesta III hydropower dam at Chungthang.
The disaster was not limited to the dam. Once the dam failed, the reservoir water added to the flood surge and worsened downstream impacts.
Impact of the 2023 Disaster
The destruction of the Chungthang dam became one of the most serious examples of hydropower vulnerability in the Himalayas.
Major impacts included:
- destruction of the Teesta Stage-III dam
- damage to the underground powerhouse
- severe downstream flooding
- destruction of bridges and roads
- damage to NH-10 and other connectivity routes
- disruption of villages and settlements
- loss of lives and missing persons
- damage to downstream hydropower infrastructure
- heavy sediment deposition in the Teesta channel
A 2026 study described the project as a near-total asset loss after the 2023 GLOF, noting that the debris-laden surge overwhelmed the dam, breached its structure and inundated the underground powerhouse.
Why It Matters
The Chungthang case is important because it shows that Himalayan hydropower projects cannot be assessed only on electricity-generation potential.
They must also be assessed against changing climate and cryospheric risks.
The disaster exposed the risk of building large hydropower infrastructure downstream of expanding glacial lakes. As Himalayan glaciers retreat, glacial lakes can grow and become unstable. If such lakes burst, downstream dams, roads, bridges and settlements can face extreme flood surges.
The Chungthang dam failure therefore became a warning for hydropower planning across:
- Sikkim
- Arunachal Pradesh
- Uttarakhand
- Himachal Pradesh
- Ladakh
- other Himalayan river basins
Reconstruction and Current Status
After the 2023 destruction, reconstruction of the Teesta Stage-III dam has been taken up.
Reports from 2026 mention that reconstruction work is underway and that the new structure is being designed with a much higher flood-handling capacity. The earlier dam was reportedly designed for around 7,000 cubic metres per second of flood discharge, while the reconstructed dam is expected to withstand up to 20,000 cubic metres per second.
This redesign reflects the new reality that Himalayan infrastructure must account for extreme events, not just historical flow records.
Environmental and Social Concerns
The reconstruction has also raised concerns among local communities, environmental groups and researchers.
Key concerns include:
- whether GLOF risk has been fully reassessed
- whether dam safety standards are adequate for future extreme floods
- impact on downstream communities
- cumulative impact of multiple Teesta basin hydropower projects
- sediment and debris-flow risk
- seismic vulnerability
- rights and concerns of local communities, including Lepcha communities
- need for transparent environmental appraisal
The debate is not only about rebuilding one dam. It is about whether the Teesta basin can safely support large hydropower projects under changing Himalayan climate conditions.
Lessons from Chungthang
The Chungthang disaster underlines several lessons for Himalayan development.
Important lessons include:
- hydropower projects need basin-level risk assessment
- glacial lake monitoring must be linked with dam-safety planning
- early warning systems must be functional and last-mile connected
- dam design must account for extreme GLOF and debris-flow scenarios
- cumulative hydropower development needs stricter review
- downstream communities need evacuation plans
- climate change must be built into infrastructure design
- emergency reservoir operation protocols should be tested regularly
The project shows that “run-of-river” or high-head hydropower schemes are not automatically low-risk in glacial Himalayan basins.
Significance
The Chungthang hydropower project is significant because it sits at the intersection of energy security, climate risk and Himalayan ecology.
It was a major electricity-generation asset for Sikkim, but its destruction showed how vulnerable high-value infrastructure can be to extreme mountain hazards.
For India, the project has become a case study in why future Himalayan hydropower must integrate glacier science, GLOF modelling, seismic risk, sediment dynamics, community safety and climate-resilient engineering.
