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Introduction
- The Chungthang dam in Sikkim recently collapsed due to heavy rains, causing major flash floods and loss of lives and property downstream.
- The incident highlights the importance of dam safety and proper environmental impact assessments for hydropower projects, especially in ecologically fragile areas like the Himalayas.
The recent collapse of the Chungthang dam in the Himalayan state of Sikkim has brought attention to the risks associated with building large dams in ecologically fragile areas. On October 4, 2023, heavy monsoon rains led to the catastrophic failure of the dam, resulting in massive flash floods downstream that claimed over 90 lives and caused widespread destruction. The incident highlights the need for stringent checks and balances when planning hydropower projects in seismically active and climate vulnerable regions like the Himalayas.
Chungthang Dam
| Sections | Details |
|---|---|
| Introduction |
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| Background |
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| Causes |
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| Effects |
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| Lessons Learned |
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| Conclusion | Chungthang incident: reevaluate Himalayan dam projects. Emphasize safety and sustainability from learned lessons. |
Background Information
Geography
- Location of Sikkim
- Teesta river and its tributaries
- South Lhonak lake glacier
Sikkim is a mountainous state in northeast India, nestled in the eastern Himalayas. The Teesta river, which originates from the South Lhonak lake glacier, is one of the major rivers flowing through the state. It cuts through rugged mountains and deep valleys, fed by numerous tributaries as it flows downstream into the Brahmaputra river. The Chungthang town, where the ill-fated dam stood, lies at the confluence of the Lachen and Lachung rivers, both glacial fed tributaries of the Teesta.
Chungthang Dam
- Part of Teesta III hydroelectric project
- Capacity and purpose
The Chungthang dam was an integral component of the 1200 MW Teesta Stage III hydroelectric project, commissioned in 2017. As a run-of-river project, the 817 m high dam was built to generate electricity by utilizing the gushing waters of the Teesta river. However, the massive artificial barrier across the river proved catastrophic once the swollen waters breached the dam due to heavy rainfall and other factors.
Chungthang Dam Overview
| Parameter | Details |
|---|---|
| Name | Chungthang Dam |
| Alternate Name | Chungthang Hydroelectric Project |
| Location | Chungthang, Sikkim |
| Part of | 1200 MW Teesta Stage III Hydro Electric Project |
| Commissioning Year | 2017 |
| Gross Height | 817 metres |
| Net Head | 778 metres |
| Type | Run-of-the-river hydroelectric project |
| Primary Electricity Consumers | Sikkim and West Bengal |
Chungthang Dam Location Map
Teesta River
- Origin, basin, tributaries
- Importance
The Teesta is the lifeline of Sikkim, cutting through the entire length of the state. It originates at an altitude of 7,000 m and flows for around 309 km before entering the Brahmaputra river in Bangladesh and joining the Bay of Bengal. With numerous tributaries draining the eastern Himalayas, the Teesta basin is prone to heavy precipitation, glacial melt and erosion leading to a high silt load. This makes the river geomorphologically unstable and unsuitable for mega dam projects.
Key Facts about Teesta River
| Parameter | Details |
|---|---|
| Type | Trans-Himalayan river |
| Flowing through | Indian states of Sikkim and West Bengal and Rangpur in Bangladesh |
| Relation to Brahmaputra | Tributary |
| Origin | Himalayas |
| Flow Path | Through Sikkim and West Bengal (India) and then enters Bangladesh |
| Merges into | Brahmaputra in Bangladesh |
| Total Length | About 309 kilometers |
| Main Tributary | Rangeet River |
Causes of Dam Collapse
Heavy Rains
- Unprecedented rainfall in region
- Breach of South Lhonak Lake banks
The primary trigger for the Chungthang dam failure was the unprecedented rainfall in the region preceding the disaster. In early October 2023, the South Lhonak lake area received over 500 mm of rainfall in just a few days – five times the usual precipitation. This led to the breaching of the moraine dam holding back the South Lhonak lake waters. The resultant outburst released a massive volume of water downstream, which proved to be the demise for the Chungthang dam.
Geological Factors
- Fragile Himalayan ecology
- Concerns over dam construction in area
The fragile geology and seismology of the Himalayas has long been a concern when planning major dams in the region. The Chungthang dam site lies in a highly unstable seismic zone. Experts have warned against blasting and tunneling activities associated with dam construction which can destabilize the already weak mountain slopes. The surrounding region is also prone to landslides and erosion which increase silting risks. Negligence of these geological factors may have compromised the integrity of the dam structure, making it susceptible to collapse.
Poor Impact Assessment
- Ignoring risks highlighted in previous studies
- Lack of disaster preparedness
Critics have alleged that the potential risks associated with the Chungthang dam were ignored during project planning. A 2021 report had clearly highlighted the expanding South Lhonak lake as a hazard for glacial lake outburst flooding which could compromise the downstream dam. Additionally, the tunneling and blasting activities may have exacerbated seismic instability in the region – a risk that does not appear to have been mitigated. Lack of a well-developed disaster preparedness plan for the dam further amplified the damage once disaster struck.
Effects of Dam Collapse
Loss of Lives and Property
- Flash floods downstream
- Damage to infrastructure
The flash floods resulting from the dam collapse caused immense loss of lives and property downstream. Over 90 people lost their lives while hundreds went missing as the 20-feet high surge of water hurtled through villages and towns in Sikkim and West Bengal. Vital infrastructure like 15 bridges, highways, transmission lines were destroyed cutting off the region. The Teesta Stage III hydropower station itself was severely damaged, resulting in power outages.
Impact Downstream
- West Bengal, Bangladesh affected
Apart from Sikkim, the deluge caused by the dam failure created havoc in downstream districts of West Bengal as well as parts of Bangladesh along the Teesta river basin. Thousands were displaced from their homes as the raging waters flooded habitations in the Siliguri region of West Bengal. There was also loss of agricultural land and cattle in both states.
Relief Operations
- Evacuations, compensation by govt
In the aftermath, rescue and relief operations were launched by the national disaster response agencies and the army. Relief camps were set up for displaced people and urgent funds were allocated by the Centre for rehabilitation. However, the scale of devastation made relief efforts very challenging.
Lessons and Way Forward
- Need for detailed geological surveys before dam construction
- Accounting for climate change factors
- Improving disaster preparedness
- Developing climate resilient infrastructure
- Ensuring proper rehabilitation before large projects
- Promoting renewable energy alternatives
Detailed Geological Surveys The incident highlighted the need for extensive geological studies before building dams in seismically sensitive areas. Proper impact assessment studies should account for climate change factors like extreme weather events.
Improving Disaster Preparedness A disaster management plan for dam breaches must be put in place, coupled with early warning systems and evacuation protocols for high risk zones.
Climate Resilient Infrastructure Dams and other infrastructure should factor in climate change projections on precipitation, landslides etc. to reduce vulnerability. Dam designs may need modification to handle increased water volumes.
Renewable Energy Alternatives Over-dependence on large hydroelectric projects can be risky. Promoting decentralized renewable sources like solar and wind energy must be encouraged to meet sustainable development goals.
Final Thoughts
- The Sikkim dam collapse is a wake up call for improving safety standards and learning from such incidents to build climate resilient infrastructure.
The Chungthang tragedy is a wakeup call to re-examine dam building activities in the Himalayas, and develop climate resilient infrastructure and energy solutions for the future. We must learn from such disasters to ensure proper planning, regulation and safety protocols.
