Lhonak lake breaches banks after cloudburst, triggering massive outflow in Teesta basin
Ajay Banerjee
New Delhi, October 4
Ten persons have died while 82 others, including 22 Army personnel, are missing after a midnight cloudburst led to a breach in the Lhonak lake in north Sikkim, triggering flashfloods in the Teesta river basin. One of the jawans who was washed away was rescued 14 hours later in the evening. His condition is stated to be stable. The local administration has recovered 10 bodies and the number is expected to rise. Three of the dead were washed up in north Bengal.
- Several km of Siliguri-Gangtok highway totally destroyed
- Over half-dozen bridges, 40 Army vehicles swept away
- NDRF teams deployed, rain hampers evacuation
The floodwaters destroyed several kilometres of the vital Siliguri-Gangtok national highway (No. 10), while 40 Army vehicles were washed away. The road access to Nathu La, the pass on the India-China boundary located east of Gangtok, was snapped and more than six bridges on the highway were swept away. With hundreds of tourists stranded, IAF and Army helicopters were pressed into service to evacuate them but rain hampered the operations. A report of the state disaster management authority attributed the sudden flooding to the breaching of the Lhonak glacial lake in Mangan district of north Sikkim. This resulted in water levels rising with very high velocity downstream along the Teesta river basin in the early hours, reportedly causing heavy destruction in Mangan, Gangtok, Pakyong, and Namchi districts of the state.
Journal had Warned about threat in 2021
- Science Direct, a reputed journal, had warned that “Lhonak lake has been identified as potentially dangerous” in a paper published in May 2021
- Lhonak glacier is retreating and the lake formed from its waters is the largest and fastest-growing in the state, the study said
As the huge amount of water – from the cloudburst and the glacial lake — gushed down the Teetsa, a dam at Chungthang in Mangan district gave way, compounding the crisis. The downstream areas like Teesta bazaar were badly hit.
Dam gives way
- Cloudburst occurs around 1 am
- Glacial lake at Lhotak breaches its banks and half of its water drains out within minutes
- Water rushes down Teesta river
- Dam at Chungthang gives way, adding to the water flow
- BSF has evacuated people from low-lying areas in West Bengal
Around 1 am, major flooding of the Teesta river was reported from Chungthang. Within 90 minutes, the floodwaters had caused serious destruction to public properties, infrastructure and the communication network.
As the Lhonak lake at an altitude of 17,000 feet breached its banks, the water levels rose 15 metres per second. The central water commission measuring site at Malli in south Sikkim at 6 am recorded the water level at 227 metres, which was about 3 metres above the danger mark. Army jawans were probably caught unawares, either they did not get the time to escape or were swept away in their sleep.
The National Crisis Management Committee (NCMC) under the chairmanship of Cabinet Secretary Rajiv Gauba ordered the evacuation of tourists and people near the Chungthang dam on priority.
The National Disaster Response Force (NDRF) has already deployed three teams, while additional teams are on standby in Guwahati and Patna.