Recent flash floods originating from Lhonak Lake in North Sikkim, India, have caused significant destruction downstream, including the destruction of the 1,200 MW Teesta Urja dam, 11 reported fatalities, and over 120 people missing.
In 2013, scientists from the National Remote Sensing Centre in Hyderabad reported that Lhonak Lake, located at an elevation of 5,245 meters above sea level, was “highly vulnerable” to a GLOF event with the potential for extensive damage to life and property downstream. The report warned of the possibility of “flash floods” with critical infrastructure like dams and powerhouses susceptible to damage.
The vulnerability assessment also highlighted the risk to townships such as Chungthang, Dikchu, Singtam, and Rangpo, with potential loss of life and property.
Several field expeditions over the years had studied the problem, with the first in August 2014 by a team from the Snow and Avalanche Study Establishment (SASE), Sikkim Department of Science and Technology and Climate Change, and other stakeholders. This team reiterated the threat of “devastation” and recommended a mitigation management plan, including “siphoning” as a short-term measure.
Siphoning involves the use of inverted pipes to allow atmospheric pressure to force water from a reservoir over an embankment dam and release it from the other end of the pipe.
A second expedition in September 2016, led by the Sikkim State Disaster Management Authority (SSDMA), the Indo-Tibetan Police Force, and the Students Education and Cultural Movement of Ladakh, concluded that “engineering intervention was not feasible” due to the risk of melting dead ice.
To address the situation, Sonam Wangchuk was appointed as a consultant to implement the siphoning process, which included installing high-density polyethylene (HDPE) pipes in three pipelines, each between 130 to 140 meters long, to pump out water at a rate of 150 liters per second. A water level monitoring system was also installed.
Flash Floods in Sikkim Result in Casualties, Missing Persons, and Infrastructure Damage
Flash floods triggered by a cloudburst over Lhonak Lake in north Sikkim, India, have caused significant casualties, missing persons, and infrastructure damage, according to officials. The flash floods occurred around 1:30 am local time and were exacerbated by the release of water from the Chungthang dam. As of the latest reports:
•At least ten people have died, all of whom were civilians, with three of the deceased washed up in North Bengal.
•80 people are missing, including 22 army personnel.
•Over 3,000 tourists from different parts of India are reported to be stranded in various parts of Sikkim.
•Workers employed with Teesta Stage III dam in Chungthang were stranded in tunnels of the dam.
•The road infrastructure has suffered extensive damage, with 14 bridges collapsed, nine under Border Roads Organization (BRO), and five belonging to the state government.
•Scores of people missing and injured have been reported from various areas in Sikkim.
•A child’s body was among those found in the floodplains of the Teesta River.
•Prime Minister Narendra Modi spoke to Chief Minister Prem Singh Tamang and assured all possible support.
•Defence Minister Rajnath Singh also expressed concerns for the missing army personnel.
•The Sikkim government has declared the natural calamity as a disaster.
•The release of water from the Chungthang dam led to a sudden increase in water levels downstream, damaging infrastructure and submerging vehicles.
•Parts of National Highway-10, the main link between Sikkim and the rest of the country, were washed away.
•A flood alert has been issued for North Bengal and Bangladesh, through which the Teesta River flows.
Efforts are underway to rescue those stranded, locate the missing army personnel, and provide relief to affected areas. The flash floods have caused widespread devastation, and authorities are mobilizing resources to address the immediate concerns and challenges posed by the calamity.