Following a review by the Central Water Commission (CWC) over the design of the flood gates of Pandoh Dam in Mandi district of Himachal Pradesh, the Bhakra Beas Management Board (BBMB) has proposed construction of twin tunnels at the dam to provide an additional route for safe discharge of floodwater.
Meanwhile, the Himachal Government has started mapping potential downstream flood-affected areas through satellite and remote sensing to assess risk factors and alert the public in advance.
Sources pointed out that the present existing spillway arrangement at the dam does not have adequate capacity to safely discharge the revised flood volume, prompting the Bhakra Beas Management Board to explore an additional discharge mechanism.
The review by the Central Water Commission pointed out that the volume of Probable Maximum Flood (PMF), the maximum flood considered possible at the site, had increased due to the changing monsoon patterns and increased incidence of cloudbursts and flash floods.
Sources further added that as per the preliminary proposal, the proposed tunnel system plans to discharge approximately 2,000 cumecs (cubic metres per second) of water and could be approximately 1,200 meters long, providing a bypass route from upstream of Pandoh Dam to downstream, avoiding Pandoh town and exiting beyond the market area.
An official said there is a need to ensure safe discharge of additional floodwater and the need to create an alternative flood-discharge route without altering the old dam structure.
"Modifications to the dam cannot be made directly. Instead, an alternative route is being considered to flush out excess water safely through another route in case a flood situation arises."
It is learnt that a proposal seeking administrative approval for preparing a detailed project report (DPR) has been submitted to the senior officials of the BBMB.
The proposed project is presently at an initial stage, with detailed investigations yet to begin.
In June this year, the BBMB issued an alert that water is being released from the dam after a rise in water inflow into the reservoir and a safety advisory was also issued to the people to stay away from the Beas River.
The excess water has been released from the dam on several occasions, which affected low-lying areas in Mandi, Hamirpur and Kangra districts.
Many previous incidents had resulted in flooding, damage to property and loss of life. Environmentalist and Himalaya Niti Abhiyan coordinator Guman Singh said that the increasingly unpredictable weather patterns have heightened risks to the safety of dams.
"The glacier collapses can trigger massive floods due to global warming, and it cannot be claimed that the dams are safe, particularly when they are located in a highly seismic zone,’’ he said.
Also, the Himachal government will strengthen early-warning systems with the aim of translating monitoring and hazard information into actionable warnings for people living downstream.
As per a risk assessment by the National Remote Sensing Centre (NRSC), Hyderabad, Sissu village falls in the red zone, and the steep slope between the Geepang Gath lake in Lahaul-Spiti and the village could result in accelerated flow of water and debris in case of a lake burst.
The lake has been declared highly vulnerable by the National Disaster Management Authority (NDMA).
The detailed downstream flood zonation of this glacial lake has been initiated to identify the red, yellow and green zones in proximity to the river. It is learnt that a few of the villages which could face threat from a likely lake burst include Sissu, Goshal and Tandi.
