Silt threatens Bhakra Dam, holding capacity dips 25%

With the storage capacity at the Bhakra Dam down by about 25 per cent over the years due to inflow of silt and debris, the Bhakra Beas Management Board (BBMB) has initiated a massive project to get portions of the reservoir desilted.

“The proposal to desilt the reservoir has been approved by the board. We will be issuing a tender shortly to invite bids for the purpose,” a senior BBMB official said. He added that as the area fell in Himachal Pradesh, discussions were also being held with the state government on royalty, availability of land for infrastructure, transportation of silt, and its possible use for landfill or industrial purposes.

Given the mountainous terrain and irregular depth of the reservoir, it would be a long-drawn and highly technical project. The BBMB official said the dry or shallow areas around the perimeter could be excavated when the water level was low during the depletion period.

The designed gross storage capacity of the Bhakra reservoir, including the dead storage capacity, that is the level below which water cannot be released for power generation, is 9.8 billion cubic meters (BCM). The present live storage capacity at full level, according to the Central Water Commission, is 6.2 BCM.

The construction of the dam, which lies on the Sutlej in Himachal Pradesh, began in 1948. It became operational in 1963. With an installed capacity of 1,379 MW and an irrigation potential of 6,76,000 hectares, it is a vital establishment for this region.

Bhakra’s reservoir, christened Gobind Sagar, is over 90 km in length, with a maximum depth of 534 ft. A large part of the dam’s catchment area, spread over 57,000 sq km, lies in the barren, partially sandy areas of Lahaul and Spiti, upper Kinaur and adjoining Tibet. As a result, a lot of silt and loose debris get swept into its flow. Massive deforestation, cultivation and construction along the Sutlej’s course as well as its tributaries and rivulets that feed the main river have added to the problem, especially during rains.

According to BBMB officials, 38-39 million cubic meters (MCM) of silt flows into the reservoir annually, which is higher than the rate of 33-34 MCM envisioned at the time of the dam’s impoundment in 1958.

Experts say if silt inflow continues and no remedial measures are undertaken, the capacity of the reservoir could be further reduced by 35-40 per cent by 2050.