Explainer: Desilting Bhakra’s Gobind Sagar

The Bhakra Beas Management Board (BBMB) has initiated the process to desilt the Gobind Sagar reservoir of Bhakra Dam for the first time since the dam became operational in 1959. The proposal marks a significant intervention in the management of one of North India’s most important multipurpose river valley projects.What’s being plannedThe BBMB has floated an Expression of Interest (EoI) to begin large-scale desilting of the Gobind Sagar reservoir. The work is proposed at two locations in Himachal Pradesh: Lunu in Bilaspur district and Seer Khad in Una district.According to estimates, around 150 million cubic metres (MCM) of silt is available for excavation at each of these sites. However, officials acknowledge that it will not be feasible to remove the entire quantity. At best, if everything works according to plan, a contractor may be able to excavate only 4 to 5 MCM per year.Desilting operations can be carried out only for about five months annually, when the reservoir’s water level recedes sufficiently to permit mechanical excavation.The BBMB has placed the responsibility of obtaining the necessary No Objection Certificates (NOCs) and environmental clearances on the contractor executing the project.The Himachal Pradesh government has given its consent and will receive a royalty of approximately Rs 150 per tonne of silt extracted. If higher commercial value is realised, revenues may be shared among the BBMB partner states of Punjab, Haryana and Rajasthan.Why it is necessaryThe primary reason for desilting is the loss of storage capacity. Since its commissioning decades back, the reservoir has lost nearly 25 per cent of its storage capacity due to silt deposition.As per the original design, the dam was expected to receive about 33.61 MCM of silt annually. However, actual inflow has averaged around 39.01 MCM per year, roughly 6 MCM higher than anticipated.Over the decades, this excess sediment load has accumulated significantly. Several factors are believed to have contributed, including rapid construction activity and road building in Himachal’s mountainous terrain, increased soil erosion due to deforestation and slope destabilisation.The construction of the Kol Dam upstream between 2003 and 2015 also led to a sharp rise in silt inflows. Although inflows got reduced briefly after the completion of Kol Dam, they began rising again after 2018, apparently because of intense construction activity in the region.Reduced storage capacity affects hydropower generation efficiency, flood moderation capability, irrigation supply reliability and long-term structural safety planning. Given the strategic importance of Bhakra Dam for northern India’s water and power security, restoring part of the lost capacity has become a priority.What the process entailsThe plan involves mechanical excavation of exposed silt deposits when water levels are low. The extracted material may be used for highway construction, infrastructure embankments, land filling and other civil engineering purposes.The BBMB has written to the Union Ministry of Road Transport and Highways seeking to make the use of dam silt mandatory in national highway construction. If approved, this could create a stable demand for the excavated material and potentially reduce pressure from illegal sand and gravel mining in Punjab and Himachal.The key challengesWith hundreds of MCM already deposited, the proposed annual removal of 4-5 MCM is relatively modest. Restoring significant capacity will take years, if not decades.Desilting is possible only when reservoir levels are low, restricting operations to roughly five months annually.Multiple NOCs and compliance with environmental regulations could delay execution.Moving millions of tonnes of silt from the hilly terrain to end-use sites will require substantial infrastructure planning.Model to followSome smaller reservoirs and barrages across states like Maharashtra and Telangana have experimented with commercial desilting linked to construction use, but Bhakra would be among the largest such attempts in the country.Globally, countries like Japan and Switzerland use sediment flushing and sediment bypass tunnels in mountainous river systems. However, those techniques are typically integrated into dam design unlike Bhakra, which was not originally built with large-scale sediment evacuation systems.The desilting project’s success will depend on environmental clearances, market viability of extracted silt, and sustained inter-state cooperation. If managed effectively, it could set a template for sediment management in other ageing reservoirs across India.

Explainer: Desilting Bhakra’s Gobind Sagar

If managed effectively, it could set a template for sediment management in other ageing reservoirs across India

Lalit Mohan

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