Reservoir capacity loss 38%, not 47%: IIT-Ropar defies BBMB silt claims
Board set for 1st major desilting of Gobind Sagar Lake since 1959
A study by the Indian Institute of Technology (IIT), Ropar, has countered the Bhakra Beas Management Board’s (BBMB) estimates on the extent of silt accumulation and storage loss in the Gobind Sagar reservoir of Bhakra Dam. The study says the reservoir has retained significantly more of its storage capacity than claimed in BBMB studies.
The study, conducted by a team of scientists led by Dr Reet Tiwari of the IIT, has found that the overall loss of storage capacity in the Bhakra reservoir is substantially lower than the estimates prepared by the BBMB’s Lake Survey Department. The findings assume significance as the BBMB has initiated the process for the first-ever large-scale desilting of the Gobind Sagar reservoir since the dam became operational in 1959.
According to the report accessed by The Tribune, the IIT team has estimated the overall capacity loss of the reservoir at 38 per cent, compared to 47 per cent estimated by the BBMB. The study has also reported that the loss of live storage stands at 13 per cent, considerably lower than the 19 per cent assessed by the BBMB.
Similarly, the IIT study has pegged the loss of gross storage at 19 per cent, against the 26 per cent estimated by the BBMB.
The research has also contradicted the BBMB’s assessment of annual silt inflows into the reservoir. While the board has estimated that the Bhakra reservoir receives around 39 million cubic metres (MCM) of silt annually, the IIT-Ropar scientists have assessed the inflow at 31 MCM, which is even lower than the reservoir’s original design estimate of 33.61 MCM per year.
Senior BBMB officials attributed the variation in findings to the advanced survey techniques adopted by the IIT team. Speaking on the condition of anonymity, they said the institute had used modern bathymetric surveys, drone-based mapping and much denser cross-sectional measurements to assess sediment deposits.
According to the officials, the IIT scientists conducted surveys at intervals of about 30 metres, enabling them to capture finer variations in the reservoir bed, whereas the BBMB’s conventional surveys relied on cross-sections spaced about 610 metres apart. The use of advanced technology and higher-resolution mapping, they said, had resulted in more precise estimates of sediment accumulation.
The contrasting findings have emerged at a crucial stage, with the BBMB moving ahead with an ambitious plan to desilt the Gobind Sagar reservoir. The board has already floated an expression of interest for mechanical desilting at Lunu in Bilaspur district and Seer Khad in Una district of Himachal Pradesh.
Officials estimate that nearly 150 MCM of silt is available for excavation at each site. The contractor executing the work will be responsible for obtaining environmental clearances and other statutory approvals. It was decided that Himachal Pradesh would receive a royalty of around Rs 150 per tonne on the extracted material. If a higher commercial value is realised from the excavated silt, the additional revenue may be shared among the BBMB partner states of Punjab, Haryana and Rajasthan.
Despite the differing estimates of storage loss, experts agree that sediment management has become increasingly important for maintaining the long-term efficiency of the Bhakra project, which remains one of northern India’s most critical sources of irrigation water, hydropower generation and flood moderation.
