CHANDIGARH: A high resolution study by the Indian Institute of Technology (IIT) Ropar has found that the overall storage loss due to silt accumulation in the Gobind Sagar reservoir of the Bhakra Dam is 19 per cent, significantly lower than the estimate made by the Bhakra Beas Management Board (BBMB).
The study, conducted at a 30 metre resolution for the first time in India and commissioned by the BBMB, found that the average rate of siltation in the reservoir is 30 million cubic metres (MCM) annually, which is lower than the reservoir’s original design estimate of 33.61 MCM per year.
The study further stated that the reservoir has retained significantly more storage capacity than what was claimed in the BBMB’s own assessment.
The study, conducted by a team of scientists led by Dr Reet Tiwari of IIT Ropar, found that the overall loss of storage capacity in the Bhakra reservoir was substantially lower than the estimates prepared by the BBMB’s Lake Survey department.
Speaking to this newspaper, Tiwari said, “As per our study, the overall storage loss is 19 per cent in the Gobind Sagar reservoir of the Bhakra Dam, while the live storage loss is only 12.9 per cent and the dead storage loss is about 38 per cent. The average rate of siltation is 30 million cubic metres (MCM) per year.”
Tiwari noted that the survey method used by the BBMB to calculate storage loss at the dam was an old one.
“Their survey method is old, which is a prevalent method followed by other organisations also. But the survey was done at a very high resolution, kind of the first time in India. We have surveyed at 30-metre resolution, enabling us to capture finer variations in the reservoir bed, whereas others use 610-metre resolution. Thus, all the undulations were captured accurately, providing a realistic siltation pattern. This type of survey can change actual water availability in India,” he said.
He added, “The use of advanced technology and higher resolution mapping has resulted in more precise estimates of sediment accumulation.”
Tiwari further said, “We have recommended to the BBMB to re-conduct this survey again after a three year interval to understand the siltation pattern more accurately. The de-siltation at the live storage at the dam can further improve water availability for Punjab, Haryana and Rajasthan.”
“The de-siltation survey of the dam is going on by our team and its report will be submitted after one month,” he said.
Sources said the BBMB, in its own survey, had estimated that the dead storage loss was 47 per cent, while live storage loss was assessed at 19 per cent and gross storage loss was pegged at 26 per cent. The board had estimated that the Bhakra reservoir receives around 39 million cubic metres (MCM) of silt annually.
The BBMB’s conventional surveys relied on cross sections spaced approximately 610 metres apart.
The contrasting findings have emerged at a time when the BBMB has already moved ahead with an ambitious plan to de-silt the Gobind Sagar reservoir, which has a total capacity of 6 billion cubic metres (BCM). The board has floated an Expression of Interest (EoI) for mechanical desilting at Lunu in Bilaspur district and Seer Khad in Una district of Himachal Pradesh.
It is estimated 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 has agreed to the proposal and will receive a royalty of around Rs 150 per tonne on the extracted material. If higher commercial value is realised from the excavated silt, the additional revenue may be shared among BBMB partner states Punjab, Haryana and Rajasthan.
A senior BBMB official, on condition of anonymity, said that there are mounds of silt up to 1,535 feet high within the reservoir and claimed that 40 BCM of silt is entering the dam annually against the initial estimate of 35 BCM.
