Hirakud reservoir has lost 24 per cent water holding capacity, says latest hydrology survey

The rising rate of sediment deposit is attributed to rapid soil erosion in the upper catchment of Mahanadi river.
Hirakud reservoir
Hirakud reservoir

BHUBANESWAR: Hirakud reservoir has lost 24 per cent of its water holding capacity, a latest hydrology survey says. If sedimentation study using optic and microwave remote sensing technology is any indication, live capacity of the reservoir has come down by 1,442.88 million cubic metre (m cum) during the last over six decades. The reservoir’s capacity loss is estimated at around 24.7 per cent in last 64 years due to continuous sedimentation and absence of corrective measures to clear deposits.

The study conducted by National Institute of Hydrology (NIH), Roorkee’s regional centre at Kakinada during 2018-2020 under the National Hydrology Project indicates that live capacity went down from 5,842.88 m cum in 1956 to around 4,400 m cum in 2020. The longest earthen dam in the world, Hirakud has been at the centre of intense flood management debate after the August deluge in Mahanadi river hit the State. It also happens to be the only flood controlling structure on Mahandi, the State’s lifeline.

At the core of the concern are extreme rainfall events - now occurring with alarming frequency due to climate change - that could trigger exceptional challenges of flood.The rising rate of sediment deposit is attributed to rapid soil erosion in the upper catchment of Mahanadi river. The sedimentation rate was around 22 m cum per year during the study period. The 1,442 m cum can also be read as the total silt load in the reservoir.

Principal investigator of the study Dr VS Jayakanthan said the study was conducted using the remote sensing technology that provides timely information regarding the estimated water spread area after the occurrence of sedimentation and sediment distribution pattern in the reservoir. “The study report was submitted to the Government of India last year. Once it is released after thorough verification by a team of experts, it will be shared with Odisha government,” he told The New Indian Express.

Another study carried out using area-reduction method in 2016 had predicted that the loss in live, gross and dead storage of the reservoir will be 58 per cent, 63 per cent and 100 per cent, respectively, of their original capacities by 2057, which represents 100 years of impounding of water in the reservoir.

The researchers’ team of IIT Kharagpur led by Prof Dhrubajyoti Sen analysed reduced trap efficiency, observed and projected capacity curves, rising reservoir bed level and capacities of different storage zones for various projected years.

“As per Brune’s trap efficiency and step method, the gross storage zone of Hirakud reservoir will be completely depleted and the reservoir bed level will rise to the full reservoir level of 192.02 metre by 2110 if the present sediment inflow rate continues without regular flushing of the deposited sediment,” the study revealed. Projection of numerical results indicates a complete loss of reservoir operational life due to sedimentation by around 2150.

However, the dam authorities refused to buy the claims. Chief Engineer of Mahanadi basin Anand Chandra Sahu said sedimentation is a natural process and de-siltation of a reservoir like Hirakud is unlikely to be cost effective.

“The rate of sedimentation has come down in the last few years after a number of structures were constructed in the upper catchment areas. The storage capacity will never deplete completely due to the under sluice system through which flood water is released every year as it cleans sediments in the lower 40 km part of the 83 km long reservoir,” Sahu reasoned.

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