BHUBANESWAR: Depleted water holding capacity of Hirakud Dam reservoir and extreme rainfall events induced by climate change can present an unprecedented challenge of flood management in Mahanadi river, if the medium level flood of August was any indication. Dam safety is a whole different issue in such a scenario.
That was the reason Central Water Commission (CWC) had recommended construction of additional spillways to protect world’s longest earthen dam. Yet, the first of the two proposed spillways is yet to get off ground; or rather far from it.
Construction work of the left spillway under the World Bank (WB)-funded Dam Rehabilitation and Improvement Project (DRIP) was left mid-way due to displacement issues. It was being carried out by a joint venture of Tata Projects Limited and Turkey-based AGE Group.
Sources said, after the Tata-AGE JV backed out of the `369 crore WB-funded project in 2020, the State government cancelled the work contract and decided to construct the additional spillway with its own funding through Odisha Construction Corporation (OCC). Subsequently, the project was also dropped from DRIP.
The estimated cost of the single spillway has now been revised to `786 crore. The project involves rehabilitation of 716 households and 1429 families which was the bone of contention behind the delay in carrying out the work.
While the JV has moved the tribunal against cancellation of work contract alleging delay in handing over of land for the project by the government, officials in Water Resources department said the firms withdrew after realising the bid amount was too less.
The spillway is critical to Hirakud’s health because it can decrease load of water on the dam in case the reservoir reaches a peak maximum flood (PMF) level caused by extreme precipitation events.As per available data, the CWC had reviewed the inflow design flood and pegged PMF at 69,632 cubic metre/sec (24.5 lakh cusec) in 1997. Against it, the existing total discharge capacity stands at 42,450 cubic metre/sec (15 lakh cusec) but effective discharge is about 36,806 cubic metre/sec (13 lakh cusec) due to operational constraint of few gates.This effectively means, in case of extreme rainfall events, the dam will have to grapple with management of about 12 lakh cusec flood water per second.
Hirakud dam safety spillway plan stutters
Additional Chief Secretary of Water Resources department Anu Garg said construction of additional spillways is priority of the government. “The work will start soon once the revised estimate gets Finance department’s nod,” she told The New Indian Express. Recently, the dam safety division had alerted Hirakud dam authorities about cracks in gate operation gallery and suggested drone based inspection for frequent monitoring of seepage quantity and further study of foundation gallery, gate shaft and sluice barrels.
Though survey was to be taken up at least once in every five years, it pointed out, no fresh survey for mapping of new cracks and checking status of old cracks has been undertaken since 1999. Chief Engineer of Mahanadi basin Anand Chandra Sahu said, revised estimate for the first additional spillway is in the final stage of approval. “Since the revised estimate is more than 15 per cent of the primary estimate, the Finance department sought some clarifications, which we submitted recently. Hopefully, the OCC will soon get the administrative and financial approvals soon,” he said.
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