Idukki: A view of the Idukki Dam as water level continued to rise in the reservoir in Iduki dam area of Kerala on Friday, August 10, 2018. (PTI Photo) Idukki: A view of the Idukki Dam as water level continued to rise in the reservoir in Iduki dam area of Kerala on Friday, August 10, 2018. (PTI Photo)

If the intense spell of rainfall witnessed last month in Kerala was to recur, “dams cannot provide any relief,” the Central Water Commission said on Saturday. The CWC’s report on the floods will be released on Monday.

CWC’s director hydrology (south) NN Rai, who conducted the analysis for the Kerala floods, said: “If again such type of rainfall comes, then dams cannot provide any relief.”

Rai said that CWC had investigated the role of all reservoirs and concluded that dams had not aggravated or abated the situation. Speaking at an event organised by the National Institute of Disaster Management, Rai said: “Rule curves are essentially required for all the dams, that is what we are recommending in our report also. For flood moderation, we should not count all 57 dams, but those with storage greater than 200 million cubic metres.” He listed seven reservoirs — Idukki, Idamalayar, Kakki, Mullaperiyar, Chaliyar, Bharathappuzzha and Valapuram — that fall under this category.

The Indian Express had reported that the CWC had given a clean chit to dam management in the state, and pegged congestion in the Vembanad Lake as one of the main reasons for worsening the flood situation.

Rai said that the lake had a capacity to store 2 billion cubic metres. “But because of encroachment in the area and rice cultivation around it, this has shrunk to 0.6 BCM,” he said. “The rising water levels in the lake impacted the entire hydro-dynamics of the rivers that drain into it,” he added.

“When such types of floods occur, one should try to analyse and prepare a rationale of rainfall scenario which will give you a true picture,” Rai said, adding the last time Kerala witnessed such rainfall was in 1924.

Between August 15 and August 17, which CWC identified as one of the worst rainfall spells, Rai said that river basins such as Periyar received a cumulative rainfall over three days of 588 mm (compared to 604mm in 1924), Pamba 538 mm (551 mm in 1924) and Bharatppuzha received 373 mm (378 mm in 1924). “These are the storms which we call standard project storm,” he said.

An SPS is the heaviest rain storm which has occurred in that region as per rainfall records. “Dams are designed for flood moderation of 25 to 100 year period only,” he said.

Rai disagreed with the main speaker of the event, Himanshu Thakkar from the South Asia Network on Dams, Rivers and People, who said that Idukki reservoir could have been managed better to moderate the floods. “I disagree with this argument. 2,563 cumec was the peak recorded at Idukki, they had released 1,500 cumec, in that way they had curtailed peak of 1,000 cumec. In three days, 435 million cubic metres was the run-off that came into the dam, and out of that, 375 MCM was released, so 60 MCM was restored,” Rai said.

Speaking on ‘Reservoir Operation and Flood Risk Management’ in the context of Kerala, Thakkar said that it was “not good enough” if authorities made the argument that outflows from dams equalled the inflow during floods. He put forth a strong case for how dams can be managed to moderate floods. He had said that rule curves, which determine how the dams are filled up during the monsoon period, should be put in place or updated.

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