The Central Water Commission (CWC) has suggested review of the rule curves of major reservoirs to ensure effective flood risk management.
“Rule curves (specifying levels to be maintained in the reservoir at different times in a year) of major reservoirs where flood cushion is not in-built need to be reviewed to have some dynamic flood cushion for major part of the flood season. This holds true for Kerala too,” Sharad Chandra, CWC Director, Flood Forecast Monitoring, told The Hindu in an email interview.
“The rule curves for three major reservoirs in Kerala that include Idduki, Idamalayar and Kakki have been reviewed and reformulated with consideration of flood moderation in consultation with the CWC,” he said.
Stating that faulty reservoir operation remains a challenge in minimising the flood risk, Mr. Chandra said dams by design did not cause flooding if the reservoirs were operated as per some standard operating procedure/operation manual/rule curves, which provide different levels to be maintained at different times in a year.
“If the reservoir levels are quite high during the initial and middle months of a flood period, then it is tantamount to inviting trouble. Filling of reservoir should generally be slow during the initial period of the flood season and aggressive filling should be done during the end of the flood season. Inflow forecast should be utilised for real-time operation of reservoirs. It helps in pre-emptying the reservoir to avoid flooding-like situation downstream,” he said.
An Emergency Action Plan for dam break/extreme flood situations should be ready. “It will include flood inundation maps, flood waves and time analysis. The channel encroachment in downstream stretches of a dam should be removed,” he said. On whether Kerala would face another flood in the upcoming monsoon season, Mr. Chandra said there were evidences of increasing number of high intensity rainfall event varying spatially as well as temporally all over the country. “Such events lead to flash floods. Urban flooding due to storm water drainage congestion (pluvial in nature) has also become common in towns/cities due to such extreme meteorological events. Prediction (forecast with sufficient response/ lead time) of such floods is not possible,” he said.