As the northeast monsoon is slowly withdrawing from Kerala, the Idukki reservoir, one of the largest in Asia, has record storage for the month of December. The water level reached 2,401.58 ft on Tuesday.
As per official data, the highest water level in December earlier was in 1981 and 1992. On December 1, 1981 the water level was 2,401.37 ft and in 1992, 2,401.23 ft. However, during these two years, the water level was receding after reaching the highest level in November.
The Idukki reservoir recorded the highest water level on November 13, 1981 at 2,403.12 ft and on November 17, 1992 at 2,402.88 ft. (The full reserve level is 2,403 ft). The storage was 98.29% in the reservoir on Tuesday.
“If the heavy rain spell was continuous, the water level might have increased suddenly and water would have been released to keep the upper rule level set by the Central Water Commission (CWC) in accordance with the progress of the monsoon. Had there been heavy rainfall for a short period as happened in August 2018, water would have been drained out as the upper rule curve was below the present level of the FRL,” says M.P. Saju, Assistant Engineer, Dam Safety, Kerala State Electricity Board (KSEB).
This year, the rainfall was in a phased manner and the rise in water level in Idukki occurred over an extended period.
The CWC has fixed the rule curve to avoid chances of sudden opening of the dam resulting in a flood situation. The power generation at Moolamattom was also at the maximum during a monsoon season.
The long spell of both southwest and northeast monsoons also helped in keeping the storage level high during the end of the monsoon period.
The water year starts on June 1 as per the KSEB calendar and the water level usually peaks in October or early November and will start to decline by December. The intermittent water release from the Mullaperiyar dam also contributed to the high storage level as it was not a discharge of water at once.
Mr. Saju says high rainfall during the withdrawal period of the northeast monsoon has also resulted in the high storage level in December.