During the 2018 August floods, the Idukki reservoir received a heavy inflow, with 33 feet of water within a period of four days.

An aerial view of Idukki reservoirPic credit: Biju Kalayathina
news Kerala Rains 2021 Sunday, October 17, 2021 - 16:04

The Idukki reservoir — the highest hydroelectric dam in Kerala — received over 4.25 feet of water within 24 hours between October 16 and October 17. According to officials, this is the first time after the Kerala 2018 flood that Idukki received such a high inflow of water in the dam. On Saturday morning, October 16, the water level was 2391.12 feet. It soon rose by nearly five feet, taking the water level to 2,395.56 feet, which is 91.38% of the storage level. The full reserve level is 2,403.50 feet.

On Friday, October 15, the water level had crossed the blue alert level (to keep watch). The dam safety wing issued a blue alert when the water level reached 2,390.86.feet. An orange alert is announced when the water level reaches 2,396.86 feet, followed by the red alert at 2,397.86 feet. At the time of publishing the article, the water level touched 2395.88 feet. On Saturday, the water level in the Mullaperiyar dam, upstream of the Idukki dam, was at 131.30 ft. The maximum permissible water level in the dam is 142 feet, as fixed by the Supreme Court in a 2014 judgment.

Peermade taluk in the Idukki district received the highest rainfall of 305.5mm in the past 24 hours. Climatologist Gopakumar Cholayil said that an automatic rain station at Peermade recorded 305.5mm rainfall in the past 24 hours. "This is the highest recorded rainfall in the state,” he said. “Usually, if an area records more than 100 mm of rainfall in one hour, it is referred to as cloud burst. In this case, it is a mini cloud burst, where there is more than 50 mm rainfall within two hours. The Kerala rains on Saturday in Kottayam and Idukki districts may be considered a mini cloud burst. The heavy downpour in a single period caused the flash floods and landslides," said Cholayil.

A dam safety official with the Kerala State Electricity Board (KSEB), which owns and manages the Idukki dam, said that the board and government are closely monitoring the water levels of the Idukki reservoir every hour. “The catchment area of the Idukki reservoir received extremely heavy rainfall and it resulted in the sudden rise of water level in Idukki reservoir within hours.  The central water commission allowed KSEB to follow the ‘dynamic flood cushion’ (to moderate floods) in Idukki. However, the unexpected rainfall resulted in an increase in the water level. The KSEB will also consider opening the Idukki reservoir at the red alert level if needed," the official explained, adding that the present water level is two feet below the red alert level of the dam.

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Earlier, the Central Water Commission had given KSEB permission to maintain the water level till the full reservoir level (FRL) in flood seasons. The FRL of the dam is 2403 feet. As per the dynamic flood cushion, the increasing water level should decrease within 10 days.

During the 2018 August floods, the Idukki reservoir received a heavy inflow, with 33 feet of water within a period of four days. The heavy inflow resulted in the opening of the dam. The 2018 dam safety wing data shows that a heavy inflow was recorded in the Idukki reservoir from August 15 to 18 in 2018. "Normally, 16 to 17 mm cube of water is needed for the water level to rise by one foot. But the inflow recorded on August 15 was 134 mm cube (7.8 feet), August 16 was 165 mm cube (10 feet), August 17 was 141 mm cube (8.29 feet) and August 18 was 111 mm cube (6.52 feet). It was then considered to be the first heavy inflow recorded in the Idukki reservoir. The normal inflow of the reservoir has 17 to 34 mm cube every rainy season, said the data.

Gopakumar Cholayil said that due to the climate crisis, Kerala will face extremely heavy rainfall, including landslides in the future. "The dam management should also account for climate-related issues. Earlier, we did not experience such extremely heavy rainfall in August and the following months. But since the 2018 August floods, climate change is clearly visible in Kerala. In future, we need to give more care to climate-related issues" said the climatologist.

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