Kottayam: The water from the Idukki Dam constructed across the Periyar River was released on Tuesday, October 19, for the fifth time in history in view of the torrential rains and more rains predicted in its catchment areas.
The Cheruthoni Dam, which acts as its sole outlet, was first opened on October 29, 1981, then on October 12, 1992, August 9, 2018, and October 6, 2018.
So far the opening of the dam has always been in October.
In 1981, shutters were opened for 11 days. A total of 1221.222 Metric Tonnes (MT) of water was released to the Periyar river. In 1992, shutters were opened for 13 days and 2774.734 MT of water was released to the river. During the third time in 2018, shutters, which were opened on August 9, were closed on September 7. Dams were opened again on October 6, 2018, anticipating heavy rain. The dam was later closed once the weather forecast of heavy rain was withdrawn.
The Idukki reservoir is regulated by three dams — Idukki arch dam, Cheruthoni dam and Kulamavu dam. The Idukki arch dam doesn't have any shutter. Only in Cheruthoni dam, there is an outlet for releasing the water to the Periyar river.
The Cheruthoni dam has five shutters. The shutter at the centre is opened first. Then one shutter each on the left and right sides will be opened. Then two shutters will be opened in the same manner. About 10-15 cm of each shutter is usually opened. All the shutters are operated by electricity.
At 168.91 metres the Idukki reservoir is one of the highest arch dams in Asia. Its construction is so unique that the pressure of the water inside the double curvature dam is eased to both sides.
The dam connects Kuravan and Kurathi hills.
The news of the opening of the Idukki Dam takes us back to the severe floods that occurred in 2018. The dam was then opened amidst heavy rain and imminent floods. After the opening of the dam in 2018, the water level rose by five meters in the Cheruthoni river.
It was after 26 years that the Cheruthoni dam was opened in August 2018. This caused large-scale destruction in the Thadiyampad Causeway and on the banks of the Periyar river. Later on October 26, one of the shutters of the dam was opened after the forecast of heavy rain. Then, the water level in the Cheruthoni river rose by one foot.
The likely path and impact
When the shutter is opened, the water will enter the Cheruthoni river first. It will travel through the spillway and reach Vellakayam where it will merge with the Periyar river. If the Chapathu in Thozhupuzha-Pulliyanmala State Highway is submerged in water, the traffic on the Idukki-Kattappana route will be affected.
Then the water will wind its way through Thadiyampad, Karimpan Causeway, Chelachuvadu, Keerithodu, Plamba forest area, lower Periyar dam, Neriamangalam, Bhoothankettu, Idamalayar, Malayatoor, Kalady, Aluva, Chengamanad, Eloor, Varapuzha, Manjaly and Chendamangalam. This water also goes to areas in western Kochi such as Vallarpadam, Panambukad, Mulavukadu and Ponnarimangalam.
The water will finally enter the sea through the Vembanad Backwaters on one side and through the Kottapuram Backwaters near Kodungalloor on the other side.
The Lower Periyar and Bhoothankettu dams have been already opened.
The Nedumbassery International Airport may be affected if the water level goes up unusually.
