For only the third time since the Idukki dams system in Kerala was commissioned in 1975, one of the five shutters at Cheruthoni was opened Thursday (the earlier occasions were in 1981 and 1992) after water in the reservoir rose to 2,399.04 ft, precariously close to its full storage level of 2,403 ft. Even after a discharge of 50 cubic metres per second, the reservoir has continued to rise, and the discharge will be increased to 100 cubic metres per second from 7 am Friday.
Rain and reservoir
The lake sprawls across Kerala’s lifeline Periyar river, and was created by the arch dam of Idukki, and the smaller Cheruthoni and Kulamavu dams. Incessant rain since the onset of the monsoon has left Idukki and other reservoirs downstream brimming. While Kerala as a whole has received 15% excess rain, Idukki district got 41% excess until August 8.
Full and overflowing
The Idukki arch dam has no shutters. The Kulamavu dam has penstock pipes that carry water to an underground power station at Moolamattam 43 km away. The water from the reservoir is used to run six generators with a total installed capacity of 780 MW.
Shutters of Cheruthoni dam are opened when the dam reaches full reservoir level. At Panamkutty downstream from Cheruthoni, a tributary of the Periyar called Mudirapuzhayar joins the flow from the dam. At Kallarkutty on the Mudirapuzhayar stands a power generation dam with a storage of 457 ft above sea level — this dam is currently overflowing, boosting the flow in the Periyar. A little ahead stands the Lower Periyar dam, which, too, is overflowing.
Further on its journey towards the sea, the Periyar is joined by a tributary called Edamalayar, which has a dam by the same name. The shutters of Edamalayar dam were opened Thursday. Next along the route is the Bhoothathankettu dam in Ernakulam district. The Periyar then winds its way through Kalady and Aluva on the last leg of its journey to drain into the Arabian Sea 24 km north of Kochi. Another branch of the river flows from Aluva to Kochi’s Udyogamandal before merging with the backwaters.
Threat to Kochi airport
In its journey to the sea, the Periyar comes within 2 km of Kochi’s international airport, the runway of which was built after reclaiming a paddy field. A stream called Chengalthodu drains water from the airport into the Periyar. When the Edamalayar dam was opened in 2013, water had flooded the runway; fears that the rising Periyar would also lift the Chengalthodu led to operations at the airport being suspended temporarily Thursday afternoon.
A first this monsoon
On both earlier occasions, the Idukki dam was opened in October, during the northeast monsoon. This is the first southwest monsoon that has seen the dam being opened, and when the Edamalayar dam too, has been opened.