Of late, the Cheruthoni dam, whose spillways are discharging up to 8 lakh litres of water per second, has been stealing the thunder and the Idukki arch dam has been momentarily consigned to oblivion. In early 1983, I was posted at Idukki as project-in-charge of the dam monitoring section after undergoing training at Montreal, as part of the transfer of technology programme between Canada and India under CIDA (Canadian International Development Agency), which aided the whole project.
The Idukki and the other two dams, still in their infancy (commissioned in 1975), were constantly monitored through a cluster of embedded instrumentation, pendulums etc. Idukki is Asia’s first double-curvature thin-shell parabolic arch dam. The Canadian consultants, who assisted in designing and supervision, had executed a bigger multiple arch dam, the Daniel-Johnson dam (702 ft high and five times Idukki dam’s volume) in Canada.
The Idukki dam’s statistics and features are astounding. Almost 555 ft high with double curvature like an inverted egg shell segment, it is known for its phenomenal strength. By arch action, the huge thrust from the water is transmitted to the natural abutments viz. Kuravan and Kurathi Mala (hillocks). The volume of concrete consumed by the arch dam is only 4.5 lakh m3. Had Idukki been a gravity dam—where the thrust of water is resisted by the sheer weight of the dam—it would have consumed about four to five times the volume of concrete. (For example, the 450-ft high Cheruthoni gravity dam consumed 17 lakh m3 of concrete).
For inspection, three galleries have been provided—at 1,900 ft, 2,100 ft and 2,300 ft. They are connected through inclined galleries with steps at both ends. The lift for gaining access to the galleries travels 500 ft (around 50 floors) through a shaft driven in Kurathi Mala. It was then one of the tallest lifts in India.
A frightening incident is still etched in my memory; while descending with VIPs, the lift suddenly got stuck midway. I had to climb all the way up the rung ladder to the machine room and bring the lift safely up.
The call of duty demanded our presence for hours each day inside galleries, which are dimly lit, cold, eerily silent and lonely. Mind you, a few meters away, 2,000 million cubic metres of water is thrusting against the dam body. For the next five years or so the galleries of Idukki, Cheruthoni and Kulamavu dams were my second home. To sum up, I can confidently state that the KSEB dams are built to last.