Cheruthoni Dam, Gravity dam in Kerala, India

Cheruthoni Dam is a gravity dam on the Periyar River in Kerala, India, standing 138 meters high and creating a reservoir among forested valleys. The concrete barrier follows a curved line across the riverbed and stores water that flows through pressure shafts to underground power stations.

Construction began in 1969 and finished in 1976 as part of a large hydroelectric project to meet growing power needs in Kerala. The works required the relocation of entire village communities whose lands were submerged.

The name Cheruthoni derives from Malayalam words referring to the smaller sister in a three-dam system across this mountainous region. Local farmers watch the water levels closely, as they shape irrigation plans during the rainy season and dry months.

The site is open daily, but permissions are needed to take photographs or approach certain restricted areas more closely. Access follows roads that wind through tea plantations and forested patches.

Cheruthoni holds the spillway for the whole Idukki reservoir, so all surplus water from the three-dam system leaves through its five radial gates. They were first fully raised on 10 August 2018, when inflow kept rising after the first gate opened and the level passed 2,400 ft, sending 750 cumecs down the Periyar.