The first warning was sounded Thursday evening at the Mullaperiyar Dam after the water level reached 136 feet following heavy rains in the Idukki district.
The Tamil Nadu government has informed the Idukki district administration that it will open the spillway shutters at 10 am on Friday.
The average hourly inflow at Mullaperiyar till 7 pm was 6592 cusecs. At present, the average discharge is 1912 cusecs.
Meanwhile, the shutters of Malampuzha Dam, which is the second largest in Kerala, will most likely be raised by 9 am on Friday in the wake of heavy rains received in the catchment area.
By 6 pm on Thursday, the water level in the dam was 112.06m. The rule curve of 112.99m is likely to be breached in the prevailing rain situation, informed the District Information Office, Palakkad.
Those residing along the Bharathapuzha, Mukkaipuzha and Kalpathy Puzha have been advised to exercise caution and not venture into the water bodies for fishing and other activities.
At present, five relief camps are operational in three taluks -- Chittur, Mannarkkad and Alathur -- in the Palakkad district.
Last month, the spillway shutters of the Malampuzha Dam had been raised by 30 cm to release excess water.