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A flood alert has been sounded downstream of the Tungabhadra dam in Karnataka’s Koppal district after one of the 33 crest gates of the massive stone masonry dam across the Tungabhadra river was washed away late on Saturday evening (August 10).
Repairs can be carried out only after two-thirds of the dam is emptied, the Tungabhadra Board, which manages the project, said. Karnataka Deputy Chief Minister D K Shivakumar, who is also the Water Resources Minister, visited the dam on Sunday.
How the gate broke
The dam has 33 ‘vertical lift’ type gates that move on rollers embedded in the masonry. The gates are operated from an overhead bridge.
“On 10.08.2024, 10 spillway gates were operated, i.e. from gate No. 12 to 21 to height of 1.5 feet and the discharge through the spillway gate was 22,890 Cusecs,” the Tungabhadra Board said in a statement on Sunday. Spillways or overflow channels are structures used for the controlled release of water from a reservoir.
“During the said incident, i.e., at 10.50 pm, the spillway gate No. 19 was washed away from the groove of spillway,” the statement said.
The crest (or spillway) gate failed after a link in the chain used to operate it broke. The force of the water in the dam swept the 60-foot-by-20-foot gate, weighing around 20 tonnes, some 500 ft away, J Purushottham, president of the Tungabhadra Farmers’Association, said.
Local sources said welding was carried out on the chain links of the spillway gates to strengthen them 3-4 years ago. Purushottham said that considering the chain links were old, Karnataka had suggested that the links be replaced with steel cables to operate the crest gates. “Such a system is in place in the Alamatti dam in Bagalkot district,” he said.
Water in reservoir
On August 10, the reservoir level was at its maximum 1,633 ft, and the dam was full to its capacity, about 105.8 thousand million cubic (TMC) ft, according to Tungabhadra Board data. The inflow was 40,925 cusecs (cubic ft per second), and outflow was 28,133 cusecs.
According to the Tungabhadra Board statement issued by its Secretary O R K Reddy, following early inflows into the dam, water had been released through three gates on July 22 and, as inflows increased subsequently, around 1.65 lakh cusecs was released on August 1.
On Monday, the water level was almost 1,631 ft, and the reservoir capacity was 97.75 TMC ft, Board data show.
Accumulated silt over the years now fills around 30 % of the original capacity of the dam. The state government has proposed to build a balancing reservoir to address this problem.
River and the dam
The Tungabhadra, which is formed at the confluence near Shimoga of two streams, Tunga and Bhadra, that rise in the Western Ghats, flows into the Krishna at Sangamaleshwaram in Andhra Pradesh. The river, which forms part of the boundary between Karnataka and Andhra Pradesh, has a total catchment area of almost 70,000 sq km.
The Tungabhadra reservoir sprawls over an area of 378 sq km primarily in Karnataka’s Vijayanagar district. It is one of the major reservoirs in South India that supplies water for irrigation and industrial use, as well as drinking water to Karnataka and Andhra Pradesh.
The dam was first conceived of in 1860 to mitigate the impact of recurrent famine in Rayalaseema. Construction was begun by the erstwhile governments of Hyderabad and Madras in 1945, and the project was completed in 1953.
The Tungabhadra Board was established by a presidential order in 1953. The Board currently has a chairman appointed by the Union government, and four members, representing the Union government and the states of Karnataka, Andhra Pradesh, and Telangana.
Repairs and fears
The crest gate that has been swept away is located in the middle of the dam, and repairs can begin only after 60-65% of the water in the reservoir has been discharged.
The repair will be carried out as soon as possible with consultation with experts, the Tungabhadra Board has said. “Action is being taken to fabricate new stop lock gate… The…work will be completed within a week,” the Board said.
Cultivators with fields upstream are afraid that draining of the reservoir to carry out repairs will impact irrigation; those downstream have the same fear, apart from apprehensions of flooding due to increased outflows from the dam. The Karnataka State Natural Disaster Monitoring Centre has issued a flood alert to downstream areas.
Heavy rainfall could make the situation worse; however, no heavy rain is forecast in the region in the coming days.
Last year, due to a severe drought in the state, farmers either did not get the yield they hoped for, or avoided sowing altogether. Shivakumar said a projected inflow of around 50-60 TMC ft in September and October would help farmers in the region cultivate at least one crop this year.
