In a major dam related disaster at around 10.50 pm on Aug 10, 2024[i], one of the crest gates at the Tungabhadra dam has broken[ii] near Hospete in Vijayanagara district in Karnataka, causing the release of 70,000 to 100,000 cusecs of stored water. The chain on the 19th (of total 33 gates) gate of Tungabhadra dam on Tungabhadra river, part of Krishna River Basin, got cut, snapped and was washed away about 100 m from the dam on Saturday. The chain that was used to operate the gate snapped as the welding gave way. The Tungabhadra gates only have chain and not chain and rope as in some other dams. 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. This possibly happened due to heavy flows, but also due to wear and tear of over 70 years of operation of the dam. A temporary stop log gate is now being planned, as permanent crest gate will take time.
The disaster raises a number of questions about the operation and maintenance of the dam.
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.
Karnataka deputy Chief Minister D K Shivakumar admitted to media on Aug 12 while visiting the dam that there were danger sings at the Tungabhadra Reservoir. Repair work can be started only after release of about 60-65 TMC (Thousand Million Cubic Feet) out of storage of 105 TMC of water from the dam, but it will take several days to do so. Approximately 20 feet of water needs to be drained before repair work can begin. A technical team from Chennai and Andhra Pradesh is expected to arrive soon[iii]. The dam was commissioned in 1953. According to the latest information, the preliminary repair work may have started. Efforts are focused on repairing the gate with water levels at 1,625 feet, aiming to conserve as much water as possible.
Tungabhadra dam is one of India’s largest stone masonry dam and the only non-cement dam besides Kerala’s Mullaperiyar Dam. Both were constructed using surki mortar, which is mixture of limestone and mud. (https://www.theweek.in/news/india/2024/08/11/how-did-tungabhadra-dams-19th-gate-break-flood-alert-as-35000-cusec-water-released.html)
A statement issued by the secretary of the dam said that all maintenance works were completed in May 2024 and that the gates were operated and checked. “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 22890 Cusecs. 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[iv]. According to reports, the dam’s gates underwent comprehensive maintenance in May 2024, including the application of Cardium compound, greasing, and oil filling in gearbox units. Officials had confirmed the gates were in proper working order following these procedures. However, there is no word from National or State Dam Safety Authorities if either of them had inspected and given certificate of safety before the monsoon. Will the NDSA show promptness to inquire into the disaster the way they did for Medigadda dam disaster in Telangana?
After a meeting with MLAs, MPs, and TB Board experts, it is expected that 2,00,000 to 3,00,000 cusecs of water will be released into the river, opening all 33 gates of the dam. The full discharge capacity of the dam is 6.5 lakh cusecs. A high alert has been issued for the districts of Ballari, Koppal, Hospete/ Vijayanagara, Raichur in Karnataka and Kurnool in Andhra Pradesh.[v] The downstream Rajollibanda and Sunkesula barrages, with flood design capacities of 7.65 lakh cusecs and 2.08 lakh cusecs respectively, are expected to handle the flow without issue[vi].
The Andhra Pradesh State Disaster Management Authority asked people along the Krishna bank to be careful[vii]. “People in Kurnool district’s Kosiri, Mantralayam, Nandavaram and Kouthalam should exercise caution,” said APSDMA managing director R Kurmanadh.
The statutory interstate body Tungabhadra Board has initiated action to fabricate a new stop log gate. The process is being overseen by gate works expert Kannaih Naidu, who has submitted the necessary designs and drawings. Fabrication discussions are ongoing with the involvement of dam authorities, the Managing Director of Karnataka Neeravari Nigam Limited (KNNL), and the Secretary of the Tungabhadra Board[viii]. The official Tungabhadra Board website, however, has no information about the disaster as on Aug 11 2024. Its Twitter[ix] site also has no information about this incident.
According to the official Tungabhadra Board’s website (see the screenshot above), the water level at the dam in the morning of Aug 11 2024 was 1632.6 ft, almost same as its Full Reservoir Level of 1633 ft. With monsoon only less than half way through, why was the dam filled up to FRL? It seems this is neither safe, nor in accordance with the rule curve. In last ten days, as we can see from the following graph from the official Tungabhadra Board website, there was sufficient time and opportunity to reduce the water level at the dam by maintaining the outlfows of Aug 1/2, but the out flows were reduced and opportunity lost.
According to one report[x], in a similar incident in the past, a gate on left bank upper level canal had broken and the technical team found it difficult to repair the same.
The Karnataka deputy Chief Minister announced on Aug 12 that a committee of experts will be formed to assess the structural safety of state’s dams, after visiting each such dam.
Will there be any credible independent inquiry to find out the answers to questions raised here and others? So that right lessons are learnt and such incidents are avoided in future?
SANDRP (ht.sandrp@gmail.com)
POST SCRIPT:
POST SCRIPT 2: Engineers and experts began work on fixing a temporary crest gate at the Tungabhadra Dam here on Aug 14 2024. Four metal sheets, each weighing 10 tonnes, were brought to the dam using heavy-duty cranes. Three more heavy-duty cranes and five more steel sheets will reach the dam on Thursday. The engineers and experts said that they would complete the installation work within three days.
(https://www.newindianexpress.com/states/karnataka/2024/Aug/15/engineers-begin-fixing-temporary-crest-gate-at-tungabhadra-dam-karnataka Aug 15 2024))
POST SCRIPT 3: Sept 6 2024: The Tungabhadra Board has constituted a committee of experts to find out the reason for the collapse of 19th crest gate of the Tungabhadra dam on Aug 10 2024. The expert panel is headed by Shri A K Bajaj, former chairman of CWC and includes Harkesh Kumar, Tarapuram Sudhakar and representatives of technical consultative committees of Karnataka, Andhra Pradesh and Telangana . The committee will examine whether the gate and chain links were inspected from time to time and also assess the safety of other crest gates of the dam. (https://www.deccanherald.com/india/karnataka/panel-of-experts-to-probe-tb-dam-crest-gate-collapse-3179018)
References:
[i] https://www.deccanchronicle.com/southern-states/andhra-pradesh/tungabhadra-dam-gate-washes-away-emergency-response-underway-1815589
[ii] https://x.com/navin_ankampali/status/1822410488229277776
[iii] https://x.com/navin_ankampali/status/1822453311871582336, 7.30 am, Aug 11
[iv] https://indianexpress.com/article/cities/bangalore/flood-threat-karnataka-tungabhadra-dam-crest-gate-washed-away-9507678/
[v] https://x.com/TweetzBallari/status/1822457637880905857/photo/1
[vi] https://www.deccanherald.com/india/karnataka/tungabhadra-dam-gate-snaps-causing-sudden-outflow-of-35000-cusec-water-into-the-river-3145992
[vii] https://timesofindia.indiatimes.com/city/bengaluru/karnatakas-tungabhadra-dam-gate-washed-away-after-releasing-floodwater-downstream/articleshow/112439335.cms
[viii] https://tbboard.gov.in/
[ix] https://twitter.com/TB_Board
[x] https://www.udayavani.com/english-news/tungabhadra-dam-gate-chain-snaps-massive-water-flow-into-river-basin-causes-panic
SANDRP 
TMC unit is 1000 million cft not cubic meter
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Yes, already corrected.
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Thanks
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