Dam Safety

Tamil Nadu: Thalavanur check dam collapsed twice within a year

Thalavanur check dam collapsed[i] in morning hours of November 9, 2021. This is the second time the check dam has faced significant damages within a year of its construction. Before this, the same check dam broke down in January, 2021. The first collapse took place 5 months after its inauguration on September 19, 2020. Its construction was started in April 2019.

The Rs 25.35 crore check dam was built across Thenpennai river at Thalavanur in Tamil Nadu. The 650 metres long and 3 metres high structure was sandwiched between Cuddalore and Villupuram districts. It had 6 outlets 3 in Enathimangalam on the Cuddalore side and 3 in Thalavanur on the Villupuram side. Located about 10 km from Villupuram, the check dam was designed to trap flood waters and help recharge ground water.

On January 23, 2021, one of two pillars on the left side of check dam supporting the shutters broke off causing flash floods in irrigation channels. As per Public Works Department (PWD) the newly constructed check dam had reached its storage capacity and soil erosion on the Cuddalore side caused cracks beneath its structure resulting in the damages.

EPS January 25, 2021 image shows damaged portion of Thalavanur check dam.

As per another report, the check dam was overflowing for past 3 months. Due to excessive flow the soil beneath the check dam loosened leading to its collapse. Following the incident farmers had staged protest[ii] raising question on quality of its construction. It was later repaired[iii] at a cost of Rs. 7 crore.

On November 9 2021, the right-side sluice of the check dam collapsed making it useless for the objective it was built. The exact causes of its failure are not known. The government planned to revamp[iv] the entire structure at a cost of Rs 15 crore. However, within a week, the revenue officials demolished the entire structure on November 15.

Express Nov. 10, 2021 image shows the broken right-side sluice of Thalavanur check dam.

As per report, the river had been eroding its bank fast near the damaged portions after water released from upstream Santhanur dam[v] on November 13. To prevent any untoward incident, the official blasted the check dam with explosives.

Google Earth image showing Sathanur dam which is located about 90 km upstream of Thalavanur Check Dam, Viluppuram, Enathimangalam and Cuddalore

The river continued to erode[vi] its bank even after razing of the structure. On November 26, a 3 year old government higher secondary school building in Villupuram faced erosion threat. The 100 families living behind the building were also at flood risk.

Nov. 27, 2021 image by Express shows Thenpennai river eroded its bank up to 50 meters downstream Thalavanur check dam into a govt higher secondary school in Villupuram.
Google Earth image showing government school building and human habitation behind the building which faced erosion threat after collapse of Thalavanur check dam.

The Thalavanur check dam collapse is latest incident of how ill planned and poorly constructed such water structures are falling down wasting public money. Similar concerns have been raised after collapse of Anakkatii check dam[vii] in Tamil Nadu recently. There have been several such incidents particularly in south Indian states which require more attention.

Still, governments in these states especially in Telangana and Tamil Nadu have been planning and building scores of check dams on seasonal and perennial rivers. It is worth mentioning that the Telangana government in March 2021 has decided to build 1,250 check dams[viii] at estimated cost of Rs 4,200 crore and government in Tamil Nadu only last week has proposed to construct 3 more check dams[ix] on Cooum river and cost of 2 of these structures would be around Rs. 12.6 crore.

Left Oct. 27, 2021 and Right Dec. 21, 2021 Sentinel images of Thalavanur check dam.

These plans exclude ensuring safety of construction & operation; dam specific; cumulative impacts on hydrological cycle and river eco-system. It’s time the efficacy, cost-benefits of existing check dams in these states are audited and examined independently.

Bhim Singh Rawat (bhim.sandrp@gmail.com)

POST SCRIPT:- Thalavanur dam demolition bid fails On Sunday (Nov. 14, 2021), officials began the demolition process but the structure across Thenpennai river could not be brought down as the explosives used were weak. Collector D Mohan, who inspected the sluices, said the dam will be demolished to stop further erosion of the river banks and prevent water from flooding nearby villages.

When a sluice gate on the left side of the dam broke in January 2021. It was not repaired immediately as the elections were around the corner and a new government took over in May. In August, officials said a proposal to reconstruct the dam has been sent to the State government and has not been approved yet.

Due to monsoon rains, another sluice in the right side was damaged on Tuesday (Nov. 9, 2021) after the Saathanur dam in Tiruvannamalai district opened shutters recently. The river bank near the damaged right sluice eroded as the inflow from Saathanur dam was increased to 3,300 cusecs on Saturday (Nov. 13, 2021). It took a mere 8-9 hours for the river bank to erode after water was released from Saathanur dam. Hence, explosives were used to demolish the dam, but the efforts were in vain as the structure could not be brought down. https://www.newindianexpress.com/states/tamil-nadu/2021/nov/15/tamil-nadu-thalavanur-dam-demolition-bid-fails-2383672.html  (15 Nov. 2021)


[i] https://indianexpress.com/article/cities/chennai/tamil-nadu-rains-check-dam-in-villupuram-breaks-down-for-second-time-in-a-year-7615233/

[ii] https://www.newindianexpress.com/states/tamil-nadu/2021/jan/25/villupuramabsence-of-officials-at-damaged-check-dam-spot-stirs-rage-among-public-2254613.html

[iii] https://www.thehindu.com/news/national/tamil-nadu/check-dam-damaged-reconstruction-work-begins-near-villupuram/article33648454.ece

[iv] https://www.newindianexpress.com/states/tamil-nadu/2021/nov/10/one-year-into-construction-thalavanur-check-dams-second-sluice-collapses-2381655.html

[v] https://timesofindia.indiatimes.com/city/chennai/newly-built-rs-25crore-check-dam-demolished-in-tamil-nadu/articleshow/87720865.cms

[vi] https://www.newindianexpress.com/states/tamil-nadu/2021/nov/27/thenpennais-fury-at-their-doorstep-100-families-fret-2388662.html

[vii] https://weather.com/en-IN/india/news/news/2021-12-15-environment-activists-question-poor-construction-of-anakkatii-dam

[viii] https://telanganatoday.com/1250-check-dams-to-be-built-in-telangana-harish-rao

[ix] https://www.thehindu.com/news/cities/chennai/three-more-check-dams-proposed-across-cooum/article37981794.ece

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