Uttam Kumar Reddy inspects Medigadda barrage; officials explain events that led to sinking of piers

Hyderabad: A loud sound similar to a small bomb exploding was heard on October 21, 2023, when Pier no 19, 20 and 21 of Block 7 on the left bank of Medigadda barrage (Lakshmi Barrage) sunk in, said government officials of the irrigation department in the PowerPoint presentation at the barrage on Friday. The dam is shrinking, was one of the damning observations made by the officials on the present condition of the barrage and the damage it has sustained.

T Jeevan Reddy, member of the Legislative Assembly alleged that there is huge corruption in Kaleshwaram project. The cost of the Kaleshwaram Irrigation project so far is Rs 93,000 crores spent to irrigate 98,000 acres of land.

The Congress government along with its water and drainage minister Uttam Kumar Reddy, minister Sridhar Babu, ministers Komatireddy Venkat Reddy, Ponnam Prabhakar, Ponguleti Srinivas Reddy and other leaders inspected the Medigadda barrage, a part of the prestigious Kaleshwaram Irrigation project.

In the PowerPoint presentation, the irrigation officials gave a chronology of the events on the discovery of the damage:

Medigadda barrage:

- The field engineers of the irrigation department rushed to the site at 6:20 pm on October 21 after they heard a loud sound. They noticed damages to Pier no 19,20, and 21.

- The official saw that Pier no 20 and adjacent piers of 18, 19, and 21 have sunk, and the slabs and parapet wall resting on Pier no 20 have also sunk which also affected piers 19 and 21.

- The officials inspected the site at 11 pm and carried out works to avoid further damage including draining the water in the barrage.

- The sinking was stabilised by October 24 and the final settlement was at 1.256 m.

As per the Telangana government, they have carried out the stability works.

- The barrage was designed as an RCC raft duly following the IS Code 6966-Part 1 (1989) and the CBIP manual. Pressure Relief Valves were also provided as a drainage arrangement to relieve the uplift pressure.

- There is a need for revision of the apron design which was already being contemplated by the department.

- Detailed model studies have been done jointly with IIT Hyderabad. Due to continuous rains in the basin and flows in the barrage, an opportunity to implement the modification was not available for the last three years.

National Dam Safety Authority report

The NDSA report on the damages sustained by the barrage was released on November 4. In the report, the NDSA asked the Telangana State to undertake a detailed investigation to determine the causes of failure. It listed issues from the planning, design, quality control, operation and maintenance (O&M) stages that led to the damage. The NDSA asked the government to keep it informed about the outcome of the investigation and the proposed rehabilitation process.

Damage to the road

Later, the road that connects Medigadda barrage to Maharashtra also saw damage. The road bridge panels and parapet wall from Pier no 21 to Pier no 16 sunk. The damage assessment of the road includes:

- Visible cracks on the surface of the bridge road and parapet wall

- A major crack at Pier no 20. The crack width was varying from 150 mm to 250 mm.

- The origin of the crack was not visible as it was underwater and extended above about 5 m from the water level.

- A hairline crack on Pier no 19 and 21.

- A slow whirling action of water on Pier no 20 upstream.

- Two sand boils are noticed between Pier no 16 and 17 and between Pier no 17 and 18.

- Two welding joints between Pier no 19 and 21 were distorted.

- A reverberating sound was heard by officials in the logs resting on Pier no 20 and 21.

After assessing the entire situation, the conclusions drawn by the department are:

- The problem of settlement doesn’t appear to be caused due to any structural failures.

- The differential settlement leading to visible cracks in the pier may be due to sand undermining the raft.

- The cut-off seepage length provided is also sufficient for a safe exit gradient as per design.

- Possible mud/bentonite pockets might have been created while laying cut-offs which may have later opened up gradually or deviation from vertical inclination of piling may lead to gaps between plain and RCC cut-offs leading to a sand migration channel.

Observations by dam safety panel

The report by AB Pandya, chairman of the dam safety review panel and his team, stated that there is structural and seepage failure at the barrage.

- Maximum settlement is at upstream Pier no 20 of 1,256 mm

- Settlement of blocks is visible with the naked eye

- Pier no 20 has serious a structural crack and it extends from the top to the junction and the raft.

The raft has sagged between Pier no 17 and 22 and there is a deep sag at Pier no 20 where twisting and torsion were observed.

Recommendations given to the irrigation department are:

- Take undisturbed samples of the foundation materials and test them for permeability as well as particle size distribution.

- Efficacy of the existing pile cut offs to withstand the scours and their ability to control flows below the barrage needs to be established.

- Structural competence of each component and their assemblage into the barrage units needs to be verified for the various operational conditions.

The way forward proposed by the NDSA was:

- Survey all piers and rafts.

- Survey blocks 6, 7 and 8 immediately.

- Inspection of apron/plinth connection downstream and upstream must be done urgently to know the gravity of damage.

- Plan repair and remedial measures.

- Cracks must be monitored through standard methods of the construction protocols.

Kaleshwaram project costs and pending bills

The cost of the Kaleshwaram Irrigation project so far is Rs 93,000 crores spent to irrigate 98,000 acres of land. The pending bills on the project are approximately Rs 8,000 to Rs 9,000 crores according to the presentation given by the Congress government.