“Dams are vital infrastructure designed to retain large bodies of water, crucial for irrigation, flood control, and hydroelectric power generation. Ensuring dam safety goes beyond the structural integrity of their massive concrete forms. It encompasses preventing cracks and scouring both upstream and downstream. While the public often focuses on the solidity of these imposing structures, the critical role of hydro-mechanical equipment cannot be overlooked. These components, such as gates and valves, are essential for managing water flow and maintaining the dam’s stability. If these mechanisms fail or operate inadequately, these can jeopardize the entire structure. The safe and efficient operation of gates is particularly pivotal, since malfunctioning of gates can lead to unpredictable stress and strain patterns within the dam, potentially compromising its integrity and safety.”
This statement encapsulates the multidimensional aspects of dam safety, emphasizing both structural robustness and the pivotal role of operational equipment.
Analysis of various dam failures reveals that the majority of these incidents are primarily due to inefficiencies in the operation of hydro-mechanical equipment. Key components such as gates, valves, and turbines are crucial for controlling water flow and ensuring the structural integrity of dams. Malfunctions, such as faulty gates or slow response times, have frequently led to catastrophic outcomes. Additionally, poor maintenance, aging infrastructure, and human error exacerbate these risks. Hence, while structural stability is crucial, the reliable and responsive operation of hydro-mechanical equipment is equally, if not more, vital for preventing disasters and ensuring public safety. The total loss to the government due to this failure is estimated to be around Rs1,000 crore (approximately $120 million).
Background
Teesta Dam is part of the Teesta-V power station (510MW), located on the Teesta River in the Indian state of Sikkim. The dam serves multiple purposes, including hydroelectric power generation, irrigation, and flood control.
The incident at Teesta Dam
The failure occurred at 01:42 Hrs on 4th October 2023. The region experienced an unprecedented Short Duration High-Intensity Rainfall (SDHR) followed by an outburst of Lhonak Lake, leading to a sudden and massive inflow of water into the Teesta basin, which overtopped the entire dam body. The dam gates could not be operated in time to release the excess water, leading to overtopping and structural damage to the dam.
Causes
Delayed gate operation was a significant factor, as the gates could not be opened promptly when the water levels began to rise rapidly. There were potential malfunctions or delays in the automated gate control systems, or a lack of real-time decision-making support. Additionally, there were communication failures, including inadequate or delayed weather forecasting and inflow prediction, which did not provide sufficient warning to the dam operators. Poor coordination between meteorological agencies, dam operators, and disaster management authorities further exacerbated the situation.
Consequences
The incident led to massive downstream flooding, causing extensive damage to infrastructure, homes, and agriculture. There were reports of loss of life and injuries to residents in the affected areas The disaster also affected over 25,000 people, leading to the loss of lives, damage to homes, and the washing away of several bridges and roads. Furthermore, military equipment, including firearms and explosives, were swept away by the floodwaters, leading to additional losses. The economic impact was significant, with substantial losses due to damage to property, disruption of power supply, and agricultural losses.
Impact on hydro-mechanical equipment
The spillway gates, designed to control the release of excess water, were severely damaged. The sudden and massive influx of water rendered the gates inoperable. Structural deformation and mechanical failure of the gates occurred due to the high forces exerted by the floodwaters and debris, likely exacerbated by the impact of boulders and stoplog units that fell on the radial gate arms and cylinders during the dam’s overtopping. It is notable that ten stoplog units, which were in a dogged condition at the top of the dam, were washed away during the overtopping event.
The intake gates, which regulate water flow into the power generation system, could not be closed, and intake tunnels were blocked by debris and sediment carried by the flood. The mechanical systems controlling the gates were damaged, preventing proper operation and leading to further complications in managing the water flow.
Impact on the dam structure
The dam’s foundation and embankments were eroded by the intense floodwaters. The downstream face of the dam suffered significant scouring. The concrete structures of the dam, including the spillway and retaining walls, experienced cracking and spalling (breaking into smaller pieces) due to the impact force of the water and debris. Additionally, access roads, bridges, and other auxiliary structures supporting the dam and its operations were washed away, hindering rescue and repair efforts.
To provide a precise account of the damage and outline a timeline for restoration, below is a detailed assessment based on the Teesta Dam failure incident in 2023 due to a Glacial Lake Outburst Flood (GLOF):
Tentative damage assessment
Hydromechanical equipment:
The spillway gates, including all five radial gates, two sets of stoplogs, hydraulic hoists, gantry crane, embedded parts, glacis liners, and other associated equipment, were completely washed away or damaged beyond repair.
The silt flushing gates had all hydraulic cylinders, power packs, and control panels submerged and now require replacement or extensive repairs.
The intake gates suffered blockages from debris, damage to the mechanical system, and structural damage to the hoist.
Dam structure:
The foundation and embankments experienced erosion, scouring, and compromised structural integrity.
Concrete structures of the dam, including cracking, spalling, and sections being washed away.
Auxiliary structures, such as access roads, bridges, support structures, electric installations, vehicles, equipment, and inventories, were completely destroyed or washed away.
Restoration and timeline:
Phase 1: Immediate response (0-3 months): Activities include evacuation and rescue operations, initial damage assessment, temporary stabilization of the dam structure to prevent further collapse, clearing debris, and securing the site. The timeline for this phase is three months.
Phase 2: Detailed assessment and planning (3-6 months): This phase involves a comprehensive structural assessment, planning and design of repair and restoration works, and procurement of necessary materials and equipment. The timeline for this phase is three months.
Phase 3: Structural repairs (6-18 months): Activities during this phase include repairing and reinforcing the dam foundation and embankments, reconstructing damaged concrete structures, and restoring auxiliary structures such as access roads and bridges. The timeline for this phase is twelve months.
Phase 4: Hydro-mechanical equipment and gates repair (18-30 months): This phase focuses on the restoration of spillway and intake gates.
Phase 5: Testing and commissioning (30-36 months): Activities include comprehensive testing of all systems, commissioning of hydroelectric power generation, and final safety inspections and certifications.
The total expected timeline for full restoration is thirty-six months (three years).
Lessons learned following the Teesta dam incident
Importance of timely gate operation: Gates must be operated proactively based on real-time data and predictive models, rather than relying solely on reactive measures. Automated gate systems should be reliable, regularly tested, and equipped with manual override capabilities.
Enhanced forecasting, advance warning system, and communication: Weather forecasting models need improvement to better predict extreme weather events. Developing integrated systems for real-time data sharing between weather agencies, dam operators, and emergency services is crucial.
Regular drills and training: Conducting regular drills and training for dam operators is essential for effective emergency response. Increasing public awareness and preparedness for dam-related emergencies is also necessary.
Infrastructure resilience: Investing in infrastructure upgrades is important to enhance the resilience of dams against extreme weather events. Regular safety audits and maintenance of dam structures and operating systems should be conducted.
Conclusion
The catastrophic damage to the Teesta Dam and its infrastructure following the 2023 GLOF incident demands an urgent and robust response. Restoration efforts must not only focus on the immediate repair and reconstruction but also on enhancing the overall resilience of the dam against future disasters. The recovery plan should be bold, aiming for rapid stabilization and protection of the dam within the first year, followed by phased reconstruction over the next two to three years.
Key actions include immediate emergency measures to prevent further damage, comprehensive structural assessments to identify vulnerabilities, and extensive repairs to both civil and hydro-mechanical systems. The installation of advanced weather forecasting and monitoring systems is essential. These systems must be integrated with real-time data-sharing networks linking meteorological agencies, dam operators, and emergency response teams to prevent such disasters in the future.
By taking these decisive steps, the Teesta Dam can be restored not just to its original capacity but can be transformed into a model of resilience and safety, safeguarding against the growing threat of climate-induced disasters.
