India ranks as the third-largest builder of large dams globally, with over 5,300 operational dams storing water for irrigation, hydroelectricity, and municipal use. However, structural failure of a dam wall releases massive hydrostatic heads, generating high-velocity flood waves that cause severe downstream loss of life, infrastructure destruction, and long-term ecological damage.

Key Causes of Dam Failures

• 1. Overtopping Due to Inadequate Spillway Capacity:
  • Extreme hydrometeorological events, cloudbursts, or sudden reservoir inflows that exceed design spillway discharge capacity cause water to spill over the crest of the dam. In earthen embankment dams, overtopping leads to rapid erosion and wall breaches.
• 2. Foundation and Geotechnical Instabilities:
  • Internal seepage, piping (erosion of core material through foundation soil), and chemical dissolution of subsurface strata cause foundational shifts, undermining structural stability.
• 3. Material Fatigue and Aging Infrastructure:
  • Age-related deterioration—such as concrete alkali-aggregate reactions, spillway gate corrosion, and cracking in older masonry—weakens dam integrity. UN reports indicate that hundreds of large Indian dams are over 50 years old.
• 4. Seismic and Tectonic Activity:
  • Ground motion along active fault lines can induce reservoir-triggered seismicity (RTS), fracture concrete arches, and cause liquefaction in embankment foundations.
• 5. Operational and Sluice Gate Failures:
  • Mechanical failures in emergency spillway gates, delayed water release, or communication breakdowns during flash floods prevent timely reservoir drawdowns, escalating structural pressure.
• 6. Reservoir Siltation:
  • Silt accumulation reduces live storage capacity, forcing dams to fill rapidly during early storm events and raising overtopping risks.

Two Examples of Large Dam Failures

1. Machchhu-II Dam Failure (Morbi, Gujarat – 1979)

• The Disaster: Following intense rainfall (over 600 mm in 24 hours), reservoir inflows reached nearly three times the design spillway capacity.
• The Breach & Impact: Floodwaters overtopped the earthen flanking embankments, causing the dam wall to disintegrate. A 4-meter wall of water swept into the downstream industrial city of Morbi within minutes, causing thousands of casualties and widespread destruction.

2. Banqiao Dam Failure (Henan Province, China – 1975)

• The Disaster: Super Typhoon Nina produced unprecedented rainfall, exceeding the 1-in-1,000-year hydrological forecast.
• The Breach & Impact: Sediment-choked sluice gates could not discharge the volume, causing the clay-core embankment to overtop and fail. The resulting flood wave triggered the cascading collapse of 61 downstream dams, causing massive loss of life and displacing millions.

Institutional Measures in India

• Enacted the Dam Safety Act, 2021, establishing the National Committee on Dam Safety (NCDS) and State Dam Safety Organisations (SDSOs) to mandate periodic structural audits and Emergency Action Plans (EAPs).
• The Dam Rehabilitation and Improvement Project (DRIP), supported by the World Bank, funds structural rehabilitation and early warning telemetry across aging dams.

Preventing dam failures requires combining real-time hydrometeorological forecasting with structural audits and downstream evacuation plans to protect lives.