Dam failures

Figure 1. The amount of water held back by a dam makes their failure catastrophic.

A dam failure is simply an uncontrolled release of water from a hydroelectric reservoir through a hydroelectric dam as a result of structural failures or deficiencies in the dam. Dam failures can range from fairly minor to catastrophic, and can possibly harm human life and property downstream from the failure.

Dams failures can be extremely harmful, especially because dams are considered "installations containing dangerous forces" under International Humanitarian law. This is because of the immense destruction that can occur with a dam breach. Throughout history, a large number of dam failures have caused immense property damage when floodwaters destroy infrastructure. In addition to these property damages, ecosystems and habitats are destroyed as a result of waters flooding them. Along with this, dam failures over the years have taken thoussands of lives. The older that dams get, the more potential exists for catastrophic dam failures.

Causes

There are four major causes of dam failures, they include:

• Overtopping: These failures occur as a result of poor spillway design, leading to a reservoir filling too high with water, especially in times of heavy rainfall. Other causes of this type of failure include settling of the crest of the dam or spillway blockage. This type of failure accounts for about 34% of dam failures.
• Foundation defects: These failures occur as a result of settlement in the foundation of the dam, instability of slopes surrounding the dam, uplift pressures, and seepage around the foundation. All of these failures result in structural instability and potential dam failure. These defects account for 30% of all dam failures.
• Piping and seepage failures: These failures occur as a result of internal erosion caused by seepage and erosion along hydraulic structures such as the spillways. As well, erosion as a result of animal burrows and cracks in the dam structure contribute to these failures. This type of failure accounts for about 20% of all dam failures.
• Conduit and valve failure: These failures occur as a result of problems with values and conduits. These types of failures account for 10% of all failures.

Other dam failures arise as a result of other miscellaneous causes. Many dam failures are also secondary results of other natural disasters such as earthquakes, landslides, extreme storms, or heavy snowmelt. Other causes include equipment malfunction, structural damage, and sabotage.

Notable Failures

There have been many dam failures throughout history all around the world that have resulted in varying amounts of damage to property. As well, when dams fail the number of deaths and injuries vary drastically. The list of examples below is not comprehensive, but rather serves as an indicator for how dams can fail and how these failures can cause damage.

Banqiao Dam

Figure 2. The Banqiao dam after failure.

The Banqiao Reservoir Dam in the Henan province of China failed in 1975, killing an estimated 171 000 people (although some reports suggest the number could be as high as 230 000). When the dam failed, it destroyed the homes of 11 million people and is considered the largest dam failure in history.

In August 1975, the region experienced an extreme flood, resulting in quantities of water falling that had not been considered during the construction of the dam. More than a years worth of rain fell in only 24 hours, and the dam failed on August 8. Early on August 8, the dam was breached and 700 million cubic meters of floodwater was released, flooding communities and homes downstream. After this burst a chain reaction began, and the other 61 reservoirs located in the area collapsed releasing another six billion cubic meters of floodwater. The water covered an area equal to 10 000 square kilometers. The failure to plan and account for extreme floodwaters resulted in the immediate death of 26 000 as a result of the water itself. 145 000 more people died as a result of epidemics and famine following the flood.

Sayano–Shushenskaya Dam

A turbine in the Sayano–Shushenskaya dam in Khakassia, Russia broke apart violently on August 17, 2009, causing significant damage. The turbine hall and engine room flooded, destroying 9 of the 10 turbines and collapsing the ceiling of the turbine hall. A total of 75 people were killed. This led to significant power failures in the local area.

The cause of the incident was reported to be unsafe vibrations coming from one of the turbines, which caused the turbine to break apart violently. Water that had been entering the turbine flooded the turbine hall, flooding the room and levels below. The ceiling of the hall also broke apart from impact from the turbine. At this point, power failed in the power station resulting in a blackout. Steel gates to the water intake pipes of the turbines were manually closed and spillways were opened to prevent more damage.

Teton Dam

Figure 3. The reservoir emptying through the Teton dam.

The Tenton dam near Idaho Falls failed completely on June 5, 1976, releasing the contents of its reservoir. This failure began with a large leak near the right abutment of the dam. The dam failed just as it was being completed and filled for the first time. After the first leak was noticed, a wet spot developed on the face of the dam from seepage coming in from the abutment rock. Material began to slough off and erosion continued on the embankment. The water escaping increased as the hole grew and attempts to fill the hole failed. The dam breached when the crest of the embankment fell and a wall of water surfed through. 40% of the dam embankment was lost, and the powerhouse was completely submurged in debris. It released nearly 400,000 cubic meters of water, then flooded farmland and towns downstream with the eventual loss of 14 lives, directly or indirectly, and with a cost estimated to be nearly $1 billion.