Engineering Disasters - Dams Disasters

A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundments. Most dams have a section called a spillway or weir over or through which water flows, either intermittently or continuously, and some have hydroelectric power generation systems installed.

Dams are considered "installations containing dangerous forces" under International Humanitarian Law due to the massive impact of a possible destruction on the civilian population and the environment. Dam failures are comparatively rare, but can cause immense damage and loss of life when they occur. In 1975 the failure of the Banqiao Reservoir Dam and other dams in Henan Province, China caused more casualties than any other dam failure in history. The disaster killed an estimated 171,000 people[1] and 11 million people lost their homes.
A notable case of deliberate dam failure (prior to the Humanitarian Law rulings) was the British Royal Air Force Dambusters raid on Germany in World War II (codenamed "Operation Chastise"), in which three German dams were selected to be breached in order to impact on German infrastructure and manufacturing and power capabilities deriving from the Ruhr and Eder rivers. This raid later became the basis for several films.

Other cases include the Chinese bombing of multiple dams during Typhoon Nina (1975) in an attempt to drain them before their reservoirs overflowed. The typhoon produced what is now considered a 1-in-2000 years flood, which few if any of these dams were designed to survive.

Common causes of dam failure include:

Sub-standard construction materials/techniques (Gleno Dam)
Spillway design error (South Fork Dam, near failure of Glen Canyon Dam)
Geological instability caused by changes to water levels during filling or poor surveying (Malpasset Dam).
Sliding of a mountain into the reservoir (Vajont Dam – not exactly a dam failure, but caused nearly the entire volume of said reservoir to be displaced and overtop the dam)
Poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava dam collapse)
Extreme inflow (Shakidor Dam)
Human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant)
Internal erosion or piping, especially in earthen dams (Teton Dam)
Earthquakes