Understanding Dam Failure

Oct 23 2013

Dams are potentially destructive structures. As a barrier that obstructs large quantities of flowing water or slows the movement of water to create a lake or reservoir, there is a huge risk in destruction of populations and the environment if a dam fails. Utter dam failure is not very common, but when it does happen the damage is immense. To put this in perspective, one dam failure in China in 1975 killed one hundred and seventy one thousand people and destroyed the homes of some eleven million people. This was the Banqiao Dam disaster that is widely considered to be the most catastrophic dam failure in history. But what causes these kinds of disastrous breaches to occur in the first place?

 

What Causes Dam Failure?

Most dams don’t entirely impede the flow of water. Many dams are built to generate hydroelectric power and feature spillways to allow water to pour through either intermittently or constantly. Even dams that are not used for hydroelectric power have spillways. The spillway design, however, is one way in which dams fail. This may involve poor construction in terms of both techniques and materials. In general, just about anything could cause a dam to fail. Everything from environmental factors like weather to human caused failures like engineering flaws or neglect can reasonably lead to dam failure.

Geologic factors are a huge part of dam construction and maintenance. This is especially true when surveying a location for a dam and filling it. Changes to water levels can lead to dam failure at any stage, but is particularly common during filling. Geologic factors like landslides due to seismic activity can cause the reservoir to spill over the dam and weaken the structure enough to cause it to collapse. A serious earthquake is always a serious risk to the integrity of a dam. If the earthquake is large enough, it can disrupt the entire dam system and cause a complete failure.

Erosion of the surrounding landscape can also lead to an eventual dam failure. This is notable involving earthen dams that are constructed directly from the surrounding landscape. Of course, despite the many natural factors that can lead to dam failure, human error is a major contributor as well. Poor maintenance of the internal dam systems such as outlet pipes, spillways, and computer systems have caused numerous dam failures throughout history. The likelihood of complete dam failure can increase when one of these design factors combines with a natural occurrence. A poorly maintained system or engineering flaw in the dam combined with heavy rains, causing flood conditions and a weakening of the foundation is a devastating mix for dam failure.

Improvements in dam surveying, placement, and engineering have reduced severe dam failures, but they do still occur. Usually, a combination of heavy rains, flooding, and some structural deficiency lead to dam failures. While issues regarding dam design integrity can be constantly adjusted and reevaluated, nothing can be done to prevent heavy rains.

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