Dams have existed for various reasons like water supply, flood control, power generation, recreation, and navigation. When we think about dam safety issue, we can easily realized that it is not an issue of conflicts or interests of each party, but an issue of preventing crucial disaster when dam fails. Therefore, what we call, “conflicts” is not matters of whether we take actions to ensure dam safety or not, but things about optimum method among numerous reinforcing, remediation ways, economic evaluation, client’s need, etc.
Here is one recent vivid example in China earthquake, 2008. According to the relatively recent news shown in the “The Australian”, 5/16/2008, hundreds of thousands of survivors of China's devastating earthquake were facing a new threat of inundation from collapsed dams. At that time, two thousand soldiers were deployed late to plug cracks in the Zipingpu dam, upriver from the earthquake-stricken town of Dujiangyan, in Sichuan province, which is home to 600,000 residents. Tulong dam, further north on the Min river, was said by officials to be near collapse, something that would have a knock-on effect on a series of dams and power stations downstream. Dujiangyan would be swamped if the dam failed. Authorities admitted the earthquake had damaged 391 dams and some were in danger of bursting. (http://www.theaustralian.news.com.au/story/0,25197,23705080-2703,00.html)
Number of Dams in California: 1495Number of State Regulated Dams: 1255
Number of High Hazard Potential Dams: 462
ASDSO classified 3 different level of dam hazard in California, which is “high-hazard potential dam”, “Significant-hazard potential dam”, and “low-hazard potential dam”, and various efforts have been taken and planned now.
As we can see the above article, dam safety issue should never be negligibly treated. Federal and Statewide efforts must be taken to prevent any disastrous failure. Here on this page, general dam safety problems relating failure mechanisms are described. Later, promising solutions and measures are introduced in detail.
Dam Safety Problems (Failure Sources)
Overtopping
- due to heavy flows or inadequate spillway capacity or discharge capacity
Seismic Issues by Earthquake
- Liquefaction (flow failure, slump, lateral spreading)
- Earthquake damages causes every kinds of other problems such as cracking, seepage through cracks, settlements, landslides, damage to outlet works, fault rupture, etc)
Seepage and Piping
- This is an issue within a dam body or within a foundation, or along the interfaces
- The importance of consideration of seepage through embankment dams is highlighted by statistics.
Among records for more than 11,000 embankment dams, 136 or 1.2% of dams had failed. Of the failures, 59, or about 44% were caused by seepage and piping.
Landslides and Slope Instability
- Landslides can affect abutments or outlet/discharge works
- It affects water quality
- Slope should be specially cared during the end of construction, first filling, rapid drawdown, steady state seepage, and earthquake.
Cracking
Differential Settlement
Burrowing Animals and Vegetation
These are the main problems that induce dam instability and failure. In addition to the above, erosion, wave action, dissolutioning of water soluble materials, deterioration of rock formations can be harmful to the dam safety. The promising solutions for these focus on the four main mechanisms among many sources: Overtopping, Seismic, Landslides, Seepage and Piping.
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