Dam it!

Discuss environmental matters here, and compare notes on what renewable energy systems might be best for you.
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Devil
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Dam it!

Post by Devil »

http://www.bbc.com/news/world-us-canada-38952847

Once more the dangers of dams is illustrated.

http://bnellis.eu/global/glhydro.html
Safety

Large hydroelectric schemes require a risk analysis. It has been estimated that over 250,000 deaths have been attributed to dam accidents since 1950; the exact figures are unknown. The causes have been varied. In the case of large mountain dams, the worst case scenario would be a dam structure bursting; today this would be rare because the dams are monitored by satellite and ground-based laser instrumentation and any minor changes in the anchoring would be detected before a catastrophe occurred. For example, the Tseuzier Dam in Switzerland was temporarily emptied as a precaution because a tunnel was being pierced about 2 km distant. The Malpasset disaster in France was an example of a dam breach. Other disasters due to landslides into the reservoir include the Vajont dam in Italy, where a resultant tsunami overtopped the dam, killing over 2000 people downstream. On a smaller scale, the Mattmark disaster in Switzerland was caused by a massive block of ice, calved off the Allalin glacier, falling into the lake before the dam was finished. Most of the deaths were construction workers for the dam. The worst disaster was on a river dam, the Banqiao dam in China. In reality, three dams were involved and the prime cause was due to a typhoon with a very heavy rainfall and spawned a small tornado which caused the water level to rise over the rim of the dam, which was not itself constructed according to normal safety standards. The resultant wave caused the failure of two other dams downstream on the same river. From direct and indirect causes, it is officially estimated that 171,000 people died as a result but some experts claim the figure was much higher. A Wikipedia article catalogues over 30 dam (not all hydroelectric) failures globally since 2000, although many were without fatalities, so there are many downstream from large dams who may be still at risk.

How safe are existing large dams? It is not easy to answer, because many failures are due to freak weather or other conditions. For example, the Banqiao disaster has been described as a 1-in-1000-year freak. Even if this assessment were valid, there is nothing to stop a similar event occurring tomorrow and then nothing for 2000 years! In my opinion, the biggest potential catastrophe could occur on the Three Gorges Dam if something happened. The dam itself is built close to a seismic fault line but has been built to withstand a magnitude 7 earthquake, so the risk there is low. However, upstream the gorges even overhang the reservoir and an earthquake in known seismic zones could trigger a large rockfall, creating a tsunami. The last time I was in China, I witnessed a small landslide about 30 km west of the dam and this started me thinking about the safety of the project. This could be exacerbated by reservoir induced seismicity (RIS) and experts have published figures that the frequency of seismic events has increased since the reservoir was filled. The level of the reservoir has been dropped in anticipation of increased water inflow from rainstorms upstream of the reservoir; what would have happened if an upstream dam (not built to the same standards) fails? There would be no time to drop the water level. Whoosh! Let's just imagine what would happen if the dam overflowed from whatever cause. The first place to be hit would be Yichang, just 20-odd km downstream, with a population approaching 1 million. There would be no time to evacuate the population. The major city of Wuhan with over 8 million inhabitants, some 200-odd km downstream. In between Yichang and Wuhan, there are tens of smaller communities and much good agricultural land.
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Dominic
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Re: Dam it!

Post by Dominic »

I think places like China have a lot more to worry about than Cyprus. Their actions on the Mekong with regards to damming leave a lot to be desired.

https://www.internationalrivers.org/resources/8477
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Living in Polemi, Cyprus with my wife and daughter.
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