Three Gorges Dam
Posted: Wed 25 Aug 2004, 06:54:27The Virginina posted this in a different thread:
I visited the dam site a couple of years ago and seen a lot of what is there, both upstream and downstream. The first link above is partial fact. The second link is just male bovine excrement with most of the posts displaying total ignorance of the project.
So, what did I find?
1. There is a risk with this, as in any major energy project. In this case, the risk is aggravated because the Yangtze flows through the gorges which were formed by a seismic fault. No earthquakes of > Richter 5 have ever been measured in the region and the dam is built for Richter 6+, so there is theoretically an order of magnitude of safety built in.
2. Water is incompressible, so that the shockwave of an upstream earthquake hitting the dam may be more disastrous than an earthquake at the dam site itself.
3. It is impossible to calculate the effect of an extra 60 billion tonnes of water on the seismic balance and this weight may be sufficient to trigger an earthquake.
4. The gorges themselves are formed from mainly friable sedimentary rocks. There are many places where it is evident that enormous chunks of mountain have, in recent geological history, broken off and fallen into the river. In fact, I witnessed a small landslide (I have photos). A large one could cause a surge wave which could overflow the dam and probably cause it to rupture.
5. Two large HE dams about 100 km N of the site burst in the latter half of the 20th c. (I can't remember the exact date) causing the death of an estimated 250,000 persons (official figure is 75,000), due to weather conditions causing an overflow. These were also correctly built and engineered dams.
6. The city of Yichang is ~20 km downstream from the dam, with a population of ~ 2 million. If the dam burst or overflowed, for any reason, the population would be wiped out. Wuhan is a major city (>7 million) 100 km or so downstream. Some of the population there could be evacuated. Jingzhou (6 million) is halfway between these, but not on the Yangtze, although in its flood plain. My guess is that a burst would kill >10 million in Hubei Province alone.
7. There is another risk, totally unrelated to a dam burst. China's largest city is Chongqing with a population of 31 million. Its sewage flows, untreated, into the fast-flowing Yangtze, where it decomposes rapidly aerobically. It is at the head of the retention lake. As the river slows down, the sewage will fall to the bottom as organic silt and it is estimated that a layer some 10 m thick will form in the gorges within a decade. This will decompose anaerobically, forming vast amounts of methane gas. Some of this will bubble up harmlessly (except that methane is a bad greenhouse gas causing climate change). Experts have stated that the pressure of 180 m of water above it will cause it to crust before decomposition is complete, forming vast reservoirs of methane which will grow and eventually burst. If this happens near a town, such as Wushan, on a calm day, a gigantic explosion could occur, as the humid gas would be held in by the gorge walls, rather than spread out. Where you have habitations, you have sources of ignition. At the best, the river will become very smelly from the quantity of raw human waste stagnating in the dam lake, probably with disease-bearing organisms. It should be remembered that the cities like Wushan have been rebuilt from current river levels to form a new shoreline 180 m higher.
I'm not mentioning the catastrophic human, agricultural, cultural and archaeological issues resulting from this terrible construction.
I visited the dam site a couple of years ago and seen a lot of what is there, both upstream and downstream. The first link above is partial fact. The second link is just male bovine excrement with most of the posts displaying total ignorance of the project.
So, what did I find?
1. There is a risk with this, as in any major energy project. In this case, the risk is aggravated because the Yangtze flows through the gorges which were formed by a seismic fault. No earthquakes of > Richter 5 have ever been measured in the region and the dam is built for Richter 6+, so there is theoretically an order of magnitude of safety built in.
2. Water is incompressible, so that the shockwave of an upstream earthquake hitting the dam may be more disastrous than an earthquake at the dam site itself.
3. It is impossible to calculate the effect of an extra 60 billion tonnes of water on the seismic balance and this weight may be sufficient to trigger an earthquake.
4. The gorges themselves are formed from mainly friable sedimentary rocks. There are many places where it is evident that enormous chunks of mountain have, in recent geological history, broken off and fallen into the river. In fact, I witnessed a small landslide (I have photos). A large one could cause a surge wave which could overflow the dam and probably cause it to rupture.
5. Two large HE dams about 100 km N of the site burst in the latter half of the 20th c. (I can't remember the exact date) causing the death of an estimated 250,000 persons (official figure is 75,000), due to weather conditions causing an overflow. These were also correctly built and engineered dams.
6. The city of Yichang is ~20 km downstream from the dam, with a population of ~ 2 million. If the dam burst or overflowed, for any reason, the population would be wiped out. Wuhan is a major city (>7 million) 100 km or so downstream. Some of the population there could be evacuated. Jingzhou (6 million) is halfway between these, but not on the Yangtze, although in its flood plain. My guess is that a burst would kill >10 million in Hubei Province alone.
7. There is another risk, totally unrelated to a dam burst. China's largest city is Chongqing with a population of 31 million. Its sewage flows, untreated, into the fast-flowing Yangtze, where it decomposes rapidly aerobically. It is at the head of the retention lake. As the river slows down, the sewage will fall to the bottom as organic silt and it is estimated that a layer some 10 m thick will form in the gorges within a decade. This will decompose anaerobically, forming vast amounts of methane gas. Some of this will bubble up harmlessly (except that methane is a bad greenhouse gas causing climate change). Experts have stated that the pressure of 180 m of water above it will cause it to crust before decomposition is complete, forming vast reservoirs of methane which will grow and eventually burst. If this happens near a town, such as Wushan, on a calm day, a gigantic explosion could occur, as the humid gas would be held in by the gorge walls, rather than spread out. Where you have habitations, you have sources of ignition. At the best, the river will become very smelly from the quantity of raw human waste stagnating in the dam lake, probably with disease-bearing organisms. It should be remembered that the cities like Wushan have been rebuilt from current river levels to form a new shoreline 180 m higher.
I'm not mentioning the catastrophic human, agricultural, cultural and archaeological issues resulting from this terrible construction.
