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Another 3 Gorges image that has been floating around. It is notably missing an honest caveat from the original post on Reddit. I don't want to beat the person up. They made it clear they did not want to be deceptive, but I want to discuss the map.
@Gurdur @evolutionarypsy
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@Gurdur @evolutionarypsy
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This is one of the missing caveats: "The map only considered 2 main factors: Terrain and Distance to the main stream of Yangtze River. But, Condition of weather, up stream and tributary rivers and man-made facilities…weren’t take into account. Therefore, ..."
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"...this can only be viewed as an amateur map, not really a professional assessment."
There are many things wrong with the map, but I applaud candor.
Breach modeling was done for the dam. I guarantee it. But I can find it nowhere. I suspect this person was honestly curious.
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There are many things wrong with the map, but I applaud candor.
Breach modeling was done for the dam. I guarantee it. But I can find it nowhere. I suspect this person was honestly curious.
/3
The first context I saw this in was describing a 100 m wall of water going downstream should the dam fail. This entails Faulty Fundamental assumption 1: the dam just suddenly disappears.
Aside from the specifics of just how *humongous* this dam is, dams fail in increments.
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Aside from the specifics of just how *humongous* this dam is, dams fail in increments.
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"Humongous" - it's not height. Yes, it's pretty tall, but pales compared with JinPing 1 (305 m, 1000 ft) and only ranks 73 worldwide in existing dams for height
It's all the concrete and generating capacity that make it rather stunning. It's not just going to fall over. /5
It's all the concrete and generating capacity that make it rather stunning. It's not just going to fall over. /5
Most of it you can't even see because its under water.
Back to the image.
I did some calculations from the DTM (digital terrain model) in Google Earth and am pretty sure based on measurements and the creator's caveat that they assumed it was a 100 m wall of water ...
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Back to the image.
I did some calculations from the DTM (digital terrain model) in Google Earth and am pretty sure based on measurements and the creator's caveat that they assumed it was a 100 m wall of water ...
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...that would persist all the way or most of the way downstream. That doesn't happen. The height of a peak is attenuated as it moves downstream. Energy losses mostly from friction. It flattens out. Faulty Fundamental assumption 2: the (hypothetical) wave doesn't flatten.
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Another thing is that sediment, rocks, debris also dissipate energy as the wave works on moving them downstream.
Imagine this effect by picturing what would happen if you dump a bucket of water in a gutter and then if you dump it in a gutter with sediment and leaves in it.
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Imagine this effect by picturing what would happen if you dump a bucket of water in a gutter and then if you dump it in a gutter with sediment and leaves in it.
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Faulty Fundamental assumption 3: there are no downstream controls.
I can't beat the author up for this. He says that it neglects man-made structures (i.e., he was relying only on a low resolution DTM).
The Yangtze has always been a flooding problem.
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I can't beat the author up for this. He says that it neglects man-made structures (i.e., he was relying only on a low resolution DTM).
The Yangtze has always been a flooding problem.
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There are all kinds of levees, bulkheads etc to control flows (mainly in cities). Now, levees are generally fairly fragile. If they overtop, they tend to erode and breach in places. For example, the Mississippi overtops levees with fair regularity, flooding towns & farmland.
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There are other more esoteric issues such as temporal factors, tributary inflows, floodplain behavior, and how to deal with the ocean.
I may post some things on why 3 Gorges sucks, just to be fair.
Nuff said. Don't get excited about that image.
/end
I may post some things on why 3 Gorges sucks, just to be fair.
Nuff said. Don't get excited about that image.
/end
