My thought is that they blew a dam downstream to lower tail-water at the 3G dam.
2 water levels to keep in mind, head water (the high side of the dam) and tail water (low side of the dam). If the tailwater gets too high, then the delta between the headwater and tailwater is smaller and reduces the flow of water through the dam. Not usually an issue for the spillway since it pours over top of a gated area higher up on the dam, but the water flow through the hydroelectric plant is reduced as the tailwater rises relative to the outlets where the water through the plant exits.
From an electrical standpoint, high tailwater reduces the output of the dam and if it’s too high, there isn’t enough delta between headwater and tailwater to operate the plant. If that happens, they shut down units and NO water flows through the plant, relying only on the spillways.
Given the amount of water they need to move, they need all the flow through the dam that they can get. If tailwater was so high that they couldn’t operate the generating plant, they would only have the spillways to rely on for flow. That might be the reason that they allegedly blew a dam downstream - to lower tailwater so that 3G could utilize the path through the plant as well as the spillway for water movement.
covering the Orville Dam Spillway collapse.
Hopefully he'll do a segment on Three Gorges soon.
7
Makes sense. Sounds like with your level of understanding you’ll appreciate these photos and analysis, if you haven’t seen them:
https://www.taiwannews.com.tw/en/news/3965733