As of 8 am Rembau Standard Time on the 22nd August 2020, the 3 Gorges Dam water level was at 167.65 m or about 7.35 m away from the design limit of 175 m. The 5th flood peak of the Yangtze River has passed through the 3 Gorges dam but China is not out of danger anytime soon.
We have a prototype dashboard obtainable from here.
The number one issue facing China right now will be the water level at the 3 Gorges Dam. During the 5th Flood Peak which started on Tuesday and ended on early Saturday morning, the water level of the 3 Gorges Dam was raised from 158.4 m to 167.65 m, for a total net change of 9.25 m. The 3 Gorges Dam started the week with about 16.7 billion tonnes of water retention capacity and ended the week with only 9.2 billion tonnes left.
Crucially however, China has bought itself some time as the latest reading indicates inflows at 42,100 m3/s and outflows at 48,600 m3/s, for a net discharge of 5,500 m3/s. This has the effect of lowering the water level of the 3 Gorges dam by approximately 35 mm/Hr, if the dam continues to discharge at 48,600 m3/s.
There are several effects we would like to go through in this post.
No 1 Earthquake Risk
The point to note is that there are numerous yellow dots which represent numerous seismic events within the 3 Gorges Dam reservoir . The earthquake risk is an existential risk of the 3 Gorges Dam, that was known prior to its construction but ignored.
The first is the increased earthquake risk posed by retaining the additional amount of water as part of the 3 Gorges dam flood prevention measure. Currently, the additional water accumulated behind the dam arising from the No 5 flood which occurred this week was about 6.8 billion tonnes. If we add an assumption that the water carried 10% weight by volume of debris, the total additional weight pressing on the tectonic plates.
The above diagram has been adapted from an excellent paper on the seismology of the 3 Gorges Dam area. The key thing to note is that the 3 Gorges dam, the purple triangle, is situated near many fault lines and near the Zigue Basin anticline and the Huangling anticline. The point to note is the 3 Gorges dam itself i.e. the structure is not the important point because a vast area actually forms the reservoir. So the yellow dots which represent the various seismic events detected all can be said to be have occurred within the 3 Gorges dam reservoir. The point to note is that there are numerous yellow dots, numerous seismic events – the earthquake risk is an existential risk of the 3 Gorges Dam, that was known prior to its construction but ignored.
No 2 Misleading information
If you read the media, there is a frequent mention that the 3 Gorges dam maximum discharge capacity is at under 50,000 m3/s. That is simply not true, the maximum discharge capacity of the 3 Gorges Dam is 100,000 m3/s. So it is discharging at 50% of maximum capacity. We can only speculate as to why the 3 Gorges Dam is not discharging near the peak capacity, given that impounding so much water behind the 3 Gorges dam increases the earthquake risk.
No 3 Weather Outlook
Finally, the Yangtze River basin will experience mild weather over the next 24 – 48 hours. This can hopefully give some time for the 3 Gorges dam to complete its discharge. However, discharging quickly raises earthquake risk as the tectonic plates are not compressible springs that expand and contract as we choose. They store potential energy and the expansion could lead to a seismic event – hopefully it does not.