https://journal.probeinternational.org/three-gorges-probe/who-is-behind-chinas-three-gorges-dam/
The wild card is if a large landslide, caused by one of the frequent earthquakes in the area, caused a tsunami-like effect in the water behind the dam.
Chinese construction was faulted by the European commission that was asked to investigate - they were kicked out. The Dam rests against the canyon walls and is not anchored to them. Chinese concrete is notoriously poor in order to skim money off the construction costs - often cardboard is used as a filler, some times plaster.