I read in Tweeter (so it is not very good source) that one of the problem of the 3GD is cavitation inside discharge tubes. Cavitation is happening when the speed of the waterflow is above 10 meter per second and water creates “vacuum bubbles” which later collapse and create shockwaves which are able to destroy even strongest materials. The discharge channels are inside the body of the dam as we can see on photos and if there will be a problem, they will affect the dam from inside without overtoping. Obviously, such channels could be closed but this will slow water release and increase chances of the use of the emergency spillway. Such spillway itself could be fragile (like in the case of Oroville dam) and could undermine the dam if damaged.
I read in Tweeter (so it is not very good source) that one of the problem of the 3GD is cavitation inside discharge tubes. Cavitation is happening when the speed of the waterflow is above 10 meter per second and water creates “vacuum bubbles” which later collapse and create shockwaves which are able to destroy even strongest materials. The discharge channels are inside the body of the dam as we can see on photos and if there will be a problem, they will affect the dam from inside without overtoping. Obviously, such channels could be closed but this will slow water release and increase chances of the use of the emergency spillway. Such spillway itself could be fragile (like in the case of Oroville dam) and could undermine the dam if damaged.