The Nazis repaired the Ruhr dams within 6 months I think. Still, it diverted substantial resources from Normandy to do so, which was probably consequential to the success of the D-day invasion.
If we got into a for realz war with China it would be bordering on pointless to attack the TGD if the best we could hope for was disrupting river barge traffic for 6 months. Destroying the power generating infrastructure would be a worthy goal if a full dam breach wasn’t feasible. But even that would only disrupt them for however long it took to get replacement parts for the damaged bits. That could be weeks, or that could be decades depending upon how much other industrial capacity we managed to disrupt.