Sounds to me you possibly have conflicting mods. Check if you have no other disaster mods active. I have seen the flooding disaster 2 times already and it always properly stops after a short time.

I don't have any other disaster mods. I think this mod might have lost track of the fact that it's supposed to stop flooding.

I am running into the same issue. My cities is flooded. I have added many large water pumps around the city hoping it would get rid of the flood. No luck. My cities pumps 4.2 m3/week, but only demands 432K m3/week. I don't have any mods turned on related to disasters. Any suggestions? Other than starting over?

Hard to say what to do about it. Did you by chance also experienced vehicles that get stuck and when clicked upon give a wrong description? T.b.h. I think the game engine is just being overloaded but when this occurs is different for everyone. I am experiencing the vehicles problem around 20k of people. I can remove the stuck vehicles but within an hour or so another vehicle gets stuck causing traffic jams. Seems to happen a lot with cars and trains likely because the number of vehicles of that type is much higher then ships and aircraft.