A large ammount of water like what you said in a short time can send the fish into "shock" A flash flood flips there enviroment upside down in an instant and quick changes in the enviroment can send the fish running for awhile. Seems like the bigger fish were affected but not the little ones. In my experience, when the fish are in "shock", they hunker donw deep in grass, sit as deep as they can in brush piles ect. Kinda think like if there were a tornado coming for your house. You would get in the most protected area in the middle. So bass are the same way. All the sudden a massive ammount of highly oxygenated water is dumped in and the fast change scares them. Puttin a heavy jig in the grass and brushpiles is probably what you have to do. Throw it in, shake it a few times, then reel in and cast to a different part of the grass or other structure because your basically gonna have to put the jig right on the fish's head. Hope this helps