With video:

...At Valleyfair Amusement Park, parking lots are flooded and the roller coaster is partially underwater.The Minnesota River is expected to crest Thursday.

http://www.keyc.com/node/35273

I went last year for the first time to Vallyfair. Park was Dead in the middle of July. From the looks of it looked like Renegade was under water. Wasnt to really impressed with the coaster when I rode it.

so what happens after a flood, at amusement parks. What sort of work must be done to a wood coaster? steel? flat rides?

It depends. At parks like Coney Island of Ohio and Six Flags Over Georgia and Knoebel's Amusement Resort, flooding is relatively frequent and the rides and attractions are designed with this in mind. The Great American Scream Machine, a wooden coaster at Six Flags Over Georgia, for instance, was designed knowing that the area it is in frequently floods. Of course, debris must be cleared, areas cleaned, etc. Knoebels, in particular, is known for quickly recovering from floods.