Flooding along the Tanana River is a common occurrence for those of us who live in Interior Alaska. Normally, the flooding reaches its peak in the spring, as the ice breaks up and occasionally creates ice jams, as shown in the photo.
But, once in a while, summer or fall rain will bring the water level high enough to initiate flooding. As the Tanana River drains the massive Tanana Valley, heavy rainfall can contribute greatly and quickly to a rise of water. The National Weather Service currently (updated 9/23/12) has a flood warning out for the Nenana River starting at its mouth off of the Tanana River. The post discusses the heavy rainfall contributing to unseasonal high water.
The flood of 2008 that affected the Salcha area was probably most present for me, personally. I had friends in Salcha that evacuated due to the high water levels. The Wikipedia article has a pretty thorough play-by-play of the flood, what caused it, how quickly it happened, as well as the long-term consequences of it. I had friends whose home was severely damaged by the flooding in Salcha, so this hit close to home for me. New flood risk maps for the Fairbanks North Star Borough are in development and will be reviewed this week.