If you’re looking for a good place to start on the Japan Flooding campaign, it looks like the river overtopped its levee here http://www.tomnod.com/campaign/japan_flood_2015/map/4boxhy26 and the debris field spreads east (through the river-side village, you’ll find houses moved whole from wherever they used to be), turns immediately south around the next village that seems up on a slight ridge, then east toward an irrigation canal where it spreads north and especially south. To the south there are whole villages along and near the irrigation canal that are surrounded by water. Eventually you’ll get all the way south to the city of Joso, where the worst of the flood damages seemed to occur.
Some news items about the flood event thus far:
Japan Times http://www.japantoday.com/category/national/view/floods-stretch-limits-of-japans-elaborate-water-networks
BBC (one of the photos here is that location of the levee breach) http://www.bbc.com/news/world-asia-34205873
New Scientist (another excellent photo of levee breach) https://www.newscientist.com/article/dn28165-did-global-warming-play-a-role-in-japans-devastating-floods/
If I could make a suggestion for admins, that might be to make a topographic layer available for the image area. Flood studies almost always start with a topo, some idea of where the breach occurred, and the image. Searching for flood damage is far more efficient that way–just keep going across flats and downhill from the levee breach.