My perpetual map of the Bill Williams River, AZ is squeaking toward a state of preliminarity. The story of the BWR is a fascinating one. It is a large, sediment laden river with a fantastically skewed flood regime (i.e. flood peaks that are orders of magnitude larger than average flows) that has been bottled up by a dam with a tiny peak-release capacity since 1968. Thus, its potentially huge, but short-lived flood peaks (spikes of 50 to 150+k cfs) have been degraded to long-lived, low discharge events (bricks with prolonged peaks of no more than 7k cfs) that have lots of time to impart change to the channel. Since the dam traps easily more than 95 percent of the river's load, lots of interesting things happen.
The mapping that I have been working on is an attempt to document the morphological change in the river corridor over the last 60 years or so with a nice set of orthorectified aerial images from each decade. Lots of cool things can be done with the images, mapping, and GIS. So far, I have only mapped each generation and 'cookie-cut' them into each subsequent generation to illustrate the evolving mosaic of alluvial deposits. This is made quite simple with the analysis\overlay\erase and data\general\merge functions in ArcGIS. A much more elaborate scheme using the analysis\overlay\symmetrical difference tool is also in the works. Instead of the straight cookie-cutter approach, the sym difference approach essentially piles each layer on the other and then cookie-cuts it, creating a sort of virtual stratigraphy that documents what features have changed to what features (or have remained the same) over the time series.
In any case, the series of images above provides some visual insight into how a dynamic fluvial system evolves and creates the complex mosaic of deposits and surfaces that you see at any given time. In this case, the final map is the net result of only 5 decades of activity. Ahh...surficial geology...so simple, right? Soon the maps will have legends, etc. Just wanted to show some real progress. The image below shows how individual surfaces from each generation remain out there today in an intricate array.
