A Tributary of the Mighty Skagit

The USGS DEM was interesting in that it encouraged upper Finney Creek to flow into Deer Creek. A single pixel was tweaked to restore the original flow.

Extensive fractal analysis was done on this area. The results were written up by Anicet Beauvais in ...


Calculating slope and contributing area involves important decisions. Aside from the bag of worms of scale dependency, there are many algorithms vying for our attention. For the most part, we are content with the ARC/INFO implementation of a bi-quartic surface fit through a point and it's eight neighbors. However, this is is inappropriate for calculating a stream slope from a DEM. (Of course, the best stream slopes involve the calculation of intercepts of mapped streams with contour lines.)

The next image shows the slope from any given river cell to its lowest neighbor. (This is a good place to compare dithered and approximated colors. Netscape users see Options:Preferences:Images and Security.)

The next image shows the slope of the river between junctions, derived by querying the DEM for the elevation at each junction, and dividing the distance by the stream length.

Grain Size

Grain size is proposed to be function of slope and contributing area. Below is a plot of D50, the modeled grain size, for Finney Creek. We used the junction-to-junction slope and the ARCINFO/TOPMODEL all-the-water-in-a-cell-flows-to-the-lowest-of-its-eight-neighbors algorithm for contributing area. The constants were derived from field work at the site.