Scaling DEMs and flowdirection

No, this page is not about how measures like slope vary with scale. It describes techniques for scaling DEMs and flowdirection rasters to preserve the maximum hydrological flow information from the high-resolution raster. For example, one might want to use 2-meter or 10-meter DEMs to build 150-meter DEMs and flowdirections for the DHSVM model, or use 3-second DEMs to build 5-minute cells for the VIC model.

DEMs

Information will be added soon.

Flowdirection grids

This sections refers to the ESRI method of encoding a unique flow direction from a grid cell to one of its eight neighbors. Instead of building a course DEM, filling sinks, and calculating a flow direction grid, and it possible to track the high-resolution flow (e.g. of water) over the boundaries of the large cells, and to reflect it in the large cells. The result is a DEM that may not correspond exactly to any DEM, but reflects actual flows with high accuracy.

flowscale.py is internally documented for now. I will add better instructions. I will also build a pushbutton version that incorporates calls to ESRI libraries.

Direction tweaking

One way of tweaking flowdirection grids in arcmap is to
Harvey Greenberg
hgreen@u.washington.edu
University of Washington
Department of Earth and Space Sciences
Box 351310
Seattle WA 98195-1310