A series of simulations of slope stability based a digital elevation model

This 7.5' quadrangle came to us from Peerless Management Systems [This page was created before the USGS had published many 10-meter DEMs.] as contour lines (from the USGS topo sheet) and as a 10-meter DEM. It was slightly cropped for our work. We modified the DEM (as we modify all DEMs) by filling sinks and by incrementing cells by one-millimeter so that water would know how to flow off flat spots.

We applied our own algorithm and C program to calculate contributing area. This information is brought into ARC/INFO® format, and subsequent modeling is implemented through aml (arc macro language) files. The following images show critical rainfall (the amount of steady-state rain in mm/day) necessary to destabilize a slope. Soil cohesion (principally provided by roots) varies from 0 to 8 kilonewtons/mē in the three images.




We can set rainfall to a constant 100 mm/day, and examine the critical cohesion of each landscape element. We start with the original DEM, and then degrade it to a cell size of 30, 60, 90, and 120 meters by averaging elevations.