Little Mountain Slope Stability Modeling
This is a quick slope stability modeling analysis of the slopes of Little
Mountain near Stillman Creek in Lewis County. Imagery is the one-meter NAIP
orthophoto series from the summer of 2006. The 10-meter DEM is a USGS product
derived from the USGS 1:24,000-scale topo sheets. The 3-foot DEM is from
a survey flown last winter by the Puget Sound Lidar Consortium. It is the
first of the Consortium data to be flown at 8 pulses/meter and gridded at this
resolution.
![](topo.png)
detail of USGS Boistfort Peak quadrangle
![](naip.png)
Orthophoto from 2006
![](tenshade.png)
10-meter DEM
![](ten2kp.png)
Critical rainfall: SHALSTAB stability model run on 10-meter DEM,
cohesion = 2 kP
![](lidarshade.png)
LiDAR DEM
![](lidar2kp.png)
Critical rainfall: SHALSTAB stability model run on LiDAR DEM,
cohesion = 2 kP
Following are perspective renderings of the photo and the two stability models:
![](naip3d.png)
![](ten2kp3d.png)
![](lidar2kp3d.png)
and here are model results with cohesion of 4 kiloPascals,
a value closer to the strength before clearcutting.
![](ten4kp.png)
![](lidar4kp.png)
![](ten4kp3d.png)
![](lidar4kp3d.png)
Following are slope maps, created with 2 different sets of class breaks.
![](slope10m.png)
![](slopelidar.png)
![](slope10m2.png)
![](slopelidar2.png)
Following are results of the simple version of SHALSTAB, using no cohesion, but increasing the friction angle to compensate.
![](ten45.png)
![](lidar45.png)
And here is new information, that Harvey got around to assembling
October 2011
![](photo2009.png)
NAIP 2009 orthophoto. This is a four-band image with one-meter pixel size.
![](dnrslides.png)
Landslides as mapped by DNR from the Seattle Times post-storm photo.