Slope Stability in upper Big Elk Creek basin
Here are results of an investigation of slope stability on Big Elk Creek,
east of Newport Oregon.
The shalstab model (Montgomery/Dietrich) was run on the entire Big Elk Creek
basin, down to it's outlet into the Yaquina River. The model assumptions
were cohesion = 2 kiolPascals (typical for logged slopes), phi = 33°,
bulk density of dry soil = 2.0, soil depth = 1 meter. A value of
Q/T = -2.8 corresponds to a steady-state rainfall of 100mm day.
Analysis was based 30-meter DEMs.
The streams selected for intensive study are shown in the east.
Areas with Q/T < -2.8 are assumed to be unstable after logging. They are
shown in yellow and red. Shallow landslides originating in these areas are
assumed to travel downhill until the slope (measured between two cells) drops
NOTE: For a brief time, we had posted results based a runout threshhold
of 4% instead of 4°. That data was labeled as based on 4%
download zipped all28.e00 file for the cover
(select stream buffers with "resel all28 poly INSIDE eq 100", unstable
areas with "resel all28 poly GRID-CODE eq 50", and runout paths with
"resel all28 poly GRID-CODE eq 100".)
download zipped lbuffers.gra for this image
This is a simplified version of the previous map.
Upper watershed: 39729920 square meters
NMFS buffers: 10713207 27%
log(Q/T) sq meters sq meters sq meters
threshhold unstable + runout +buffers
-2.7 3509100 8.8%
-2.8 2612700 6.6% 5420700 13.6% 13598960 34.2%
-2.9 1779300 4.5%
-3.0 1209600 3.0%
-3.1 792900 2.0%
-3.2 531900 1.3%