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.
download fullbasin.ps
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 below 4.
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 buffers.ps
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.
download buffers_b.ps
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%	
runout.aml