This analysis was made using the default
values in an
UNCALIBRATED landslide risk model. In
a separate study, this model was compared to two other shallow
landslide risk models. SMORPH output correlated most closely
to known landslide patterns in western Washington. Landslide
risk in SMORPH is based largely on the 10 m
DEMs,
i.e., slope and concavity; therefore, this model works well
in situations where topographic factors drive shallow landslides.
SMORPH was found to be less sensitive to initial input variables
than the other models tested and was determined to be more
likely to accommodate greater error in initial condition
selection than the other models tested. Authors of the model
comparison concluded that SMORPH was well suited for a landslide
risk screening tool and that the default input variables
were applicable to the MidCoast Region of Oregon.
Calibration of this model was beyond the scope of this
watershed assessment. However, an advantage of SMORPH
over other models is that mapped landslide inventory data
can be used to easily calibrate and refine this model.
Nevertheless, our initial run should be a close approximation
of the risk due to topographically-driven, shallow landslides.
We used the output from this model to rank 6th Field
Watersheds based on the proportion of their area occupied
by shallow landslide high risk zones. This ranking went
into the
Large
Wood Source Areas multifactor analysis.
A calibrated run of this model can be used to identify
specific areas within the watershed that are prone to
shallow landslides.
This analysis uses an uncalibrated landslide
risk model. If this approach seems useful, landslide inventory
can be collected, in a spatially explicit way, and used
to calibrate this model. Additional information is available
in S. C. Shaw and L. M. Vaugeois. 1999. Comparison of
GIS-based Models of Shallow Landsliding for Application
to Watershed Management. WA DNR, Timber Fish & Wildlife
Report TFW-PR10-99-001.
Spreadsheet Data: smorph_summary.xls
Shapefile: smorph-6thfield.zip
(430K)
&
smorph.zip
(12MB; this is the output grid file)
Metadata: MD_smorph_by_6th_field.doc
Click to Enlarge
Avg: 27.6% of watershed area in High Risk
Max: 41.3% of watershed area in High Risk
Min: 1.2% of watershed area in High Risk
Please address questions or comments
to:
Dr. Ralph Garono
Principal Investigator
Earth Design Consultants, Inc.
rgarono@earthdesign.com
Laura Brophy
Principal Investigator
Green Point Consulting
brophyl@peak.org |
homepage 
