Identifying Geological Hazards in the Harrop Procter Community Forest Area
INTRODUCTION

Results & Discussion

The goal of this project was to evaluate land characteristics and
identify areas that may require further ground analysis to confirm
susceptibility to geological hazards. For simplicity, the term “landslides” will
be used as a generic term to describe geological hazards.

Both maps suggest further ground analysis may be necessary
to confirm areas of slope instability. This is indicated by the redcolored regions, which suggest that there is a high possibility of
a geological process such as a debris slide occurring. The lower
fuzzy membership value in the Harrop Creek wildfire map is
attributed to the additional burn severity criterion; fewer areas
are potentially instable under the specified parameters.
Nevertheless, both maps reflect some overlap in areas that
may be susceptible to sliding.

Understanding the locations of these potentially sensitive sites may help
in protecting aquatic and terrestrial ecosystems, public safety, community
drinking water, road infrastructure, and economic opportunities. It may
also help in identifying areas where mitigation efforts may reduce the
impacts of geological processes.

There are several headwaters in or near these potentially
sensitive sites that should be noted. Most of these sites connect
to Harrop Creek or Narrows Creek. Additionally, the entire study
area has a proximity to streams less than 1 km. If geological
processes occur, this distance to streams suggests a good
possibility of waterways becoming impacted. Care should be
exercised in assessing these areas to confirm the impacts that
may be felt towards aquatic ecosystems, water intakes, road
infrastructure, and users of the HPCFA.

Criteria for Analysis
Slope, terrain instability, vegetation cover, distance to roads, distance
to streams, and burn severity were all considered in this analysis and were
rated on a scale of 1-5 based on their importance in influencing landslide
susceptibility (Table 1). A value of 1 indicated low susceptibility and a
value of 5 indicated high susceptibility.

Limitations & Assumptions
No standard set of criteria defines the potential occurrence
of a mass wasting event; therefore, assumptions were made on
the criteria used in this analysis based on literature readings and
professional advice. It was assumed that the selected criteria
had some level of influence on slope instability. The extent that
this criteria influenced landslide susceptibility also led to some
assumptions in selecting the Fuzzy Overlay types.
Data that would have been helpful but was absent in this
analysis included drainage density, precipitation patterns,
snowpack, and spatial representations of natural disturbances.

Further Research
This type of analysis
may benefit from
the creation of a
prediction model
built with the
ModelBuilder in
ArcGIS. The model
may then be
applied to other
areas of similar
terrain, wildfire
histories, and
landslide
disturbances.

Methodology
A Fuzzy Overlay analysis was selected for this project due to the
uncertainties involved in landslide susceptibility mapping. Fuzzy Logic
enables complex phenomena with no discrete boundaries to be
modeled by using Spatial Analyst tools that consider potential data
inaccuracies. Data was first converted into a raster format, then
quantified using the Euclidean Distance Spatial Analyst Tool and the
Reclassify Spatial Analyst Tool. Each criterion was then ranked and
reclassified using manual breaks to reflect the weighted criteria in Table 1.
The Fuzzy Membership Spatial
Analyst Tool was then applied to
each layer (Table 2); this
classified each factor into a
common scale of 0-1 in which 0
indicated a low possibility and 1
indicated a high possibility (of an
occurrence).
Each fuzzy membership layer was then combined using the Fuzzy
Overlay Spatial Analyst Tool to generate a final surface. On the HPCFA
map, slope, terrain instability, and vegetation cover were combined with
the “Fuzzy AND” overlay type, then combined with the distance to roads
and distance to streams layers using the “Fuzzy PRODUCT” overlay type.
On the map considering the Harrop Creek wildfire, this process was
repeated except the burn severity layer was incorporated into the criteria
in which the “Fuzzy AND” overlay type was used.

Acknowledgements
I would like to express my sincere gratitude to the following people for offering their time, ideas,
insight, assistance, feedback, and/or support in this project:
Erik Leslie, Tom Bradley, Sarah Crookshanks, Tedd Robertson, Gavin Fox, Brendan Wilson, Tracey
Harvey, Keyes Lessard, Carol Andrews, Allison Lutz, Rena Vandenbos, and William Burt.
IEP 271: GIS Applications
Produced by: Terri McRitchie
Date created: 2019 March 27

Other beneficial
research would be
to study mitigation
efforts such as soil
bioengineering
techniques to
protect sensitive
sites from
geological hazards.

Citations
Environmental Systems Research Institute, Inc. 2018. Using raster
data for site selection: using fuzzy logic for site selection. United
States of America: Esri. [accessed 2019 Feb 18]. Online training.
Data obtained by: Tom Bradley, GIS Analyst