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IMS-60, Landslide hazard and risk study of Eugene-Springfield and Lane County, Oregon, by Nancy C. Calhoun, William J. Burns, Jon J. Franczyk, and Gustavo Monteverde

OVERVIEW: The study identifies areas in Eugene-Springfield and the surrounding area where landslides are more likely to happen – and how many people and buildings are at risk when they do. The study, which included the cities of Eugene, Springfield, and Coburg, the unincorporated communities of Goshen and Walterville, and areas of unincorporated Lane County, shows areas where taking action to reduce landslide risk could make a big difference.

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IMS-60 REPORT SUMMARY
This Eugene-Springfield landslide hazard and risk study was undertaken by the Oregon Department of Geology and Mineral Industries (DOGAMI) in order to create detailed, usable maps and analyses on the level and location of the landslide hazard and risk to infrastructure in the study area. This project was funded by the Federal Emergency Management Agency Risk MAP (Mapping, Assessment, and Planning) Program (EMW-2015-CA-00106). Lane County has experienced hundreds of landslides in the past 50 years. Many of these have been recorded in the Statewide Landslide Information Database for Oregon (SLIDO); however, no landslide hazard study has been conducted in the most populous portion of the county: the Eugene-Springfield metro area. The cities of Springfield and Eugene are growing at a rate of 5% to 7.7% annually (U.S. Census 2010) and, as this is the second most populated metro area in Oregon, understanding landslide hazards and risk from landslides is important for citizens and those addressing natural hazards in their organizations.

For this study we used the protocols established by DOGAMI for 1) making a landslide inventory; that is, mapping existing landslide deposits, 2) modeling deep and shallow landslide susceptibility in order to demonstrate where landslides may occur in the future, and 3) assessing landslide risk through exposure analysis and by using the FEMA Hazus-MH model. These established methods allow for a consistent scientific framework and comparison to other areas in Oregon to understand relative risk.

The study area is 230 mi2 (595 km2 ) centered on the Eugene-Springfield and Coburg urban growth boundaries with a buffer to include as much of the surrounding populated areas of Lane County as our project scope and available lidar coverage allowed. Our results include the following:

To better understand the results, we divided the study area into subsections, defined by communities. The landslide hazard is concentrated in a few communities. Notably, in the hills south of Eugene, southeast of Springfield, and throughout unincorporated Lane County, there is markedly more landslide hazard than in the dominantly flat, alluvial terrain in north-central and western Eugene, and in western Springfield along the McKenzie River and Willamette River.

The results led us to conclude that, overall, the study area experiences moderate landslide hazard and risk, with both concentrated in a few communities in the study area. We recommend:

The primary landslide hazard in the study area is exposure of existing structures to deep landslides. Substantive risk reduction activities for this type of landslide hazard include controlling the input of water onto slopes within the moderate and deep landslide susceptibility zones and on existing deep landslides, and avoiding adding material (weight) to the tops of susceptible slopes or, conversely, removing material from the bottoms of slopes (excavation or grading).



GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.1 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.

The GIS data included with this publication are in an ArcGIS version 10.1 file geodatabase.

Eugene_Springfield_landslide_GIS_IMS_60.gdb (GIS data bundle, 43.2 MB zip file)
Building feature dataset:   Metadata bundle (zip)
      building_footprints Polygons. This feature class GIS dataset contains building footprints depicting building shape and location in the Eugene-Springfield metro area. The building footprint were digitized from high resolution lidar and orthoimagery.</ .xml
Engineering_Geology feature dataset:    
      Eugene_Bedrock_Geo Polygons. This layer is a bedrock engineering geology map, for use in the deep landslide susceptibility model (per methods explained in DOGAMI's Special Paper 48). This map is an interpretation from geologic mapping derived the compilation Oregon Geologic Data Compilation 6 (OGDC 6), based dominantly on the geologic mapping from McClaughry and others, 2010 .xml
      Eugene_Surficial_Geo Polygons. This layer is a surficial engineering geology map, for use in the shallow landslide susceptibility model (per methods explained in DOGAMI Special Paper 45). This map is an interpretation from geologic mapping derived the compilation Oregon Geologic Data Compilation 6 (OGDC-6), based dominantly on the geologic mapping from McClaughry and others, 2010. We also used the soil survey for Lane County, in order to best understand what materials are present in the top 15 feet of material at the surface (USDA, 1987). .xml
Landslide_Inventory feature dataset:    
      Historic_landslide_points.xml

Points. Historic Landslide Points is a compilation of center points of published or known historic (roughly 1979-2016) landslides and any available information about these landslides including damage and losses and several other attributes within Eugene-Springfield and central Lane County.

.xml
      Deposits.xml Polygons. Historic Landslide Points, is a compilation of center points of published or known historic (roughly 1979-2016) landslides and any available information about these landslides including damage and losses and several other attributes within Eugene-Springfield and central Lane County.</ .xml
      Scarps_Flanks.xml Lines. Scarp flank polygons are used to estimate of future retrogressive failure distance behind the head scarp, aid in type classification, and assigning a confidence value for the landslide.</ .xml
      Scarps.xml Polygons. This feature class represents lines of the uppermost extent of landslide head scarp and any internal scarps in the body of the landslide. .xml
      Eugene_Shallow_Susc.xml Raster. This layer is a shallow landslide susceptibility raster dataset. The symbology on this map includes low, moderate, and high susceptibility. The main components used to create the zones include 1) using a landslide inventory, 2) calculating regional slope stability factor of safety (FOS), 3) removing isolated small elevation changes (to reduce over-prediction), 4) creating buffers to add susceptible areas missed in a grid-type analysis (to reduce under-prediction), and 5) combining the four components into final susceptibility hazard zones. .xml
      Eugene_Deep_Susc.xml
Polygons. This layer is a deep landslide susceptibility map. The symbology on this map includes high and moderate susceptibility. The deep susceptibility zones were established based upon location and proximity feature class consists of polygons delineating landslide deposits (including debris flow fans and talus extent) within central Lane County, Oregon. .xml

PLATES (PDFs, 60 by 38 inches each; scale 1:34,000)

Plate 1. Landslide inventory map of Eugene and Springfield, Lane County, Oregon
high-resolution | low-resolution


Plate 2. Shallow landslide susceptibility map of Eugene and Springfield, Lane County, Oregon
high-resolution | low-resolution


Plate 3. Deep landslide susceptibility map of Eugene and Springfield, Lane County, Oregon
high-resolution | low-resolution