DOGAMI OPEN-FILE REPORT SERIES

[Go back] | Publications Center | DOGAMI Home

PUBLICATION PREVIEW

 Open-File Report O-22-05, Multi-Hazard Risk Report for Marion County, Oregon, including the cities of Aumsville, Aurora, Detroit, Donald, Gates, Gervais, Hubbard, Idanha, Jefferson, Keizer, Mill City, Mt. Angel, Salem, Scotts Mills, Silverton, St. Paul, Stayton, Sublimity, Turner, and Woodburn and the unincorporated communities of Brooks, Butteville, Four Corners, Hayesville, Labish Village, Marion, Mehama, and West Salem, by Matt C. Williams and Ian P. Madin; 136 p. report, 8 tabloid size map plates, one Esri® geodatabases with internal metadata, external metadata in .xml format.

What's in this report?
This report describes the methods and results of natural hazard risk assessments for Marion County communities. The risk assessments can help communities better plan for disaster.

Report downloads:

EXECUTIVE SUMMARY

This report was prepared for the communities of Marion County, Oregon, with funding provided by the Federal Emergency Management Agency (FEMA). It describes the methods and results of the natural hazard risk assessments performed in 2021 and 2022 by the Oregon Department of Geology and Mineral Industries (DOGAMI) within the study area. The purpose of this project is to provide communities with detailed risk assessment information to enable them to compare hazards and act to reduce their risk. The risk assessments contained in this project quantify the impacts of natural hazards to these communities and enhances the decision-making process in planning for disasters.

We arrived at our findings and conclusions by completing three main tasks for each community: compiling an asset database, identifying and using the best available hazard data, and performing natural hazard risk assessments.

In the first task, we created a comprehensive asset database for the entire study area by synthesizing assessor data, U.S. Census information, FEMA Hazus®-MH general building stock information, and building footprint data. This work resulted in a single dataset of building points and their associated building characteristics. With these data we were able to represent accurate spatial locations and vulnerabilities on a building-by-building basis.

The second task was to identify and use the most current and appropriate hazard datasets for the study area. Most of the hazard datasets used in this report were created by DOGAMI and were produced using high-resolution, lidar topographic data. Although not all the data sources used in the report provide complete, countywide information, each hazard dataset used was the best available at the time of the analysis.

In the third task, we performed risk assessments using Esri® ArcGIS Desktop® software. We took two risk assessment approaches: (1) estimated loss (in dollars) to buildings from flood (recurrence intervals) and earthquake scenarios using the Hazus-MH methodology, and (2) calculated the number of buildings, their value, and associated populations exposed to earthquake, and flood scenarios, or susceptible to varying levels of hazard from landslides, channel migration, wildfire, and volcanic lahar.

The findings and conclusions of this report show the potential impacts of hazards in communities within Marion County. Earthquakes: Although earthquake damage will occur throughout the entire county, extensive damage and losses are more probable in the northeastern portion of the county near the Mt. Angel Fault and areas with liquefaction-prone soils. Our findings indicate that most of the critical facilities in the study area are at High risk from an earthquake. We used multiple Hazus-MH earthquake simulations to illustrate the potential reduction in earthquake damage through seismic retrofits. Flooding: Some communities in the study area have moderate risk from flooding and we found only a small percentage (<1%) of flood exposed buildings were elevated above the 100-year flood elevation. Landslides: Our analysis shows that areas with moderate to steep slopes or at the base of steep hillsides are at greatest risk from landslide hazards, such as along the North Santiam River, the communities of Mt. Angel and Scotts Mills, and southwestern portions of Salem. Channel migration zone hazards: Nearly 826 buildings along the Pudding River and Santiam and North Santiam Rivers were exposed to channel migration hazard. Wildfires: The wildfire hazard data used in this study were created prior to the unprecedented 2020 Labor Day Wildfires, however the results corresponded to the actual impacts of the 2020 Labor Day Wildfires in the county. Volcanic-lahar hazards: Lahar hazard is a potential risk and could have significant impact for areas and the communities along the North Santiam River.

The information presented in this report is designed to increase awareness of natural hazard risk, to support public outreach efforts, and to aid local decision-makers in developing comprehensive plans and natural hazard mitigation plans. This study can help emergency managers identify vulnerable critical facilities and develop contingencies in their response plans. The results of this study are designed to be used to help communities identify and prioritize mitigation actions that will improve community resilience.

Results were broken out for the following geographic areas:

* Portions of the cities of Detroit, Gates, and Mill City that were within Linn County are included in this report. The City of Salem that was within Polk County was examined individually and designated as City of Salem (West Salem).


Selected Countywide Results
Total buildings: 170,562
Total estimated building value: $62 billion

Mt. Angel Deterministic 
Magnitude 6.8  Earthquake Scenario  

Red-tagged buildingsa: 7,479
Yellow-tagged buildingsb: 17,028
Loss estimate: $6.7 billion

100-year Flood Scenario
Number of buildings damaged: 2,552
Loss estimate: $126 million

Landslide Exposure (High and Very High-Susceptibility)
Number of buildings exposed: 7,470
Exposed building value: $2.7 billion

Channel Migration Zone (Erosion Hazard Area - 30-year) 
Number of buildings exposed: 826
Exposed building value: $300 million

Wildfire Exposure (High and Moderate Risk)
Number of buildings exposed: 2,819
Exposed building value: $814 million

Lahar Exposure (1,000 to 15,000-year) 
Number of buildings exposed: 1,789
Exposed building value: $415 million

aRed-tagged buildings are considered to be uninhabitable due to complete damage.
bYellow-tagged buildings are considered to be of limited habitability due to extensive damage.  

 


GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA

Geodatabases are Esri® version 10.7 format.
Metadata is embedded in the geodatabases and is also provided as separate .xml formatted files.

Each dataset listed below has an associated, standalone .xml file containing metadata in the Federal Geographic Data Committee Content Standard for Digital Geospatial Metadata format.

Marion_County_Risk_Report_Data.gdb:

Feature dataset: Asset_Data

 

 

Building_footprints

polygons

.xml

Communities

polygons

.xml

UDF_points

points

.xml


APPENDIX E: MAP PLATES (PDFs, 17 x 11 inches each)

Plate 1, Building Distribution Map of Marion County, Oregon (12.6 MB PDF)

MapDescription automatically generated

 

 

Plate 2, Population Density Map of Marion County, Oregon (10.7 MB PDF)

 

 

Plate 3, Mt. Angel Fault Magnitude-6.8 Earthquake Shaking Map of Marion County, Oregon (5.2 MB PDF)

 

 

Plate 4, Flood Hazard Map of Marion County, Oregon    (11.8 MB PDF)

 

 

Plate 5, Landslide Susceptibility Map of Marion County, Oregon (12.3 MB PDF)

 

 

Plate 6, Channel Migration Zone Map of Marion County, Oregon (11.1 MB PDF)



Plate 7, Wildfire Risk Map of Marion  County, Oregon  (11.1 MB PDF)

 



Plate 8, Lahar Exposure Map of Marion County, Oregon  (10.6 MB PDF)