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Open-File Report O-23-03, Multi-Hazard Risk Report for the City of Cottage Grove, Oregon, by Matt C. Williams and Nancy C. Calhoun; 57 p. report, 8 tabloid size map plates, one Esri® geodatabase with internal metadata, external metadata in .xml format.

What's in this report?
This report describes the methods and results of multi-hazard risk assessment for the City of Cottage Grove, Oregon. The risk assessment can help a community better plan for disaster.

Report downloads:

Text report, including all appendices (57 p., 9.0 MB PDF)
Appendix E. Map Plates (8 plates; 80.8 MB zip file; view/download individual plates below)
GIS metadata bundle(3 .xml files; 20 KB zip file)
Full GIS data bundle, with .xml metadata (3.1 MB, zip file; view .xml metadata links below)
Complete publication bundle (92.0 MB zip file)

EXECUTIVE SUMMARY

This report was prepared for the City of Cottage Grove, Oregon, with funding provided by the Oregon Department of Land Conservation and Development (DLCD). It describes the methods and results of the natural hazard risk assessment performed in 2022 by the Oregon Department of Geology and Mineral Industries (DOGAMI). The purpose of this project is to provide the City of Cottage Grove with a detailed risk assessment information to enable them to compare hazards and act to reduce their risk. The risk assessment results quantify the impact of natural hazards to this community and enhance the decision-making process in planning for disaster.

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

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. Each hazard dataset was the best available at the time of writing.
In the third task, we analyzed risk 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 and wildfire.

We performed this assessment using the best data available at the time of the study. However, it is important to note that some of the datasets used in this study will likely be updated and replaced within the next three years. The landslide hazard maps as well as the geohazard maps that inform the earthquake model are several decades old and not based on lidar topography. The flood dataset used was the draft FEMA flood depth maps produced in 2022. Changes to any of the datasets in the coming years will need to be incorporated into future, more accurate risk assessments.

The findings and conclusions of this report show the potential impacts of hazards in the City of Cottage Grove. An earthquake can cause widespread damage and losses throughout the community. Hazus-MH earthquake simulations illustrate the potential reduction in earthquake damage through seismic retrofits. Our findings also indicate that many of the critical facilities in the study area that were built before seismic building code standards are at high risk from earthquake hazard. Areas along much of the Coast Fork Willamette River are at risk from flooding. Our analysis shows that new landslide mapping based on improved methods and lidar information will increase the accuracy of mapping. Wildfire risk is low for the study area, but moderate and high wildfire hazard areas are present to the east and south. We also found that the 100-year flood poses the greatest potential of population displacement compared to other hazard scenarios analyzed in this study.

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.

Selected Cottage Grove Results Total buildings: 5,776 Total estimated building value: $1.56 billion
Cascadia Subduction Zone (CSZ) Magnitude (Mw) 9.0 Earthquake Red-tagged buildings^a: 28 Yellow-tagged buildings^b: 290 Loss estimate: $112 million	100-year Flood (2022 FEMA draft data) Number of buildings damaged: 451 Loss estimate: $6.9 million
Landslide (High and Very High- Susceptibility) Number of buildings exposed: 44 Exposed building value: $12 million	Wildfire (High Risk) Number of buildings exposed: 0 Exposed building value: $0
^aRed-tagged buildings are considered uninhabitable due to complete damage. ^bYellow-tagged buildings are considered limited habitability due to extensive damage.

GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.7 format.
Metadata is embedded in the geodatabases and is also provided as separate .xml format 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.