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Open-File Report O-23-01, Multi-Hazard Risk Report for Tillamook County, Oregon, including the cities of Bay City, Garibaldi, Manzanita, Nehalem, Rockaway Beach, Tillamook, and Wheeler and the unincorporated communities of Bayside Gardens, Neskowin, Oceanside, Netarts, and Pacific City, by Matt C. Williams and Nancy C. Calhoun; 111 p. report, 11 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 a natural hazard risk assessment for Tillamook County communities. The risk assessment can help communities better plan for disaster.

Report downloads:

Text report, including all appendices (111 p., 14.3 MB PDF)
Appendix E. Map Plates (11 plates; 79.5 MB zip file; view/download individual plates below)
GIS metadata bundle(3 .xml files; 19 KB zip file)
Full GIS data bundle, with .xml metadata (5.0 MB, zip file; view .xml metadata links below)
Complete publication bundle (96 MB zip file)

EXECUTIVE SUMMARY

This report was prepared for the communities of Tillamook County, 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) 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 assessment results quantify the impact of natural hazards to each 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. Using 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 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, coastal erosion, and wildfire.

The findings and conclusions of this report show the potential impacts of hazards to communities within Tillamook County. A Cascadia Subduction Zone (CSZ) event (earthquake and tsunami) will cause extensive damage and losses throughout the county. Our findings indicate that most of the study area’s critical facilities are at high risk during a CSZ event. We demonstrate the potential for the reduction in damages and losses from seismic retrofits through building code simulations in the Hazus-MH earthquake model. We also found that the hazards with the highest potential of population displacement are earthquake, tsunami, and landslide hazards. Flooding is a threat for some communities in the study area and we quantify the number of elevated structures that are less vulnerable to flood hazard. Our analysis shows that areas with moderate to steep slopes or at the base of steep hillsides are at greatest risk to landslide hazards, which are present throughout the communities and rural county. Over 1,200 buildings along the coast of Tillamook County were exposed to coastal erosion. Wildfire exposure analysis show a higher risk for buildings within the wildland-urban interface (WUI) portions of the county.

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. This analysis improves on the 2020 DOGAMI natural hazard risk assessment, which relied on less accurate and outdated hazard and building data.

Results were broken out for the following geographic areas:

Unincorporated Tillamook County (rural)
Community of Bayside Gardens
Community of Neskowin
Communities of Oceanside and Netarts
Community of Pacific City
City of Bay City
City of Garibaldi
City of Manzanita
City of Nehalem
City of Rockaway Beach
City of Tillamook
City of Wheeler

Selected Countywide Results Total buildings: 27,090 Total estimated building value: $6.9 billion
Cascadia Subduction Zone Magnitude-9.0 Earthquake^a Red-tagged buildings^b: 2,123 Yellow-tagged buildings^c: 5,541 Loss estimate: $1.5 billion	Cascadia Subduction Zone Magnitude-9.0 Tsunami Inundation Number of buildings damaged: 4,931 Loss estimate: $1 billion
Happy Camp Fault Magnitude-6.6 Earthquake Scenario Red-tagged buildings^b: 1,136 Yellow-tagged buildings^c: 3,648 Loss estimate: $992 million	100-year Flood Scenario Number of buildings exposed: 2,574 Loss estimate: $91 million
Landslide Exposure (High and Very High Susceptibility) Number of buildings exposed: 9,690 Exposed building value: $2 billion	Coastal Erosion Exposure (Moderate Hazard) Number of buildings exposed: 1,227 Exposed building value: $280 million
Wildfire (High and Moderate Risk) Number of buildings exposed: 657 Exposed building value: $136 million
^aResults reflect damage caused by the earthquake to buildings outside of the tsunami zone. The combined earthquake and tsunami results estimate the total damage from a CSZ Mw-9.0 event. ^bRed-tagged buildings are considered to be uninhabitable due to complete damage. ^cYellow-tagged buildings are considered to be of 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.