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 Open-File Report O-21-06, Natural hazard risk report for Sherman County, Oregon, including the Cities of Grass Valley, Moro, Rufus, and Wasco,
by Matt C. Williams and Ian P. Madin; 62 p. report, 6 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 Sherman County communities. The risk assessment can help communities better plan for disaster.

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EXECUTIVE SUMMARY

This report was prepared for the communities of Sherman County, Oregon, with funding provided by the Federal Emergency Management Agency (FEMA). It describes the methods and results of the natural hazard risk assessment performed in 2018 and 2021 by the Oregon Department of Geology and Mineral Industries (DOGAMI) within the study area. The purpose of this project was to provide communities with a detailed understanding of their risk from natural hazards, to give communities the ability to compare their risk across multiple hazards, and to prioritize and take actions that will reduce risk. The results of this study can also inform the natural hazard mitigation planning process.

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

To complete the first task, we created a comprehensive asset database for the entire study area by synthesizing assessor data, U.S. Census information, 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 this dataset, we were able to represent accurate spatial location and vulnerability 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 some were produced using high-resolution lidar topographic data. While not all the data sources used in the report are countywide, each hazard dataset was the best available at the time the analysis was performed.

In the third task, we performed the risk assessment using Esri® ArcGIS Desktop® software. We used two risk assessment approaches: (1) estimated loss (in dollars) to buildings from flood (recurrence intervals) and earthquake scenarios using FEMA Hazus®-MH methodology, and (2) calculated number of buildings, their value, and associated populations exposed to earthquake, flood, landslide, and wildfire hazards.

The findings and conclusions of this report show the potential impacts of hazards in communities within Sherman County. An earthquake can cause minor to moderate damage and losses throughout the county.  The communities of Grass Valley and Moro have moderate risk from flooding, and we quantify the number of elevated structures that are less vulnerable to flood hazard in the study area. Our analysis shows that new landslide mapping based on improved methods and lidar information will increase the accuracy of future risk assessments. During the time of writing, the best available data show that wildfire risk is high for the overall study area. Our findings indicate that most of the critical facilities in the study area are at high risk from an earthquake and wildfire. We also note that the biggest causes of population displacement are wildfire and flood hazards. Lastly, we demonstrate that this risk assessment can be a valuable tool to local decisionmakers.

Results were broken out for the following geographic areas:

 

 

 

 

 

 

 

 

 

Selected Study Area Results
Total buildings: 2,405
Total estimated building value: $543 million

2,500-year Probabilistic Magnitude 7.0 Earthquake
Red-tagged buildingsa: 13
Yellow-tagged buildingsb: 58
Loss estimate: $37 million

100-year Flood Scenario
Number of buildings damaged: 68
Loss estimate: $1.9 million

Landslide Exposure (High and Very High Susceptibility)
Number of buildings exposed: 29
Exposed building value: $7.7 million

Wildfire Exposure (High Risk)
Number of buildings exposed: 273
Exposed building value: $53 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

Geodatabase is Esri® version 10.2 format.
Metadata is embedded in the geodatabase 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.

Sherman_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 Sherman County, Oregon (4.6 MB PDF)

 

 

 

 

Plate 2, Population Density Map of Sherman County, Oregon (5 MB PDF)

 

 

 

 

 

Plate 3, CSZ Mw 9.0 Earthquake Shaking Map of Sherman County, Oregon (6 MB PDF)

 

 

 

 

 

Plate 4, Flood Hazard Map of Sherman County, Oregon  (5.6 MB PDF)

 

 

 

 

 

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

 

 

 

 

 

Plate 6, Wildfire Hazard Map of Sherman County, Oregon (5 MB PDF)