Natural Hazards Mitigation Planning

Multnomah County is working on an update to the Multi-Jurisdictional Natural Hazards Mitigation Plan.

Updated October 20, 2023

THE 2023 NATURAL HAZARDS MITIGATION PLAN UPDATE WAS ADOPTED BY THE MULTNOMAH COUNTY BOARD OF COMMISSIONERS.

The update to the Multnomah County Multi-Jurisdictional Natural Hazards Mitigation Plan (NHMP) was adopted by resolution of the Multnomah County Board on October 13. The final version of the plan is posted below, and incorporates comment from the Oregon Department of Emergency Management (OEM) and Federal Emergency Management Agency (FEMA). The plan received final federal review approval on August 24, 2023, and may be now be adopted by all of the participating jurisdictions and districts. A list of adoption dates by each multi-jurisdictional partner will be added to this page soon. This plan update was built through stakeholder input, public comment, and the most up-to-date studies and research about natural hazard risk in Multnomah County.

Landslide and erosion at Rock Creek Road in western Multnomah County
Landslide and erosion at Rock Creek Road in western Multnomah County. Photo from Multnomah County Roads Department.
The plan provides a comprehensive view of the risks to Multnomah County from earthquake, flood, landslide, severe weather, volcano, and wildfire and wildfire smoke – and strategies for lessening the impact of those future disasters. The plan update has been in process since 2021 and includes the Cities of Fairview, Gresham, Troutdale and Wood Village; Multnomah County; the Columbia Corridor Drainage Districts (Peninsula 1, Peninsula 2, Multnomah County Drainage District, and Sandy Drainage Improvement Company plus two future consolidated districts); and the Port of Portland. The City of Portland has their own Mitigation Action Plan, which was recently updated.

Continuing comments may be submitted through this survey form, with responses to be maintained for future edits or versions of the plan. The plan update and comment form are only available in English. Information about this update and natural hazards in Multnomah County are available in: 中文(Chinese)| Русский (Russian)| Soomaali (Somali)| Español (Spanish)| Tiếng Việt (Vietnamese)

DRAFT PLAN UPDATE CONTENTS

What is the Natural Hazards Mitigation Plan and why is it being updated?

Every five years, Multnomah County is required by the Federal Emergency Management Agency (FEMA) to update its Natural Hazards Mitigation Plan (NHMP). This plan uses the best available information about natural hazards to come up with actions to protect life, property and the environment in future natural disasters. The current plan was completed in 2017, and will be updated in 2023 by local adoption, after approval from FEMA and the Oregon Department of Emergency Management (OEM).

What is Hazard Mitigation?

Hazard mitigation is the work that is done before a disaster occurs, to lessen the severity of future natural disasters and make the community more resilient.

Successful hazard mitigation projects protect lives and property and also save the community money in the long run. It is estimated by FEMA that for every dollar spent on hazard mitigation, up to six dollars are saved when disasters strike.

What Hazards Are Covered in This Plan?

This plan only covers natural hazards; human-caused disasters such as terrorism and hazardous materials are covered in other plans. The State of Oregon lists natural hazards that have impacts across Oregon. Multnomah County communities plan for all of those except for coastal erosion and tsunami, which generally only damage coastal communities.

Multnomah County's hazard mitigation plan addresses the hazards listed below. The majority of these hazards are being impacted by climate change, and so it is more important than ever to prepare, because current information may underestimate the amount of risk we face.

Types of earthquakes in the Pacific Northwest
United States Geological Survey
EARTHQUAKES are rare in Oregon, but are a big threat. The last subduction zone earthquake to impact Oregon occurred in 1700 and quakes of this type are estimated to happen every 300-600 years or so. Multnomah County also has crustal faults (like the San Andreas Fault). There faults are less likely to happen than a subduction zone earthquake, but could be even more damaging in some parts of the county. Typical mitigation actions for earthquakes include:
  • Increasing public awareness of risk and how to respond in an earthquake.
  • Assisting residents gathering supplies in their homes to use after a severe earthquake.
  • Supporting strengthening of bridges, levees, stone buildings, and other structures.

Damage from 1964 Christmas Flood
1964 Christmas Flood (Photo: Levee Ready Columbia)
FLOODS happen every year in Oregon, at least on local roads and neighborhoods. While widespread flooding is less frequent, large floods have impacted Multnomah County in 1956, 1964 and 1996, and a breach of a railroad embankment destroyed the Vanport community in 1948. Typical mitigation actions for flood include:
  • Strengthening levees, dams, and floodwalls.
  • Preserving floodplains as open space.
  • Encouraging flood insurance to increase resilience of homes and businesses.

Historic Bonneville Landslide Map
Bonneville Dam was the site of a massive landslide about 500 years ago (Graphic: Dan Coe, Washington Department of Natural Resources)
LANDSLIDES also happen frequently, but are usually small. Larger landslides may be most likely to happen at the same time as floods or earthquakes. Steep slopes that have burned in wildfires are also at high risk, as occurred in a tragic 2020 landslide in Dodson, in eastern Multnomah County. Typical mitigation actions for landslide include:
  • Stabilizing slopes with trees and other vegetation.
  • Limiting new construction in the highest hazard areas.

SEVERE WEATHER includes extreme heat, winter storms, wind storms, and drought. Unfortunately, all of these hazards are becoming more extreme and unpredictable due to climate change.

2017 Multnomah County Winter Storm Photo
2017 Multnomah County Winter Storm (Photo: Multnomah County)
The June 2021 heatwave has shown how dangerous these weather events can be, as well as the 2017 winter that also claimed multiple lives in Multnomah County. Typical mitigation actions for severe weather include:
  • Reducing urban heat effects by planting more trees.
  • Advertising summer and winter shelter planning for those without climate-controlled living spaces.
  • Promoting the use of anchors and tie-downs to protect manufactured homes in high winds.

Mount Hood Volcanic Hazards
United States Geological Survey (USGS)
VOLCANOS are very rare events, but could carry high risk. Mount Hood is a nearby active volcano that could severely impact Multnomah County and is believed to have last had a major eruption around 1731. Mount Saint Helens erupted in 1980, but ash blew east, sparing Multnomah County from the worst air quality effects. Typical mitigation actions for volcano include:
  • Publicizing community evacuation routes.
  • Developing improved early warning systems.

Wildfire Smoke in Multnomah County 2020
2020 Multnomah County Wildfire Smoke (Photo: Another Believer, Wikimedia Commons)
WILDFIRES AND WILDFIRE SMOKE are a risk every summer, especially considering the health risks from smoke, which may come from fires in other parts of the state or even outside Oregon. Summers have been becoming hotter and drier, raising concerns almost everywhere in Multnomah County. The 2017 Eagle Creek Fire burned almost 50,000 acres in Multnomah and Hood River Counties, destroyed four buildings, and closed down recreational areas in the Gorge for years. Typical mitigation actions for wildfires include:
  • Assisting homeowners to create defensible space around homes and other structures.
  • Removing invasive species to make forests more fire resistant.
  • Upgrading air filtration in spaces that can be used as clean-air shelters.

To learn more about these hazards, go to Community Resources for Hazard Mitigation (English only). You can see maps of hazards at the following websites:

  • HazVu - Oregon Department of Geology and Mineral Industries (DOGAMI) site shows earthquake, landslide, and volcano risk by address throughout Oregon. (In English)
  • Oregon Wildfire Explorer - Oregon Department of Forestry (ODF) site shows wildfire risk by address throughout Oregon. (In English)
  • National Flood Hazard Layer (NFHL) - Federal Emergency Management Agency (FEMA) website shows mapped flood risk by address across the United States. (In English)
  • Metro Regional Barometer - Climate and Environment - Series of Metro Regional Government maps including Urban Heat Islands - locations where heat risk is the most severe. (In English)

Questions?

Contact David Lentzner, Planning Division - david.lentzner@multco.us or by phone at 503.679.3275.

Last reviewed December 2, 2024

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