Flood Risk Assessment

Two maps - one circa 1917 showing the area right after the drainage districts were created, with the area as a natural floodplain, the second showing the area today, which is heavily developed

The area along the Columbia River in Multnomah County was once a natural floodplain that flooded seasonally. Today, it's a major transportation hub for our state. It's a critical economic engine with important historical, cultural, and environmental value and a destination for business, recreation, and entertainment.

In 1948, a section of the 27-mile levee system that runs along the Columbia failed and the entire city of Vanport was destroyed in just a few hours. What would happen if a section of our levee system failed today?

The Oregon Department of Geology and Mineral Industries (DOGAMI) helped us answer this question by modeling potential impacts from a levee breach during a major flood on the Columbia River. See below for highlights and a link to the full study.

a banner that says Columbia Corridor Risk Assessment Highlights

Residents Displaced

About 7,500 residents live along the Columbia River and Columbia Slough. Approximately 75% are at risk of being displaced due to flooding associated with levee failure during a major flood on the Columbia.

a pie chart showing 75% of residents living behind the levees are at risk of being displaced by levee failure during a major flood

a pie chart showing 63-73% of businesses are at risk of being closed for over one year after levee failure during a major flood

Businesses Disrupted

A majority of the businesses along the Columbia River and Columbia Slough are at risk of flooding. Depending on the location of the levee failure, up to 75% of the local businesses could be forced to close, and it could take up to two years or longer for some businesses to fully recover.

Employees Impacted & Wages Lost

Over 59,000 employees work in the managed floodplain behind the Columbia River levee system in Multnomah County. Any disruption in business operation in the area would result in the loss of jobs and wages, which would create challenges for workers and their families throughout the region.

A graph shows that 58,864 jobs are at risk of flooding if the levee system failed.

A graph showing that 2.8 billion dollars wages could be lost due to flooding of the levee system.

Important Infrastructure

Critical public infrastructure is located along the Columbia River, including:

3 water treatment facilities, including Oregon’s 2nd largest source of drinking water
3 interstate highways
8 electrical substations
2 natural gas facilities
Several TriMet MAX and bus lines

a map of areas where transportation will be affected by flooding

HAZARDOUS MATERIALS

There are a number of hazardous materials stored in buildings along the Columbia River and Columbia Slough that could become exposed to floodwaters during a levee breach and flood. This includes common household items like paint, paint thinners, and certain types of fertilizers. The exposure of these materials would make an emergency situation much worse by causing serious health hazards, as well as ecological damage in the immediate area and downstream.