There have been five major floods on the lower Columbia since 1894, including the 1948 Vanport Flood, which displaced over 18,000 residents and killed at least 15 people. Despite this history, and the immense growth in the area, there’s been a limited understanding of the flood risk posed if a portion of the levee were to fail today. That is no longer true thanks to a study conducted by the Oregon Department of Geology and Mineral Industries (DOGAMI). DOGAMI’s newly published study, “Flood Risk Assessment for the Columbia Corridor Drainage Districts in Multnomah County, Oregon,” quantifies the impacts of levee failure during a 100- or 500-year flood (floods that have a 1% or .2% chance of occurring annually).
The DOGAMI study looked at the impacts of flooding in the five independent drainage districts responsible for operating and maintaining the levees along the Columbia River in urban Multnomah County: 1. Sauvie Island Drainage & Improvement Company (SIDIC), 2. Peninsula Drainage District #1 (PEN 1), 3. Peninsula Drainage District #2 (PEN 2), 4. Multnomah County Drainage District (MCDD), and 5. Sandy Drainage & Improvement Company. Four our purposes, we’ve focused on the four mainland districts in Portland, Gresham, Fairview, and Troutdale (PEN 1, PEN 2, MCDD, and SDIC) that manage portions of the 27-mile Columbia Corridor levee system.
75% of the approximately 7,500 residents who live in Columbia Corridor are at risk of flooding associated with levee failure during a high water event. The majority of the residents in the corridor live in MCDD or PEN 2, including approximately 1,400 inmates at two prisons located in MCDD. In PEN 2, more than 2,200 of the 2,500 residents would be displaced due to levee failure in that area during a major flood. 3,260 of MCDD’s roughly 5,000 residents would initially experience displacement.
Although the study focused on the residents that could be displaced due to flooding associated with levee failure during a major flood, we would note that the following neighborhoods are vulnerable:
- East Columbia
- sections of Cully and Sumner on the north side of Columbia Blvd.
- sections of Parkrose, Argay, Wilkes, and North Gresham to the north of Sandy Blvd.
- the part of Fairview to the north of Sandy Blvd, including Fairview Lake
- North of Highway 30 in Troutdale
* at an elevation of about 39 feet, Interlachen is not technically in a flood zone, however, it is completely surrounded by lower land that is vulnerable to flooding. If the levee failed on the eastern side of MCDD, the roads accessing Interlachen would likely become completely impassable.
Most businesses in the districts would be forced to close after a major flood and it could take months or even years for some of those businesses to reopen.
Employees & Wage Loss
The jobs located in the historic floodplain account for about 10% of all of the jobs in Multnomah County. A large proportion of manufacturing and industrial jobs in the county are located in the area. Business closures in the Columbia Corridor would result in substantial loss in wages throughout the region.
The assessment also identified important infrastructure that is at risk of flooding like the Columbia South Shore Well Field, Oregon’s 2nd largest source of drinking water, and transportation systems, including sections of I-5, I-84, and I-205, that could become impassable depending on the location of a levee breach.
Over 140 miles of road, rail, and transit lines are located in the corridor, including bus lines, light rail, and emergency routes that we rely on as a community. The potential transportation impacts in MCDD make up the greatest proportion of transportation lines and routes within the districts and MCDD has the largest overall exposure ratio with approximately half of the transportation lines impacted or impassable during a 100-year flood.
Here are some of the possible impacts identified:
- Marine Drive is vulnerable to flooding throughout the districts, particularly in PEN 1 and PEN 2.
- Airport Way, NE 33rd, NE 82nd, NE 112nd and NE 223rd are all vulnerable to flooding in MCDD which will create challenges for companies in the corridor and throughout the state that need to access the Port of Portland facilities to move goods to market.
• Martin Luther King Jr. Boulevard, I-205, Columbia Boulevard, and Sandy Boulevard should remain widely passable as long as the railroad embankment on the western end of PEN 1 remains intact.
• A section of I-84 in SDIC and I-5 in PEN 1 would be impassable during a 500-year flood.
- All ten of the large parking lots in MCDD, including those at the Portland International Airport, will experience 4-7 feet of flooding during a 100- or 500-year flood. That level of flooding would result in complete destruction of cars, trucks, and SUVs.
- Bus lines along Marine Drive, Martin Luther King Jr. Boulevard, Vancouver Way, Airport Way, NE 105th Avenue, NE 33rd Avenue and Frontage Road could be disrupted due to flooding along with portions of the Yellow and Red MAX light rail lines.
- Many of the designated emergency routes in each of the districts will be impassable.
There are many different types of hazardous materials stored in buildings throughout the districts that could become exposed to floodwaters. This would further exacerbate a crisis situation, causing additional health hazards and ecological damage.
Community Assets & Resources
A number of natural spaces, recreational amenities, and places the community values are also vulnerable to flooding. This includes critical transportation hubs like the Portland International Airport, local nonprofits like the Oregon Humane Society and Oregon Food Bank, parks and recreational areas like Blue Lake Regional Park and the Columbia Children’s Arboretum, and shopping centers like Cascade Station, home to the state’s only IKEA.