City  Government

Understanding Portland’s Big Pipes

The vital infrastructure project has drastically reduced the amount and frequency of sewer overflow events in the Willamette River and Columbia Slough.

February 8, 2023 • 
Ben McBee
A vehicle drives toward the viewer in a massive sewer pipe

CSOs are now fewer, smaller in volume, and shorter in duration.

Photo via City of Portland

Sing it with us. Portland has Big Pipes.

You’ve probably seen the bulletins during periods of intense rainfall about sewage overflows in the Willamette River. While this stinks, events like this used to happen at a clip of 50 times a year, making our city’s waterways unsafe for most recreation, not to mention the environmental impacts.

Enter the Big Pipe Project, a massive system of underground infrastructure that took 20 years (1991-2011) and $1.4 billion dollars to complete. Thanks to this massive investment, combined sewer overflows (CSOs) on the Willamette River have fallen by 94% and those on the Columbia Slough saw a 99% reduction. Talk about a glow up.

Two kayakers paddle down the Willamette River underneath the Ross Island Bridge in Portland

When a CSO occurs, Environmental Services issues a warning to avoid contact with the river for 48 hours.

Photo by City of Portland

Here are some more interesting facts:

  • The East Side Big Pipe Project is the largest sewer construction project in the city’s history. At 6 miles long and a diameter of 22 ft, you could stack 360 MAX trains end-to-end inside of the tunnel.
  • On average, four CSOs occur every rainy season, with one every third summer.
  • To eliminate 100% of the CSOs, the project cost would have doubled to $2.8 billion.
  • Green infrastructure (trees, rain gardens, and wetlands) help to mitigate the amount of stormwater that is sent to the sewers, as do other cornerstone projects like downspout disconnections.
  • As a homeowner or renter, you can save up to $130 a year with the Clean River Rewards program for allowing rainwater to safely soak into the ground on your property (versus entering city drains).
  • Environmental Services’ tracker provides level updates at 15-minute increments.