Support Us Button Widget

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.

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.
More from PDXtoday
Sponsored
Wherever fall takes you, bring this seltzer to help you chill out.
Sponsored
The can’t-miss week of events includes live science demonstrations, workshops, lectures, food trucks, and unique local vendors.
Sponsored
Sponsored
Reach your local community with our help.
Sponsored
Sponsored
To help make your entire process at PDX as smooth as possible, we’ve created a guide that covers everything from gates and parking to details on the airport’s 70 nonstop flights.
Whew, 2025 is shaping up to be an eventful year in Rose City.