Big Pipes Stop Sewer Overflows


In a year where good news seems scarce, Portland may reach a historic milestone for Willamette River water quality. The year 2020 is on track to be the first in modern history with zero combined sewer overflows to the river.

That’s a triumph of Portland’s investment in the Big Pipe Project, the $1.4 billion 20-year-long public infrastructure project that dramatically reduced such incidents and changed Portland’s relationship with its river. Overflows that used to be common - occurring about 50 times a rainy season, sometimes for days on end - now are rare. Environmental Services projects about four overflows per rainy season, a 94 percent reduction.

Still, the river has never experienced a zero-overflow year before or since the Big Pipe completion in 2011.

“The Big Pipe Project continues to make a big difference,” said Environmental Services Director Michael Jordan. “We enjoy the benefits every day of a river clean enough to swim, paddle, and play. The result of our investment is that river recreation has soared, and river water quality has vastly improved for people and wildlife.”

The year’s not over? Portland right now can celebrate a 16-month streak and counting.

The last overflow was August 2019, a 15-minute incident from a single outfall near Sauvie Island from a hyper-local storm. The last overflow that affected Portland’s entire stretch of the river was in April 2018.

The Big Pipe Project is named after its main features - two giant pipes that absorb sewage and stormwater during rain storms and send that mixture to the city’s treatment plant. It took a generation to build - 20 years - and included many related projects, from nature-based solutions such as rain gardens and disconnecting home downspouts to let soil and plants soak up rain, to complex new pipes and pumping systems. In addition to the Willamette River big pipes, a similar pipe along the Columbia Slough has reduced overflows by 99 percent.

Environmental Services plotted the last big storm, which peaked on November 13. Before the Big Pipe Project, that rainfall of over an inch of rain in 12 hours surely would have led to an overflow. Instead Big Pipe levels never reached above 51 percent, leaving plenty of capacity and keeping the Willamette River sewage-free.

Source: Portland Bureau of Environmental Services