The Big Pipe Project, a monumental $1.4 billion investment spanning over two decades, has significantly improved the health of the Willamette River and Columbia Slough by drastically reducing combined sewer overflows (CSOs). With overflows down by 94 percent in the Willamette and 99 percent in the slough, the water quality in these bodies of water is cleaner than it has been for decades.
Before the implementation of the Big Pipe Project, even a minor rain of just one-tenth of an inch could trigger overflows, resulting in an average of 50 CSOs each year that sometimes lasted for days. Today, that number has plummeted to an average of only four overflows per rainy season, with just one occurring every three summers. This remarkable reduction underscores the effectiveness of the project, which was completed in 2011 after two decades of construction.
The Big Pipe Project is not merely a single initiative but part of a comprehensive strategy by Portland’s Environmental Services to manage stormwater and reduce CSOs. This includes various “Cornerstone Projects” aimed at keeping stormwater out of the combined sewer system and the notable Downspout Disconnection Program, which allowed residents to redirect roof drainage away from the combined sewers. By the end of the program, over 56,000 disconnections had been made, preventing 1.2 billion gallons of stormwater from entering the system annually.
Additional efforts included the construction of pipelines to carry clean stream water directly to the Willamette River, as well as the installation of approximately 3,000 stormwater sumps and sedimentation manholes across the city. These installations help trap pollutants and allow for natural absorption into the ground. One of the largest projects, located in the St. Johns area of North Portland, featured new storm sewers and a pipeline that channels stormwater to a constructed wetland known as Ramsey Lake for treatment.
While the results of the Big Pipe Project are commendable, some ratepayers may still question the existence of any remaining CSOs. Eliminating all overflows entirely would have cost at least double the initial $1.4 billion investment, leading to skyrocketing sewer rates for residents. County officials noted that for the additional expenditure, the overall improvement in river health would not have been significantly greater, justifying the current approach.
Today, about one-third of a ratepayer’s sewer bill is allocated to servicing the debt incurred from the Big Pipe Project. This long-term financing model spreads the costs across generations, ensuring that all users of the system—past, present, and future—contribute to its upkeep.
As a leader in river protection, Portland serves as a model for over 800 U.S. cities grappling with similar CSO challenges. Many of these cities are still in the planning or construction phases of their projects. Thanks to the Big Pipe Project, Portland residents have been enjoying a healthier river for nearly a decade, showcasing the effectiveness of strategic investment in infrastructure and environmental health.
