A rainstorm that resulted in flooding throughout Portland also caused stormwater and sewage to be dumped Wednesday morning into the Willamette River.
But it would have been much worse without Portland’s Big Pipe project, which was designed to reduce these overflows, said Diane Dulken, public information officer for the city’s Bureau of Environmental Services.
“For years and years when it rained, sewage flowed into the river,” she said. “Now it’s so rare that when it does happen it’s news.”
The 20-year project, which cost $1.4 billion, was completed in 2011.
Dulken said the system refers to a series of improvements, from disconnecting downspouts on homes to allow rainwater to be absorbed naturally in the ground, to the construction of big pipes on both sides of the river and along the Columbia Slough to store and convey large quantities of flows to the city’s main wastewater treatment plant in North Portland.
Before the system was completed, she said, sewage flowed into the Willamette River an average of 50 times a year, with overflows lasting days.
Today, overflows occur an average of four times per winter season and once every three summers.
This is the fourth overflow of the year.
As of noon Tuesday, the Big Pipe system had captured and prevented about 300 million gallons of diluted sewage from reaching the river since this week’s series of storms began.
There is no estimate for Wednesday’s overflow, still ongoing, that affects the stretch of the river downstream of Sellwood Park.
During an overflow and for 48 hours after an overflow stops, the public is advised to avoid contact with the river because of increased bacteria in the water. The river’s water quality is safe for recreation during all other times.
“The system transformed our relationship with the Willamette River,” said Dulken. “It’s doing what it was designed to do. It takes a big event to trigger an overflow, and that’s happened.”
— Tom Hallman Jr
503-221-8224; thallman@oregonian.com; @thallmanjr
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