More than three inches of rain have fallen in Portland since Friday, but it hasn’t been enough to cause overflows from Portland’s combined sewer system. Before the city completed the $1.4-billion combined sewer overflow (CSO) control program in November 2011, only one-tenth of an inch of rain in 24 hours caused a CSO. In those days, the recent rainfall would have filled combined sewers to capacity and millions of gallons of combined sewage to would have overflowed to the Willamette River.
Today, Portland’s east side and west side big pipes collect combined sewage that once overflowed during rain storms. The tunnel system filled to about half-full on Friday and Saturday and was 83% full on Monday.
“Portland’s ratepayers made a significant investment in the Big Pipe to keep sewage out of our river,” said Commissioner in charge Nick Fish. “The last few days of heavy rains tested our system, and I’m pleased that it worked exactly as it was designed to.”
Portland’s green stormwater management infrastructure works with the CSO control system by keeping stormwater runoff out of the combined sewers. Green infrastructure facilities, including green streets and ecoroofs, manage an estimated two-billion gallons of stormwater annually in neighborhoods with combined sewers.
The CSO control program included expanding treatment capacity at Portland’s Columbia Boulevard Wastewater Treatment Plant. The plant successfully treated recent high flows the heavy rains created, despite periods of wastewater entering the plant at a rate of 400 million gallons per day.
This kind of wet weather also once caused flooding along Johnson Creek about every other year. But the creek stayed within its banks during the recent heavy rains.
The city finished work on the Foster Floodplain Natural Area in 2013 along Foster Road between SE 104th and SE 111th avenues to add 120 acre-feet of flood storage. That’s enough to cover the 63-acre site with about two feet of water. The floodplain project reduces Johnson Creek flood frequency to about every six to eight years.
For more information contact Linc Mann, 503-823-5328.
The Bureau of Environmental Services provides city residents with Clean River programs including, water quality protection, wastewater collection and treatment, and sewer installation.