December 17, 2015
Here’s how your sewer and stormwater system worked during the recent rain storm.
During the December 5-December 13, 2015 rainstorm, the Columbia Boulevard Wastewater Treatment Plant processed an average of 300 million gallons per day. The largest daily volume was 370.8-million gallons on December 7. The treatment plant normally processes an average of 70-million gallons a day.
The plant processed a total of 1.5 billion gallons from December 5 to December 10. That much water would nearly fill 2,271 Olympic size swimming pools.
The heavy rain caused Portland's combined sewer system to overflow to the Willamette River for nearly 16 hours between December 7 and December 9. Outfall pipes discharged more than 638 million gallons of combined sewage to the river.
Intense rainfall also caused a brief combined sewer overflow to the Columbia Slough on December 7. It was the first overflow to the slough caused by heavy rain since the city completed the Columbia Slough Big Pipe in 2000.
The rain was heaviest on December 7 when up to 2.3-inches fell on parts of the city in six hours. Over the nine-day storm event, about 7 inches fell in the outer east side, and about 10.6 inches fell in the northwest part of the city.
Most parts of Portland experienced a 25-year rainstorm, or a storm with a 4 percent chance of occurring.
You can monitor rainfall across the city right along with the control center team at the Columbia Boulevard treatment plant. Environmental Services posts rain gauge data at City of Portland HYDRA Rainfall Network.