Thursday – Sunday, October 13-16, 2016
A lot of rain citywide
Strong rain showers crossed the city starting Thursday, October 13, and continued through the weekend. Over 1.6 inches of rain fell across Portland on October 13, and more rain fell on Friday, October 14, with parts of the city receiving 1.00-1.26 inches in just an hour. By comparison, the rainiest hour recorded at PDX since 1951 only produced 1.03 inches.
All of that rain nearly filled the Willamette River Big Pipes, which reached 99% capacity but did not overflow. The Westside Big Pipe is 14 feet in diameter and 3.5 miles long, while the Eastside Big Pipe is 22 feet in diameter and 6 miles long. The Big Pipes safely conveyed all the wastewater sent to them from other parts of the system to the Columbia Boulevard Wastewater Treatment Plant in North Portland.
Two combined sewer overflows (CSO)
Two combined sewer overflows for a total of about 830,000 gallons did occur, however, because a pump station and an upstream collection system were not able to send their flows to the Big Pipes during particularly intense rainfall Friday night. These two CSO events were the second and third of 2016. Before we completed construction of the Willamette River Big Pipes in 2011, we had an average of 50 CSOs each year. Now we have an average of 5 each year. For more information about CSOs, what they are and why we still have them, click here.
Wastewater Collection and Treatment
Since Monday, October 10, the treatment plant processed well over 1 billion gallons (1,062,767,000), which is more than twice a normal week. Prior to the Big Pipes being built, this was not even possible. The treatment plant processed almost 240 million gallons on Thursday, 202 million Friday and 251 million Saturday. It typically treats 70 million gallons a day.