While some places might have only one system into which rainwater flows, our topography and geology make things “uniquely complicated,” says Adrienne Aiona, an engineering supervisor with the city’s Bureau of Environmental Services (BES). Some stormwater enters the combined sanitary sewer system and goes to a treatment plant. Some drains to surface water bodies through a separated system. And some is handled by an underground injection control (UIC) system to infiltrate into groundwater. The more that can be kept out of the combined system, the better.

Rainfall amounts differ across the city, with the West Hills and downtown often much wetter than the airport. But BES’s varied stormwater approaches have less to do with differences in the amount of rainfall and more to do with differences in soil, sediment, slope, and street coverage, all of which affect how quickly stormwater moves and what gets picked up (or filtered out) along the way. 

16 Most consecutive days with at least 0.01 inch of rain recorded in Portland, in January 1970. On January 22, nearly an inch of rain fell in one hour.

72.71 Highest annual rainfall, in inches, ever recorded in downtown Portland, in 1996.

35% Reduction in stormwater volume going into the combined sewer in Portland credited to the city’s green stormwater infrastructure.

$1.4B Total cost of the Big Pipe project.

1.2B Gallons of stormwater removed per year from the combined sewer thanks to more than 56,000 disconnected downspouts.

40 Approximate number of green street installations per year in Portland today.

35% Maximum discount Portland property owners can get on their stormwater portion of their water bill through the Clean River Rewards program, for maintaining such features as ecoroofs, storm basins, and a tree canopy. 

1991 Year the Oregon Department of Environmental Quality set a 20-year deadline for Portland to dramatically reduce combined sewer overflows.

1996 Launch of the city’s Downspout Disconnection campaign, encouraging residents to direct the water from their gutters somewhere other than into the sewer pipe.

1998-99 Several local salmon species listed as endangered.

2006 Completion of the West Side Big Pipe, 3.5 miles long and 12 feet in diameter.

2011 Completion of the even larger East Side Big Pipe, 6 miles long and
22 feet in diameter.

While pro-density housing and building practices carry many environmental and social benefits, they present challenges when it comes to stormwater management, since most of the footprint is built up or paved. “Finding space for stormwater, particularly infiltration, is getting to be a bigger challenge,” Aiona says. If buildings are packed too tightly, rainfall will struggle to find somewhere to go. Suburban areas and new subdivisions planned with a “clean slate” can have an easier time incorporating stormwater infrastructure, Aiona adds. 

Aiona says the region’s hotter, drier summer are taking a toll on the plants in rain gardens, especially ones that have a lined bottom and little shade. “They’re basically like a potted plant in the middle of the right-of-way,” she says. “People who have plants in pots known how often they need water.” She says BES is looking at different soil specs and plant types that can endure effects of climate change while continuing to filter the stormwater that runs through them.

Just like shelter pets and highway sections, storm drains and green streets are available for adoption. About 130 officially registered stewards help weed and remove debris from about 300 green street installations, about 10 percent of the total. Bioswales in high-traffic area or near MAX tracks can’t be adopted for safety and permitting reasons, but plenty more are ready to become part of your family. Even unofficially, people who help clear blockages from storm drains or green street entrances are part of the effort. “The more the merrier,” says Svetlana Hedin, who manages the steward program for BES. “It’s the best way to meet your neighbors.”

Before the completion of the Big Pipe, there were more than 50 combined sewer overflows (CSOs) each year, with heavy rain overwhelming the system and sending untreated, unfiltered nastiness into the Willamette River. Now, there are only a handful. That’s better for all river users, including fish. Fins flap in favor of green street installations, too, where the plants and soil help to slow down and filter runoff from roadways and reduce the amount of car tire toxins (which can be especially harmful to salmon) making their way into river systems. 

Atmospheric river: narrow bands of moisture that can deposit a great deal of rain.

Cloudburst: a sudden, high-volume rainfall, a frequent cause of excess stormwater runoff.

Bioswale: a depression or trench that catches rain and runoff, with plantings that help slow things down and filter pollutants (sometimes called a rain garden).

Green street: a bioswale installation along a road. Infiltration: the act of rainwater soaking into the soil, which helps filter and replenish groundwater.

Sociohydrological: related to the interactions of humans and water. Sump: an underground column for excess stormwater, with perforations for water to seep into the surrounding soil (also called a drywell).

Weir: a construction to raise the water level or alter its flow.