Natural Security: Portland, Oregon
Integrating Gray and Green Infrastructure
Challenge
As with many older cities in the U.S., Portland has spent decades working to save its rivers and streams from the sewage and stormwater pollution it produces every time it rains. At the root of the problem are the acres of streets, roofs and parking lots that have replaced forests and wetlands as the city developed. Rather than soaking into the ground and replenishing water supplies, the city’s ample rainfall gathers on hard surfaces and flows into the sewer system and local waterways.
Stormwater runoff picks up oil, fertilizers, heavy metals, pathogens and other pollutants as it flows through the city. In addition, much of the city is served by a combined sewer system, which sends raw sewage and stormwater into local waterways nearly every time it rains. This takes a heavy toll on human health and local ecosystems. Nationwide, millions of people fall ill from coming into contact with untreated sewage every year.
Portland’s Approach
In order to solve its stormwater and sewage problems, Portland developed a $1.4 billion plan in 1991 to build new sewer lines and large pipes that can store sewage during storms. More recently the city has turned to small-scale green techniques such as green roofs, swales and downspout disconnections which replicate natural systems such as forests and wetlands by retaining and filtering stormwater. This approach reduces the amount of stormwater that enters sewers, limiting the potential for overflows.
Over the past fifteen years, Portland has offered homeowners a variety of incentives to reduce runoff from their property. The city has also installed swales, rain gardens and curb extensions along streets throughout the city in order to retain and absorb stormwater. In 2008, the city significantly expanded these efforts through its Grey to Green initiative, which will invest $50 million in green infrastructure over five years. This initiative will increase the number of green streets, ecoroofs and trees while protecting undeveloped open spaces and restoring native vegetation.
Benefits
Portland’s efforts are already resulting in significant improvements in the quality of local waterways. Expanded sewer pipes have greatly reduced the number of sewer overflows, and completion of the big pipe system will provide additional improvements. It is still too early to fully assess what effect Portland’s green infrastructure initiatives are having on water quality but early results suggest that they are highly effective in controlling stormwater runoff.
The Downspout Disconnection Program, which provides incentives for homeowners to prevent roof runoff from flowing into the sewer, removes 1.5 billion gallons of stormwater from the sewer system every year. Green Street projects currently retain and infiltrate about 43 million gallons of stormwater per year and have the potential to manage nearly 8 billion gallons, or 40 percent of Portland’s runoff annually.
Furthermore, unlike traditional approaches, green infrastructure provides a host of additional benefits such as groundwater recharge, improved air quality, lower temperatures and more beautiful neighborhoods. They are also more cost effective; in one project, Portland saved $63 million by incorporating swales and trees into a sewer rehabilitation projects.
Adapting to a Changing Climate
While Portland has made significant steps towards addressing its water problems, climate change threatens to reverse some of this progress. As temperatures rise, severe storms that overwhelm the city’s sewer system will grow more frequent and more extreme. Water systems will need the capacity to handle large amounts of precipitation and the flexibility to manage highly variable conditions. Fortunately, Portland’s integrated approach that combines traditional and green infrastructure elements provides the city with the flexibility to weather an uncertain future. Even as storms grow stronger, green infrastructure will absorb stormwater runoff and the attendant pollutants, effectively adding capacity to the city’s stormwater system and preventing a rise in overflows.
Green infrastructure has the added advantage that it is flexible and can be scaled up according to need. Whereas expanding capacity of pipes and treatment plants would be extremely expensive if precipitation patterns exceed historical trends, decentralized green infrastructure projects will allow the city to add new capacity relatively easily by expanding existing initiatives and continuing to embed these techniques throughout the landscape. In addition, because green approaches are more cost effective, Portland will have greater financial flexibility to adapt to climate change with limited funding. This approach will make the city more resilient and will protect public health even as a shifting climate increases uncertainty and creates new challenges.
