Green Infrastructure in the Emerald City

By Alex Murray

This is the first of a series of blog posts written by students from the University of Chicago Environment Agriculture & Food Working Group as part of MPC’s research project on stormwater incentive programs.

“Does it really rain that much?” is reliably the first question I get when I tell someone I’m from Seattle. It’s no surprise that, given its reputation, Seattle is on the leading edge of stormwater management. Seattle’s push for green infrastructure solutions to stormwater began two decades ago, driven by the mandates of the Clean Water Act and concerns for the health of the endangered salmon population.

In 2001, Seattle set a national precedent with its Street Edge Alternatives program for the installation of green stormwater infrastructure in public. The combination of sloping bioswales (to filter out harsh pollutants like motor oil), porous paving and the downhill curvilinear shape of the street (to slow water down and redirect it off the pavement) contributed to an impressive reduction in runoff. The project was not only popular with neighborhood residents for its meandering river-inspired design, but decreased the total volume of stormwater runoff by a remarkable 99 percent.

The original Street Edge Alternatives Street retrofit (2nd Ave NW) (from City of Seattle)

Since then, the city has expanded its efforts to include the RainWise residential incentive program for green stormwater infrastructure installation, targeting corridors with high impact on the local watershed and areas most prone to flooding. This approach aims to increase water quality through better control of combined sewer overflows (much like the ones we experienced here in Chicago a few weeks ago). Through the program, homeowners in the city’s targeted regions can apply for rebates on landscaping retrofits (rain gardens) and rain barrel installation. After site testing and approval, the homeowner signs an agreement to maintain the new green stormwater infrastructure features on their property.

In order to achieve stormwater mitigation to the maximum extent feasible, Seattle has set out to “divide and conquer.” Working with residents and businesses, the city initiated natural drainage system partnerships in sidewalk planters in target neighborhoods. Using public dollars, the city has converted parking lot islands and neighborhood planters to bioswales and rain gardens in order to reduce runoff. In these partnerships, property owners can choose to maintain the gardens directly adjacent to their property, marginally cutting down city maintenance costs. Many homeowners like what they see, and choose to adopt some green infrastructure techniques on their own properties for both aesthetic and functional purposes.

Seattle Public Utilities performs routine maintenance checks on these natural drainage system installations to ensure they continue to operate effectively. These partnerships blur the line between public and private green infrastructure investment, and help the city meet its runoff reduction targets while increasing the visual appeal of the neighborhood.

This year, Seattle renewed its commitment to green infrastructure with an executive order from Mayor Mike McGinn to reduce annual runoff by 700 million gallons (six times the number currently managed by green infrastructure in the city) by the year 2025.

To that end, the city has taken a multifaceted approach in considering how to increase stormwater mitigation over the next decade. The proposed TDR for TIF (Transfer of Development Rights for Tax Increment Financing) program does just that by aligning the city’s stormwater goals with plans for urban density. Developers who wish to build in selected downtown zoning districts can receive a density bonus if they also purchase rural land development credits.  The density bonus allows the developer to build more units per floor, increasing their overall revenue. Developers qualify for this incentive if they choose to purchase the rural land credits within the county (the “transfer of development rights” part of the program).

These land credits ensure that forested land remains undeveloped in the future. The undeveloped forestland is naturally able to absorb rainfall much better than impervious developed land. This aspect of the program helps to ensure that the regional watershed remains protected in the years to come.

Schematic diagram of TDF for TIF Program (King County, WA)

On the urban side, the increased property tax revenue from the density bonus is invested in green infrastructure installation in the selected downtown zoning districts. This is the “tax increment financing” part of the program. Put together, the program as a whole helps to manage stormwater in both urban and rural areas. Through this new program, the city hopes to encourage downtown development while maintaining water quality and mitigating runoff through stormwater-conscious urban development and the preservation of rural land.

Dynamic programs like these have turned Seattle into a sort of stormwater sponge, and will be an integral part of the effort to meet the target the city has set for runoff reduction over the next decade. As both a functional tool for stormwater management and an investment in aesthetic value, green infrastructure has proven its worth to Seattle, rain or shine (but mostly rain).