natural drainage systemOn Monday, July 22, the Council unanimously adopted a resolution establishing a City policy supporting green stormwater infrastructure (GSI) and adopting a goal of managing 700 million gallons of stormwater annually by 2025 – about 1000 gallons for every Seattle resident. The resolution will be implemented by including green stormwater infrastructure in city projects and encouraging residents and businesses to implement GSI on their property.

Draining stormwater has never been a very glamorous part of City government. For a long time, it just meant building drains and gutters to direct stormwater into the nearest water body, mainly to minimize flooding. Then, in the 1970’s, with implementation of the Clean Water Act, cities discovered that water draining off streets and private properties carried a lot of pollutants. Since then, cities have worked to organize comprehensive drainage strategies to contain and treat stormwater runoff.

But drainage systems are expensive, require lots of maintenance, and can be overwhelmed by large or intense storms. So Seattle has started taking stormwater back to our ‘roots’ by emphasizing the use of trees and vegetated swales to slow down, absorb, and biologically treat runoff.

Major work started in 2001 with the SEA Streets project near Carkeek Park, which created swales to contain the runoff from 2.3 acres. Since then, the City has implemented five other projects, covering 230 acres of Seattle, along with a program to encourage residents to collect and use rainwater. Drainage rates, which used to be a flat fee per property, have been reengineered to be based on the size of lots and provide lower rates to properties that maintain trees and other green surfaces.

There have been problems along the way, most notably a project in Ballard that was poorly designed for soil conditions and never worked properly. And there is a major project underway to treat 630 acres of Capitol Hill that currently drains into Lake Union, removing an estimated 190 million gallons of stormwater annually.

Climate change, the increasing cost of conventional drainage facilities, and a growing population have combined to give the City a new sense of urgency about converting to more green stormwater infrastructure. Seattle has also signed a new Consent Decree for Combined Sewer Overflows that encourages innovative strategies, and our new stormwater permit requires us to update our codes for managing runoff stormwater from developments.

All of these factors combine to make this an optimum time to set an ambitious goal for using green technology to manage stormwater and turn lose the creativity of City planners and the private sector to ensure that it is implemented. The new goal will require expanding rain gardens, roadside swales, green roofs, pervious pavement, stormwater cisterns, and rainwater harvesting, and encourages the use of regulations and incentives to encourage this work. We currently manage only a little over 100 million gallons of runoff annually. By 2025 we hope to make GSI the City standard, and to have reached the 700 million gallon goal and be poised for more in the future.