Green Stormwater Infrastructure Alternative in Washington

This past Friday was a milestone for Washington’s Puget Sound water quality.  The Department of Ecology is proposing new development rules to mitigate and control polluted runoff, so that stormwater from roads and roofs can be treated naturally rather than burdening, often inadequate,stormwater infrastructure.  December 31, 2016 marks the last day 110 local governments in Washington have to update their development codes to reflect the Department of Ecology’s standards for low-impact development.  Over the next four years, municipalities will test the feasibility of various low impact development strategies before implementing their new stormwater management code so to avoid unintended consequences:  unneccesary ponding, basement flooding and potential landslides that may occur when stormwater does not drain.  Robert McClure reports on the proposal with thoughts to debate from both developers and environmentalists in his article “Developers to Legislature:  Save us from runoff rules” on February 1, 2012.

As a counter-initiative to the proposed stormwater code changes from the Department of Ecology, on the table in Olympia is HB 2641, a bill designed to eliminate the requirement for low-impact development and replace it with voluntary initiatives that incentivize cities and developers.


Seattle has been a leader in the state and the country for low impact development and as all responsible organizations do, is once again revisting and revising its stormwater code which currently requires Green Stormwater Infrastructure (GSI) to “the maximum extent feasible”.  A term that many find elusive and confusing with far-reaching effects and does not allow authorities to clearly enforce any GSI and natural drainage strategies.

According to the city of Seattle, “natural drainage systems limit the negative impacts of stormwater runoff by redesigning residential streets to take advantage of plants, trees, and soils to clean runoff and manage stormwater flows.  Vegetated swales, stormwater cascades, and small wetland ponds allow soils to absorb water, slowing flows and filtering out many contaminants.” Bioswales and Rain gardens have been shown to reduce the number of homes experiencing basement flooding during heavy rain events.  Green roofs can be an effective way to treat roof rainwater, though are typically more expensive than other alternatives.

Here’s a brief summary of City of Seattle natural drainage case studies:

Seattle’s Natural Drainage Alternative Programs:

Street Edge Alternatives:  Seattle completed a pilot project in 2001 that reduced impervious surfaces 11% from a typical street and added 100 evergreen trees and 1,100 shrubs.  As a result, the street runoff has been reduced 99%.


Ballard Roadside Raingarden:

Ballard is an area of interest because of two uncontrolled CSO basins.  There are approximately 15 overflow events in this basin per year, exceeding the EPA’s allowance of just one overflow per site per year.  As a less costly and natural alternative to expanding and retrofitting existing sewer infrastructure, the Ballard Roadside Raingarden project is an example of stormwater retrofits in the right of way.  While the project has had successes, it has received much criticism for its troubles.  At some of the installed raingardens, soil inadequately drains and ground water just below the surface contributes to the excessive ponding.  Seattle Public Utilities has been maintaining all the raingardens in the right of way for the natural drainage projects.

In our next Blog post, we will explore the opportunities and challenges for you the home or business owner.