Stormwater Code

Green Stormwater Infrastructure (GSI) includes stormwater best management practices (BMPs) designed to reduce runoff from development using infiltration, evapotranspiration, and/or stormwater reuse. To be considered Green Stormwater Infrastructure, it must provide a function in addition to stormwater management such as water reuse, providing greenspace and/or habitat in the City. Examples of green stormwater infrastructure include trees, bioretention facilities, rain gardens, permeable pavement, vegetated roofs, and rainwater harvesting.

In the stormwater code, all Green Stormwater Infrastructure are considered On-site Stormwater Management BMPs and can be used to comply with the On-site Stormwater Management Requirement, Minimum Requirements for Flow Control, Minimum Requirements for Treatment, or all three, depending on how they are designed and constructed. All projects are required to implement On-site Stormwater Management BMPs to the maximum extent feasible for flow control and water quality treatment. This means that On-site Stormwater Management BMPs must be incorporated throughout the project site wherever feasible, constrained only by the physical limitations of the site and practical considerations of engineering design and necessary business practices.

City of Seattle Stormwater Code and Manual
The City of Seattle’s Stormwater Code contained in Seattle Municipal Code (SMC) 22.800-22.808 requires projects to implement On-site Stormwater Management BMPs, which include Green Stormwater Infrastructure.

Right-of-Way Improvement Manual
The Right-of-Way Improvement Manual, Chapter 4.17, provides information on rules specific to the use of GSI Facilities within the Right-of-way (ROW).