Crown Hill GSI (Green Stormwater Infrastructure)

Project description

Green stormwater infrastructure uses special soils and plants to capture rainwater, clean it, slow it down, and soak it into the ground.

Project background and updates

In summer 2023, the SPU team conducted “options analysis” (OA) outreach with the community to introduce potential design elements and hear concerns, impacts, and ideas from the public about the Crown Hill GSI Project (formerly 17th Ave NW Stormwater Improvements). Thank you for your participation and thoughtful comments! Hearing from various perspectives – whether you commute through the neighborhood or are a resident on one of the project blocks – was incredibly valuable to us.

Our project team is currently in the early design phase. SPU has incorporated feedback from the community, permitting agencies, and other impacted parties into the current design. We will continue to engage with the community through the design and construction phase of the project. We will be sharing design concepts and updates on this project website.

What is green stormwater infrastructure (GSI)?

Green stormwater infrastructure (GSI) is a built system designed to mimic natural environments by slowing and filtering stormwater. When rain falls in urban settings it runs fast off hard surfaces like roofs, streets, and parking lots and cannot be absorbed efficiently into the ground. GSI systems typically rely on a mix of vegetation, special soils, and other natural features to reduce flooding and clean water before it goes into the sewer system or larger critical water bodies. Green stormwater infrastructure can include roadside rain gardens and street trees.

Reducing street flooding and sewer problems in Crown Hill by building natural drainage systems

Some parts of the Crown Hill neighborhood experience street flooding or sewer backups. The project will address the area with the largest and most frequent flooding problems.

Flooding and sewer problems happen during rainstorms on 17th Ave NW because runoff from a large upstream area hits undersized, shallow pipes under the street. When the pipes fill, water bubbles up from inlets and ditches overflow into the intersection. Because the pipes are full, there’s nowhere for water to go until the system drains. A challenge for fixing the problem is that blocks downstream from the project area also experience flooding and sewer risks — if SPU were to simply increase the pipe sizes on 17th, it could worsen the downstream problems.

This project will use a mix of pipe improvements and aboveground natural drainage systems to improve drainage while protecting downstream blocks. This will take pressure off the system and help it handle larger storm events.

Location

The project will focus on the area between NW 90th St and NW 85th St. Most of the work will be along 17th Ave NW with some improvements on NW 87th St and NW 90th St.

Crown Hill Project site diagram. Click to enlarge.

Community benefits

17th Ave NW is an important connection for students walking to and from Whitman Middle School. In wet weather, drainage problems make this route harder to use.

This project will significantly decrease the frequency of street flooding, a long-standing community concern. It will also decrease the risk of sewer backups to some homes on 17th Ave NW, and seek to address priorities from the City of Seattle’s recent community planning process, including the residents’ desire for pedestrian improvements and traffic calming on 17th Ave NW. Finally, increasing system capacity will help accommodate future growth. 

Additional community benefits from green stormwater infrastructure

• Plants and trees installed can create a sound buffer and reduce noise pollution
• Greenspaces help combat the heat island effect (hot sidewalks) by reducing surface and air temperatures
• Vegetation can absorb pollutants and trap airborne particulates making the air cleaner
• Vegetation attracts natural habitat for birds and wildlife that can improve mental health and reduce anxiety

Community involvement

We're committed to providing timely information and updates on project activities. Updates may be available in multiple formats: this website, emails, drop-in sessions, briefings, and/or public meetings. There will be several opportunities for the public to engage and provide feedback during this process.