Retaining wall along Rainier Ave S! Photo Credit: SDOT. Summary
- Seattle’s wet winters, steep hills, and landslide-prone geology make it prone to frequent landslides in the winter and early spring.
- Landslides are more likely when soils are very wet, and many occur within a few days when we have a heavy rainfall or rapid snowmelt.
- A recent project along Rainier Ave S sought to address the landslides along segments of Rainier Ave S from S Carver St to the south City limits near S Ryan St.
- In 2016, we installed a 60-foot segment of retaining wall and cleared overgrowth from the existing sidewalk to open it up to people walking and rolling.
- In 2020, we installed eight retaining walls.
When we envision the natural events that occur in our region, landslides don’t often come to mind immediately. We often mention earthquakes and seismic resilience, sometimes flooding, and definitely inclement weather and its effects on safety and mobility. However, Seattle’s wet winters, steep hills, and landslide-prone geology make it prone to frequent landslides in the winter and early spring.
Landslides are more likely when soils are very wet, and many occur within a few days when we have a heavy rainfall or rapid snowmelt.
The most common landslides in Seattle are shallow (less than 6-10 feet deep) and fast moving (up to about 37 miles per hour), and occur on undeveloped hills – large or small. Landslides can be very destructive to property and infrastructure, and can trigger other hazards like flooding and hazardous materials incidents. Landslides are difficult to respond to especially when they’re triggered by an event – like a winter storm – which can also cause flooding.
As a City, we lessen your and your neighbors’ vulnerability to landslides. This work includes taking inventory of and mapping areas prone to landslides, stabilizing building sites during construction, educating the community, and undertaking stabilization projects, like installing retaining walls, in partnership with private property owners.
We maintain almost 600 retaining walls, and most protect public streets. If all of our retaining walls and seawalls were lined up end to end, they would extend for 21 miles!
A recent project along Rainier Ave S sought to address the landslides with retaining walls along segments of Rainier Ave S from S Carver St to the south City limits near S Ryan St. Over the years, these landslides encroached onto the sidewalk and – in some cases – into the bike and vehicle lanes.
An area prone to landslides along Rainier Ave S, before a retaining wall was replaced & sidewalks were improved. 
After the retaining wall was replaced.
In 2016, we installed a 60-foot segment of retaining wall and cleared overgrowth from the existing sidewalk to open it up to people walking and rolling.
In 2020, we installed or replaced eight retaining walls – called Soldier Pile Walls, Ecology (Eco) Block Walls, and Rock Walls – outlined within the map below.
