On March 24th the earth moved – under the long stairway leading down from 20th Avenue NE and NE 98th Street to Thornton Creek. The movement shoved the lower section of stairs and collapsed the landing in the middle of the stairway.
The hill above Thornton Creek, on which the stairway is perched, has been the site of previous landslides. Unlike many landslides that suddenly break free and move down hill rather rapidly, the soil at this location tends to move slowly, dropping down near the top and bulging out near the bottom. As a result, in 1986, the city built a large retaining wall along the north side of NE 98th Street. A concrete portion of the stair was attached to the new retaining wall at that time. In 1991, additional landslide activity damaged the timber portion of the stairway which was repaired at that time. In 1996, the soil moved again, again causing damage to the stairway. At that time, SDOT built a more substantial foundation and completely replaced the timber stairway. For the past 15 years the stairway has stood up well. However, following a three-day drenching by Mother Nature, new soil movement pulled the stairway apart again.
Over the past week, SDOT‘s Roadway Structures crew worked hard to repair the stairway as quickly as possible as this is a heavily used stairway. Serving as an important school route for students attending the Sacajewea Elementary School and as a community link, the stairway connects NE 98th Street to NE 102nd Street.
A more costly repair to the stairway is in the future as soon as the funds can be secured. Public safety is SDOT’s highest concern and although we consider this a somewhat temporary repair, it is completely safe, even if there is additional movement of the hillside this year. SDOT Engineers will continue to monitor the conditions at this stairway to ensure the area remains safe.
Seattle Public Utilities does have a project planned that will create a floodplain at this location. While SDOT does not yet know the details of the design and the exact affect this project will have on the existing stairway, the department does know that this important community connection will remain part of Seattle’s pedestrian network forever.