All lanes are now open again on the Highland Park Way hill between West Marginal and SW Holden, two days after the latest landslide. Last night we reported on the SDOT/Seattle Parks plan for erosion control to deter recurrences. Today we asked SDOT about what was done after the February 2017 slide that closed the hill for two days.
Five months after that slide, we reported on City Council funding for a planned “rock buttress” in the area. We don’t have a record of what happened after that, so we asked SDOT. Spokesperson Ethan Bergerson confirmed that the pre-existing concrete blocks south of the recent slides are part of the measures taken after the 2017 slide:
The landslides this past week have occurred at another location to the north of the 2017 landslide. Because Highland Park Way travels alongside about half a mile of the West (Duwamish) Greenbelt without connecting to any other roads, both landslides resulted in the same stretch of road being closed even though they occurred on different slopes.
In 2017, there was a large landslide to the south of where the landslides occurred this past week, which resulted in Highland Park Way SW being closed for multiple days. Seattle Department of Transportation (SDOT) and Seattle Parks and Recreation (Parks) worked together on erosion control measures in this location. Parks crews installed permanent erosion controls and planted native plants on this part of the slope in spring 2017, and SDOT crews returned in the summer to install a concrete block wall with a rock buttress to stabilize the base of the slope (the rocks are behind the concrete blocks and can’t be seen from the street). The steep slope in this location has been stable since then.
This week, SDOT crews installed over 60 feet of concrete blocks as a temporary measure. Parks is also planning to perform additional temporary erosion control measures, and both agencies are planning to return in the spring to install more permanent measures which can only be done when the ground is not so saturated with water.
The area has long been slide-prone; the 2000 Seattle Landslide Study has multiple references.