Movement slows on steep Peaceful Valley hill after city works to prevent landslide

Engineers continue to monitor a Browne’s Addition hillside’s potential descent into Peaceful Valley, but a long-term solution likely remains weeks away.

The city has pledged to fast-track its work to devise a plan that will permanently fortify the hill between the two neighborhoods.

In the meantime, recent cold weather helped freeze moisture inside the soil and slow its movement, allowing crews time to build a berm that should offer more support.

“That berm is in essence shoring that (retaining wall) up in order to push back against the slide,” explained Kyle Twohig, the city’s director of engineering. “We also haven’t seen any indication of additional slide movement up higher on the hillside.”

Those two factors make city officials confident that nearby buildings, including those atop the hill on Riverside Avenue, aren’t at risk.

The encroachment of the Browne’s Addition neighborhood into Peaceful Valley below was first noticed in the wake of a powerful January windstorm, which destabilized trees on a hillside already saturated by heavy rains.

Days after the storm, a tree on the hillside toppled onto nearby power transmission lines, causing much of Browne’s Addition and Peaceful Valley to lose electricity service for the night. Crews have since worked to remove dangerous trees from the hillside.

The city quickly called in a geo-technical engineer to assess the situation.

“The challenge is to try to abate the movement as best as possible, combined with the tree removal we had to do, because we had trees falling on power lines and literally trees sliding down the hill,” Twohig said.

Since then, engineers have monitored the soil’s movement. The city has not evacuated nearby homes, which it does not believe are at risk. Much of the land in the immediate vicinity of the hillside is vacant.

The roadway below is a different story, however.

The city buttressed the retaining wall at the corner of Clarke and Elm Street hoping to prevent a collapse, but Clarke Avenue will remain closed near Elm Street for the foreseeable future. Even after the unsafe hillside is addressed, the road will likely be shut off because it will be the site of construction of the South Gorge Trail.

The city hopes to have a drill on the site as early as this week, which will bore dozens of feet beneath the surface and allow engineers to analyze the layers of soil below.

“We still have to get in and do our subsurface investigation, so that is going to come up next,” Twohig said. “What that will do is feed the information we need to design a solution.”

Anecdotal evidence of the hill’s instability dates back decades, according to Twohig, including movement in the 1950s and the 1980s during weather events.

“It could be that this hillside has actually moved every 30 years or so,” Twohig said.

The cost of the entire effort could amount to more than $1 million, according to the city.

City Spokesman Brian Coddington said the city will provide regular updates to the surrounding neighborhood regarding the project’s progress.