County repaving portion of Lower River Road that’s been sliding into river

Posted on September 13, 2024 by Jenn Rowell

A section of Lower River Road will be closed Sept. 16-18 while the road is paved, weather dependent.

Cascade County contracted with United Materials to modify this section of the road, near the marina.

The section is about 1,000 feet that is currently gravel. United Materials will compact and grade the gravel then top it with four inches of new asphalt that will tie into the existing asphalt on the road, according to county public works.

During paving, the section of road will be closed to through traffic and both ends of Lower River Road will have detours setup. Drivers are asked to be aware of signs, workers, detours, road closures and posted speed limits.

County public works has been working on this section of road for several years.

County approves contract for further investigation of Lower River Road slide area

In July, commissioners approved a $78,700 contract to United Materials for the paving after public works and local engineers completed their review of the failing section of the road.

They determined that to permanently fix the section of road that continued sliding into the Missouri River could cost $3 million to $6 million.

“Until the county can decide to make these repairs and save up these funds, the county will be converting this section of Lower River Road back to asphalt,” Les Payne, county public works director, said in the staff report.

United Materials made this change to the Lower River Road in 2018, 2019 and 2023.

In October 2023, commissioners approved a $25,551.50 contract to Big Sky Subsurface to continue geotechnical investigations for the Lower River Road slide area.

County public works has been working with local engineers since 2018 to collect data and help determine the cause and fixes for a section of Lower River Road to keep it from continuing to slide into the river.

In 2021 and 2022, the area began to move and slide at a fast pace than years prior, according to county public works.

County studying landslide area on Lower River Road

That led to county officials meeting with local engineers and in 2022, determining that the county needed to switch the section of asphalt back to gravel for easier maintenance and to save taxpayer money rather than continue to pave the road and have it slide and sink into the river, according to county public works.

In the spring of 2023, the county converted that section of road back to gravel.

The county is looking at a roughly 1,000 foot stretch of Lower River Road, north and west of White Bear Island.

County officials determined that to determine a long-term solution, they needed more research and data, including a river survey.

Earlier this year, the county and Big Sky Civil conducted the survey and passed the data to Big Sky Subsurface of Belt for further analysis, according to county public works.

Les Payne, county public works director, said in October 2023, that he asked Big Sky Subsurface to provide an engineer’s estimate for the final geotechnical investigations and long-term solutions for fixing the road.

In the spring of 2023, public works said the slow-moving landslide is gradually undermining the roadway creating deformations in the roadway’s riding surface and that pavement deformations have been an ongoing issue for many years with continued past efforts to maintain the roadway profile.Without continual maintenance, the landslide would likely progress to a point where the deformations in the roadway could become hazardous to the traveling public, particularly if travel speeds are excessive, and the county is exploring options to identify possible long-term solutions, according to public works.