Whitefish plans to reconstruct the southern most portion of Central Avenue in continued efforts to curb slumping of the road into the Whitefish River.

City Council last week approved a plan that would create narrow two-lane around the curve where the street turns into Sixth Street. By reducing the pavement width to 22 feet and bringing the guardrail in closer to the edge of the curve, the roadway will be reduced by about 6 feet.

The city has for years been monitoring the south end of Central Avenue and though it has been repaired before, the street continues to slump toward the river.

Historically, the area has experience past slide activity extending back as far as 1934, but it’s been 22 years since the last project was completed there.

“There are clear signs of slope instability, which is evidenced by the current asphalt condition and movement of the guardrail,” said Public Works Director Craig Workman. “There are significant safety concerns for vehicles traveling this section of Central Avenue and city staff has been working on solutions.”

Under the approved plan, painted areas in both directions would create bike areas within the traffic lanes and the existing sidewalk would be improved to manage pedestrians.

Workman said the fix would reduce the mass and loading on the slope estimating that it would give the section of road another 20 years before it would need to be reconstructed again.

“We will see continued settlement of the road,” he said. “While this solution will not eliminate future roadway maintenance from soil instability, it strikes a balance between meeting the needs of the neighborhood, improving the existing safety concerns and reducing future maintenance needs.”

The estimated cost for the reconstruction to a narrow two-way road is $345,900, in addition to design costs.

The city had entertained two other options for slumping section — closing that section of the road entirely at a cost of $323,000 or reducing the size of the pavement to one-way traffic heading north only at a cost of $369,400.

Workman said the option to make the section one-way would have likely been a 50-year fix for the road.

“While that option has a longer life, it doesn’t strike a balance between repairing the road and significant safety concerns over access from home and business owners there.”

Property owners to the south told the city that creating a one-way would reduce access to their property, and owners to the north were concerned about changes in traffic flow and potential increased traffic on East Fifth Street as a result.

In addition to addressing the slump area of Central Avenue, the city also plans vehicular, drainage, parking and pedestrian improvements along East Sixth Street from Spokane Avenue to Central, as well as resurfacing Central from Fifth to Sixth.

The slope was reconstructed utilizing structural gravel fill in 1986 as part of a sewer system improvement project. About 10 years later signs of movement in the form of pavement failure and open fractures on the slope were observed. At the time, according to the city, a geotechnical investigation was performed and it was deemed that the failure was caused by overloading the slope.

In 1997 the structural gravel fill was removed with lightweight fill material consisting of wood fiber extending to a depth of about 15 feet.

The city has $400,000 budgeted for engineering and reconstruction of that portion of Central Avenue in the fiscal year 2019 budget. Project costs would be split evenly between the tax increment finance fund and the street fund.