The Washington State Department of Transportation has commenced emergency stabilization work near the summit of Tiger Mountain, amid fears that further heavy rain could cause major erosion.

Department project engineer Dave Lindberg said that the shoulder of State Road 18, near the Holder Creek Bridge, had already cracked.

“If we have additional flooding we could lose the highway,” he said.

“We will stabilize the hillside to protect against further erosion and damage.”

Storms in December and January caused Holder Creek to flood and erode the hillside supporting the roadway.

Lindberg said that a plugged culvert was blocking the flow of water down the hillside.

“The culvert has a large rock in it, and this is causing the water to back up,” he said. “This water has been soaking into the embankment, weakening its structure.”

Lindberg and his team will attempt to remove the rock and restore the proper functioning of the culvert.

He said that they hoped to be able to do this without digging up the road around the culvert, but would do so as a last resort.

The remainder of the work involves building a rock buttress underneath the downhill shoulder of the road.

Workers will also repair the damaged shoulder and guardrail.

Lindberg said that the department is constantly tracking the progress of slide prone areas, to identify potential danger areas, like the Tiger Mountain site.

He said that pre-emptive stabilization was carried out whenever possible, however the funds were not always available for this work.

Drivers on State Road 18 should expect delays during the Tiger Mountain work, which is expected to wrap up in March.

An average of 20,000 vehicles use this stretch of highway each day, including about 3,000 trucks.

“Right now, trucks can use the eastbound truck climbing lane to make their way up the long, steep hill,” said Lindberg.

“During construction, trucks will use the general purpose lane with all of the regular commuters.

“Drivers should allow some extra time for their trips.”

They will also repair the damaged shoulder and guardrail.

At night, drivers can expect both directions of SR 18 to be reduced to a single lane, with flaggers alternating traffic through the work zone.