Repairs coming to SR 410 near Crystal Mountain after November debris flow

By David Rasbach

Located just northeast of Mount Rainier, Dry Creek rarely is as barren as its name would suggest, but a rainy start to November left it anything but dry.

Unusually high rain totals during the first five days of November caused a debris flow that changed Dry Creek’s path under State Route 410, causing it to spill over the road. The good news is repairs are on the way.

SR 410 provides vital winter access to Crystal Mountain Resort and in the summer serves travelers heading to Mount Rainier National Park or over the Cascade crest on Cayuse and Chinook passes.

After considering a variety of options, we developed a two-part plan that will allow for repairs without full closures of the highway during peak ski season while protecting the highway during spring snow runoff. The first part of the repairs will involve single-lane closures with alternating traffic in late February, allowing us to hold off on a full closure of SR 410 until later in the spring or summer.

Debris flow

During the first five days of November, about five inches of rain was recorded at the Corral Pass weather station near Dry Creek. That’s five times the 10- and 20-year averages for those dates according to records collected by NOAA’s National Centers for Environmental Information.

On Nov. 4, alone, the Corral Pass station recorded a whopping 3½ inches of rain, soaking the area that Dry Creek drains. Part of Dry Creek’s watershed includes a large burn scar left by the 2017 Norse Peak Fire, which burned tens of thousands of acres.

Up to two feet of debris covered SR 410 near Crystal Mountain Resort after a Nov. 5, 2022 debris flow caused Dry Creek to change channels and plug
a small culvert under the highway.

There was simply too much water for the saturated ground in the area to retain, and early Nov. 5, a debris flow of mud, trees, rocks and sediment broke loose and rushed down Dry Creek.

There are two historical channels that cross SR 410 about two miles before the turnoff to the Crystal Mountain Ski Resort and 12 miles up the hill from Greenwater, and Dry Creek traditionally flowed through the south channel.

As the debris flow gained momentum through the Dry Creek channel, massive trees and rocks plugged the creek’s path about 600 feet above SR 410, forcing the debris flow to find a new route as it rushed downhill. With the south channel literally filled to the brim, Dry Creek jumped into its older, unused north channel and roared toward SR 410.

A huge rain storm this past November overwhelmed culverts and the hillside, leading to debris covering SR 410 near Crystal Mountain Resort.

The flow overwhelmed and plugged a small culvert placed at the crossing of the north channel, causing water and up to 2 feet of debris to spill across the road and forcing us to close the highway for several hours. Emergency crews and highway engineers inspected and cleared the road leaving Dry Creek to flow through a 24-inch culvert instead of the 4-foot culvert a few hundred feet up the highway along its previous path.

Dry Creek’s new path

Though sediment and water did scour the embankment on the west side of the highway, our inspectors found SR 410 fared rather well. Maintenance crews built the embankment back up and stabilized and cleared the road, allowing it to reopen.

While operations along SR 410 essentially returned to normal, the same cannot be said for Dry Creek. A debris dam of trees and boulders – more than 50 feet high in some places – still prevents the creek from flowing through its previous path to the White River below.

“All of Dry Creek is now running to that smaller culvert,” Project Engineer Cullen Anderson said. “These colder months, I think we’ll see some stability there because everything is locked up in snow and ice.

“But as soon as we get to the spring melt, which based on nearby gauges looks like it occurs in March and gets really ramped up in April, you’re going to see all that snowmelt being conveyed to that culvert, and it’s very, very likely that we could have a similar if not more extreme event, where once that culvert gets plugged, all that runoff will back up and start coming over the roadway.”

SR 410 near Crystal Mountain closed this past November after a large rain storm caused debris to cover the highway.

That could trigger more serious problems, including more scouring of the embankment and damage or loss of the road, which is the only way in and out of Crystal Mountain Ski Resort when Cayuse and Chinook passes close for the winter.

Removing the debris dam to allow Dry Creek to return to its previous channel is not an option, as it would take large excavators and other heavy machinery cutting a path through several hundred feet of thick forest to reach the dam and clear the now-fully-filled former stream bed. Additionally, the dam is located well outside our right of way on U.S. National Forest land.

“That leaves us with the option of trying to increase the capacity of the culvert in order to be able to convey the flow heading to it,” Anderson said. “That’s what we’re working on right now is designing a culvert that can go in quickly that will convey all the runoff through this area.”

That means excavating a 100-foot stretch of the highway, installing a 10-foot culvert and rebuilding the road. It is expected that work will require a three-day full closure of the road. Once that work is done and SR 410 reopens, crews will regrade Dry Creek’s channel and rebuild and armor the embankment.

A debris flow this past November along Dry Creek overwhelmed a 24-inch culvert under SR 410 near Crystal Mountain Resort, causing water and about two feet of debris to cover the highway. It also caused scouring along the shoulder and embankment.

Finding a solution

With the spring thaw just around the corner, our engineers have considered several concepts to make the needed repairs, fully aware that skiers, winter sports enthusiasts, local businesses and residents depend on that section of SR 410 during the winter.

After examining different options of how to reduce the effect of a full road closure, we decided to break the emergency project into two parts.

A debris dam of rocks, trees and sediment about 50 feet high plugged Dry Creek’s channel after a November 2022 rainstorm. It permanently changed
the path of the creek under SR 410.

The first will need to be done in late February and involves inserting three 24-inch overflow culverts a few feet beneath SR 410 to divert any excess runoff beyond what the existing culvert is capable of handling. Work on this portion of the project should be mostly completed while closing only one lane at a time, allowing alternating traffic to pass.

The hope is that the additional culverts will provide a safety measure to prevent an incident similar to what occurred last fall. That should allow the second portion of the project – the part that will require three days of full closure of SR 410 to insert a larger, more permanent culvert deeper under the highway – to proceed after peak ski season later this spring or summer.

Though Mother Nature controls when the highest spring runoff will be, we plan to complete the project before traffic along SR 410 picks back up with the opening of Chinook Pass, which typically occurs in late May.