Feb 10, 2015

County studying options on sliding Wapiti road

A portion of Stagecoach Trail near Wapiti appears to be slowly sliding away towards the Shoshone River.

“Really, other than watching it, we’re kind of stumped on what to do with it, really,” Park County Engineer Brian Edwards told the county commissioners last week. For example, trying to armor the river bank below the road would be “a bloody Band-Aid — it’s not going to stop the movement, by any means,” said county staff engineer Jeremy Quist.

This Wyoming Department of Transportation photo shows where the Shoshone River is undercutting the bank.
The area in question is a roughly 700-foot stretch of Stagecoach Trail, not far from where it connects with U.S. Highway 14-16-20, just east of the Wapiti school.

Blame for the shifting soil underneath the county road is believed to lie with an ancient miles-long landslide that began some 10,000 years ago; the smaller so-called “Wapiti Landslide” that’s effecting Stagecoach Trail is on the toe of the bigger landslide complex and is being undercut by the Shoshone River, according to a report from Wyoming Department of Transportation Project Geologist Dave Vanderveen.

The thinking is that the road has been shifting for quite some time — “That thing’s been moving ever since I can remember,” said Commissioner Lee Livingston, a long-time Wapiti resident — but the cracks and sunken areas became more noticeable when the surface was changed from gravel to asphalt in recent years.

The road was re-paved last spring, but cracks had already re-appeared by last month. The plan now is to return that short stretch of the road to gravel, because “we’re basically throwing materials away,” Edwards said.

Commissioner Loren Grosskopf said the county should do what it can to protect its road, noting that the route would be the only way to get to Wapiti and Yellowstone National Park from Cody if the nearby bridge on U.S. Highway 14-16-20 was to fail.

“It seems like we ought to be doing something other than just watching,” Grosskopf said, adding, “I would like to see us start working on options.”

Some ideas suggested during the meeting were to look at moving the road to the south or finding a way to bolster the river bank.

Park County Road and Bridge staff are keeping a close eye on the area and are installing survey monuments to track the earth’s movement. They also hope to come up with a way to protect the road, though, “everything we can think of is a pretty costly solution, if anything, that’s really practical,” Edwards told commissioners.

A Wyoming Department of Transportation map of the area.
In the meantime, staffers have put up signs to slow down traffic in the area and will close the segment if it becomes a safety risk, Edwards said.

County staff had been concerned that the slide area on Stagecoach Trail might dump a large amount of soil into the river — backing it up and causing it to damage the nearby highway bridge. However,
Vanderveen’s report concluded that — while a big slide is a possibility — it’s more likely that smaller amounts of soil will keep shifting.

“It does not appear that the landslide is impacting the bridge,” he wrote.


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