Little Cottonwood Canyon reopens following rockslides

By Andrew Adams  |  Posted Jul 5th, 2013 @ 5:35pm

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LITTLE COTTONWOOD CANYON — The road through Little Cottonwood Canyon appeared to be in relatively good shape Friday night after reopening following rockslides and mudslides that closed it Friday morning.

"The road is passable," UDOT spokesman Adan Carillo told KSL Newsradio. He added that there is some damage to the side of the road in places, however.

Crews used snowplows to clear debris, including trees, branches and rocks, from the road, but it remained open only to emergency vehicles. Authorities predicted it reopened to general traffic early Friday afternoon.

Emergency crews became aware of the slides around 2:30 a.m. They found 10 areas of debris from about 4 miles down from Snowbird to the bottom of the canyon, between mile post 5 and mile post 8. Just before 9 a.m., Carillo said crews had cleared about 70 percent of the affected areas and were working on three remaining spots.

"Obviously, this would have been a very dangerous situation for motorists," Unified Police Department Lt. Justin Hoyal said.

UDOT speculates the slides may have been the result of a flash flood. Senior Geologist Mike Hylland with the Utah Geological Survey said it was more of a debris flood.

"The technical term for it is a hyper concentrated flood. It has to do with the percentage of sediment to water. And this appears to be a high water content," Hylland said.

When the sediment is more than 60 percent of that mixture, Hylland said it becomes a debris flow, which moves slower like wet concrete and can do more damage. In Little Cottonwood Canyon, the sediment has built up in the channels due to dry weather, and the slopes are steep. So even if the flow is not thick, the concentrated flow of water in these channels has a lot of energy and can move relatively large rocks.

UTA bus route 990 was closed Friday morning due to the slides.

Rockslides also were reported in Big Cottonwood Canyon and Millcreek Canyon but they remained open Friday morning.

Slides also occurred in Big Cottonwood and Millcreek Canyons, but travel wasn't affected there.

"Whenever you're traveling on the roads, always be aware, keep an eye out for hazards that could approach," Hoyal said.

Contributing: Jed Boal


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