CDOT to use tools to catch mudslides

“Bathtubs” and water-diversion structures aim to stop disasters

Colorado transportation officials this week said two new tools they’ll try out in Glenwood Canyon this summer may help blunt the effect of mudslides on Interstate 70 as the seasonal threat returns.

The measures amount to a series of “bathtubs” and water-diversion structures, Colorado Department of Transportation officials say. The tubs are basins that will be dug next to I-70 at high-risk spots to catch small slides before they hit the highway.

Higher up the canyon walls, CDOT says the new diversion structures and barriers should slow the flow of runoff water as gravity takes it down the watersheds — if heavy rain falls in the targeted areas, at least. A CDOT engineer said during a media briefing this week that 3,000-pound “super sacks,” akin to giant sandbags, already have proven to be an effective temporary barrier that catches falling rocks at Blue Gulch, 9News reported.

Dozens of drainage basins in the canyon were burned in the 2020 Grizzly Creek fire, which scorched more than 32,600 acres, or 51 square miles. Last summer, heavy downpours lasting as little as 15 minutes caused mudslides in multiple places, with some of them blanketing the highway in several feet of muck and rocks.

The most severe debris flows, in late July, closed I-70 for two weeks.

“CDOT has made tremendous progress in the recovery efforts from the 2021 mudflows,” CDOT executive director Shoshana Lew said in a news release Wednesday. “This includes fixing Interstate 70 in record time, removing material from the Colorado River, rockfall mitigation and numerous other tasks to get I-70 operating safely for the traveling public.”

Experts expect slide threats to last several summers, since revegetation is a slow process. CDOT says it again will prepare for safety closures in the canyon when rain is in the forecast, with full highway shutdowns during flash-flood warnings.

Slides could result in lengthy closures of I-70, triggering a long alternate route that follows Colorado 9 from Silverthorne to U.S. 40 through Steamboat Springs to Colorado 13 in Rifle.

CDOT this week provided a tally of the material trucked out the canyon to dump sites since late July’s slides: 206,355 tons.

It took months to repair one damaged section of the highway, and crews have worked through the winter to remove debris piles that landed in the Colorado River, affecting its flow. Four have been cleared near the Shoshone Power Plant, CDOT says. Work is expected to continue for the next month or so to move the remaining material in the other two piles, near Deadman Gulch (near mile marker 113) and Maneater (near mile marker 122) to improve river flow.

Also still underway is work to repair the recreation path through the canyon.

The Federal Highway Administration agreed last year to reimburse CDOT’S tens of millions of dollars in recovery and mitigation costs.