Mudslide warning system proposed for Aspen Mtn.
At least one city official would like Aspen to have a little forewarning, should a big chunk of Aspen Mountain be inching closer to breaking free and flowing into town in a giant mudslide.
City engineer Nick Adeh said he will propose that several entities, including the city, Pitkin County and the Aspen Skiing Co., share in the cost of an early-detection system.
His comments came during a half-day discussion Tuesday on the city’s drainage master plan and a proposal to upgrade Aspen’s storm-sewer system with a $5 million project.
Speakers included representatives of the Federal Emergency Management Agency, local officials, a U.S. Geological Survey representative and Alan Leak, the consultant who has helped the city prepare its drainage plan.
The program began with a short news video about a 1997 mudslide at an Australian ski resort that buried 19 people and crushed two lodges.
“This is something that can happen in our community,” Adeh said. “I’m not saying that it will, but geologic hazards do exist in our community.”
Small events already occur, Adeh noted, showing a slide of the 1997 mudslide in Keno Gulch on the western flank of Aspen Mountain. It buried several vehicles and damaged the Aspen Music School campus along Castle Creek.
And mudflows along Ute Avenue and other areas near the base of the mountain are a regular occurrence during heavy downpours when the ground is already saturated, Adeh pointed out.
The city’s engineering department, working with consultant Leak of WRC Inc., has come up with a $5 million, four-year project to upgrade the city’s storm-drainage system so it can handle a “10-year flood event.” It will be presented to the Assets Management Committee, which advises the City Council on fiscal matters, at the end of the month.
The city’s existing storm system varies in capacity around town, Leak noted. It could could contain perhaps a 2- to 5-year event, he said. “If you get a more significant event, you’re going to have a great deal of material flowing overland,” he said.
And a 100-year event could bring chest-deep mud pouring into parts of town from the slopes of Aspen Mountain, according to Leak’s analysis.
“There are real risks that people could get seriously hurt or killed if this event occurred,” he said.
Leak’s consulting firm, which has worked in various flood-hazard areas around Colorado and the West, has put together a set of drawings and illustrations that indicate three potential routes for a massive mudslide down the face of Aspen Mountain. These three routes follow Pioneer, Vallejo and Spar gulches, which converge at the base of the mountain.
According to computer models, a sudden downpour of rain on top of leftover snow and saturated ground in the springtime could trigger a massive movement of mud streaming down the gulches and into town.
The proposed upgrade to the storm sewer system would not handle such an event. More likely, such a mudslide would trigger a disaster response, said Darryl Grob, Aspen fire chief.
“An event like this would generate a tremendous number of victims,” he said.
“The slopes are very steep,” added Adeh. “The reaction times are very short. We would not have time to evacuate the town.”
The early-warning system, being used in places like California, where landslides are common, would cost about $200,000. The sensitive equipment would be placed at nine separate points to detect a shift in the soils, according to Adeh.
Other options explored during Leak’s study include placing structures on Aspen Mountain to halt a serious mudflow. Boulder-lined channels with pipe underneath to take water off the mountain could cost $15 million to $20 million, Leak said.
One hundred buried cutoff walls made of concrete to prevent sediment from moving is a less costly option, at about $15 million. But Leak said the effectiveness of such an approach is difficult to determine.
Making changes on Aspen Mountain, which is outside the city’s jurisdiction, would require the cooperation of the county and the Skico, officials noted.
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