- Associated Press - Saturday, May 2, 2015

COLLBRAN, Colo. (AP) - The future remains uncertain for the site of last year’s West Salt Creek Landslide. But experts monitoring the slide assure Collbran area residents that they remain vigilant and plans are in place should something go awry.

About 50 people attended a two-hour community meeting recently to get an update on the slide. Jeff Coe, a geologist with the U.S. Geological Survey, said a pond that has formed near the top of the slide above a giant block of debris is gaining water, but not much is happening on the rest of the slide site.

Coe said it’s difficult to say how likely it is the pond will overflow and potentially send debris tumbling downhill. But if that happens, he said, the most likely scenario is that debris will spread to just a 1-million-cubic-meter (yard) area near the top of the 30 cubic-meter slide site. A less likely scenario is that debris will spread from the pond to the end of the current slide site. Even less likely, Coe said, is that debris will crawl beyond the end of the slide, encompassing an area of about 65 million cubic meters.

The pond isn’t likely to overflow any time soon, according to Ben Stratton, a hydrologist with Grand Mesa, Uncompahgre and Gunnison National Forests. If it did, Stratton said there is plenty of bumpy terrain and some existing pond-like divots for water spilling out of the pond to fill on the way down the slide

The pond is about 60 percent full with 240 acre-feet of water. Officials say one acre-foot is enough to serve two families for a year.

The pond is filling at an average of six-tenths of an acre-foot per day, Stratton said. Even if it filled at the maximum rate recorded so far of 3 acre feet in a day, the pond would have to consistently fill at that rate for nearly eight weeks to reach capacity. “It’s sort of looking unlikely we’ll fill the pond this year,” Stratton said.

Mesa County Emergency Manager Andy Martsolf told the audience a U.S. Army Corps of Engineers study predicted that a pond spill of mostly water, not debris, would take anywhere from two hours and 55 minutes for a spill of 300 acre-feet of water to five hours and 35 minutes for a spill of 500 acre-feet of water to go down the slide, into West Salt Creek and reach Plateau Creek above Collbran. Those estimates grow to three hours and 10 minutes and five hours and 55 minutes, respectively, to reach the portion of Plateau Creek below Collbran.

In the event of a debris or water event that could threaten homes or lives, Don Hendricks with the Mesa County Sheriff’s Office said residents should evacuate the town, potentially to staging areas. Martsolf said residents would receive a reverse 911 call and be asked to evacuate only if a life-threatening event seems imminent. If instead there are just slight changes to the slide site, experts will increase monitoring and make more site visits to the area and residents won’t likely hear much about it. They may receive a reverse 911 call or see equipment moved to the site if changes to the slide area accelerate but not to the point of imminent flooding.

Coe said this continues to be a time to monitor the slide area, pay attention to any changes and prepare for any scenario.

“We need to be aware from a community point of view and our point of point of view and be prepared to act,” he said.


Information from: The Daily Sentinel, https://www.gjsentinel.com

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