ASPEN — On a recent snowy morning, aquatic ecologist Bill Miller dipped what’s known as a Hess sampler into the frigid waters of Castle Creek near Aspen.
Miller stirred up the streambed with his hands, funneling the rocks, sediment and leaves — along with macro-invertebrates such as insects and worms — into the collection container.
After putting the organic material into smaller jars and giving each one a squirt of alcohol as a preservative, he ferried them to a lab in Fort Collins. Scientists there will count the number and types of bugs in each sample.
“By the different species that are there, you can get a good indication of stream and water quality, and overall ecological function,” Miller said.
Miller’s work is part of a program that will monitor the health of Castle and Maroon creeks, ensuring that Aspen Skiing Co.’s increased water use for snowmaking on Aspen Mountain won’t harm the aquatic environment of the creeks. The stream-monitoring program was set out in September as a condition of Pitkin County’s approval of Skico’s Aspen Mountain Ski Area Master Plan.
“I think the idea of this is we don’t want the snowmaking to cause significant harm to the creeks,” said Andre Wille, chairman of Pitkin County Healthy Rivers board.
Aspen Mountain expansion
As part of its planned expansion, Aspen Mountain will use an additional 57 acre-feet of water per season, bringing the total average snowmaking water use to roughly 257 acre-feet. For context, Wildcat Reservoir, which is visible from the Snowmass Ski Area, holds about 1,100 acre-feet of water.
Skico is expanding its snowmaking for the 2020-21 season on 53 acres near the summit of Aspen Mountain, which will make it easier to have reliable and consistent snow coverage to ensure a Thanksgiving opening. Skico draws its water for snowmaking on Aspen Mountain from the city’s treated municipal supply, which is from Castle and Maroon creeks.
When Skico makes snow in November and December, the upside is there are fewer municipal water users pulling from local streams — outdoor irrigation season is over and holiday crowds have yet to arrive —but snowmaking uses water when natural streamflows are at some of their lowest points of the year.
“We were definitely concerned with the possibility of too much water being taken out in those early months of the winter,” Wille said.
Miller collected samples from above and below the city’s diversion dams on both lower Castle and Maroon creeks. His samples will act as a baseline against which the condition of the streams in future — and perhaps drier — years will be measured.
According to the resolution approving Aspen Mountain’s master plan, if the county’s aquatic ecologist determines, in future years, that the additional water usage is having a negative effect on stream health, the county could limit Skico’s water use to historical levels — about 200 acre-feet a year.
There is another safeguard to keep water in the river, but some say it may not go far enough to ensure stream health.
The Colorado Water Conservation Board, a state agency, holds instream-flow water rights on both Castle and Maroon creeks. And the state has determined that it requires at least 12 cubic feet per second of flowing water to protect the environment to “a reasonable degree” on lower Castle Creek and 14 cfs on lower Maroon Creek.
“We don’t feel it’s advisable to look at what the CWCB may have decreed in the past for a minimum instream flow,” said John Ely, Pitkin County attorney. “That’s not necessarily indicative from a scientific point of view of what is actually needed to maintain a healthy stream.”
That’s why the county hired Miller — who also is the longtime consulting biologist for the city of Aspen — to do its own assessment of stream health.
Ely said stream samples may not need to be taken every year — just in dry years when snowmaking could exacerbate already low flows. He estimated the annual cost of the monitoring program at about $5,000 to $10,000.
Jeff Hanle, Skico’s vice president of communications, said the company is taking steps to increase the efficiency of its on-mountain storage for snowmaking, such as adding two new ponds on Gent’s Ridge, so it won’t need to pull as much water from the city’s supply during the early season.
Although Skico and Pitkin County still need to work out the details of the stream-monitoring program, Hanle said the company is on board with preserving the ecological health of Castle and Maroon creeks.
“We would not make snow if it’s harming the stream, even if it could shorten a season,” he said. “We aren’t going to damage our home.”
Aspen Journalism collaborates with The Aspen Times and other Swift Communications newspapers on coverage of rivers and water. This story ran in the Nov. 11 edition of The Aspen Times.