From Aspen Journalism (Heather Sackett):
Ruedi Reservoir is feeling the effects of an unusual water year, with less water for endangered fish and with low reservoir levels predicted for late summer and fall.
“This year was a strange year,” Tim Miller, a U.S. Bureau of Reclamation hydrologist who manages operations at Ruedi, said at an annual public meeting about reservoir operations held virtually Wednesday. “For most of the year, it seemed like we were doing well, we thought we would get a fill on the reservoir. However, things really turned around in late spring and early summer.”
At the meeting convened by the Bureau of Reclamation, Miller said the reservoir, which holds just over 102,000 acre-feet of water, topped out at 96,750 acre-feet this year — about 5,000 acre-feet short of filling. That means there is 5,000 acre-feet less water available this season to boost flows downstream for endangered fish in what’s known as the “15-mile reach” of the Colorado River near Grand Junction.
As reservoir levels continue to drop over the next month, Aspen Yacht Club members may not be able to access the boat ramp over Labor Day weekend. By Sept. 1, reservoir levels are predicted to be down to about 84,500 acre-feet and the surface to be at an elevation of 7,747 feet, which is 19 feet lower than when it’s full.
“After Sept. 1, it’s going to be dicey,” Miller said of accessing the private marina’s boat ramp. The U.S. Forest Service boat ramp will still be accessible at those levels, he said.
Bruce Gabow of the Aspen Yacht Club said that when water levels are 13 feet below full, the club’s docks become grounded and inoperable. He said that most years, boats are taken out of the reservoir by mid-September, but with water levels dropping sooner this year, many will need to go before the end of August.
“Everyone has kind of been expecting it, but they will be bummed out,” he said of the club’s members.
Ruedi Reservoir is currently 92% full, at 94,065 acre-feet. It topped out on July 17 at 96,914 acre-feet. In 2018, the reservoir also didn’t fill, topping out at 92,650 acre-feet, according to Miller.
Each spring, Miller must decide how much water to release from Ruedi and when to release it to make room for inflow from snowmelt. Those decisions are based on streamflow forecasts from the Colorado Basin River Forecast Center and the Natural Resources Conservation Service, as well as the Bureau of Reclamation’s statistical forecasts.
This year’s unusual conditions made for tricky forecasting, leading some to question whether more and better data collection is needed, instead of relying primarily on snow telemetry, or SNOTEL, data. These automated remote sensors collect weather and snowpack information in remote watersheds, but they provide only a snapshot of a specific location. Each of the three forecasting agencies over-predicted Ruedi inflow for the months of April, May and June.
Usually, the amount of runoff closely mirrors snowpack. And with snowpack in the Roaring Fork River basin slightly above normal, as measured by SNOTEL sites, it seemed that is where runoff would also end up. But parched soils from a dry fall sucked up some of the moisture before it made its way to streams and eventually the reservoir. Miller also suspects that a high rate of sublimation — where snow goes from a frozen state to vapor, skipping the liquid phase — may have also played a role.
“To do our statistical forecast, it’s 90% snowpack only,” Miller said. “We had some different variables this year.”
By the end of May, Miller realized inflow projections were too high and began scaling back releases. Ruedi also did not participate in Coordinated Reservoir Operations this year. In the annual CROS, which began around May 29, water managers from across the state aimed to enhance peak spring runoff by releasing water from reservoirs at the same time. The peak flows have ecological benefits, especially for fish in the 15-mile reach.
“It was pretty much a last-minute declaration we couldn’t do CROS,” Miller said.
April Long, executive director of Ruedi Water & Power Authority, suggested that water managers should explore other ways of collecting data in addition to SNOTEL information to improve forecast accuracy. The city of Aspen and Denver Water have experimented with LiDAR technology — which analyzes the reflection of laser light to create detailed three-dimensional maps — to track the depth of mountain snowpack, providing a more complete picture of the water contained in that snowpack.
“With this year of unexpected results from our snowpack and the way it melted off, I have concern that with climate change and climate variability, we are going to see more uncertainty,” Long said in a follow-up interview with Aspen Journalism. “I wonder how much benefit we could gain if we knew a little more.”
Editor’s note: This story has been updated to reflect the date Ruedi storage peaked in 2020.
Aspen Journalism is a local, investigative, nonprofit news organization that collaborates on coverage of water and rivers with The Aspen Times and other Swift Communications newspapers. This story ran in the Aug. 7 edition of The Aspen Times.