How low will Ruedi Reservoir go?
Bureau of Reclamation warns of potential impacts to Aspen hydro plant, water contract holders
Water levels at Ruedi Reservoir could fall so low this winter that the city of Aspen could have difficulty making hydroelectric power and those who own water in the reservoir could see shortages.
That’s according to projections by the Bureau of Reclamation, which operates the reservoir near the headwaters of the Fryingpan River. At the annual Ruedi operations meeting Thursday, officials estimated the reservoir will fall to around 55,000 acre-feet this winter, what’s known as carry-over storage. According to Tim Miller, a hydrologist with the Bureau of Reclamation who manages operations at Ruedi, the lowest-ever carry-over storage for the reservoir was just over 47,000 acre-feet in 2002, one of the driest years on record. Last year’s carry-over was about 64,000 acre-feet.
At 55,000 acre-feet, the elevation of the water is about 7,709 feet. That’s about 2 feet lower than Aspen officials would like.
“We don’t like being below 7,711,” said Robert Covington, water resources/hydroelectric supervisor for the city.
That’s because the hydro plant needs a certain amount of water pressure to operate. The higher the water elevation, the more water pressure there is.
According to Covington, power providers Xcel Energy and Holy Cross Energy sometimes temporarily and quickly shut down the hydro-electric plant when there are problems with transmission lines or they need to do repairs.
“It’s very common for these types of plants to automatically shut down,” Covington said.
The problem is that restarting the plant requires a larger amount of water than the 40 cubic feet per second that is roughly the minimum amount required to operate the plant efficiently.
“It’s very difficult for us to get back online, so we end up pushing more water through for a very short period of time,” he said.
If Aspen has to shut down the plant because flows are too low, the city could purchase more wind power to maintain its 100% renewable portfolio.
“When we go lower on hydro, we go with wind, which is generally the most cost-effective,” said Steve Hunter, utilities resource manager with the city.
Shortages to contract holders
Another consequence of low carry-over storage means that Ruedi will start out even lower next spring when the snow begins to melt and the reservoir begins to fill again. That means if there is below-average runoff again, some contract holders who own water in Ruedi could have to take shortages, something that has never happened before, Miller said.
There are 32 entities that have “contract water” in Ruedi, which the bureau releases at their request. This is water that has been sold by the bureau to recover the costs of building and operating the reservoir. The contract pool is separated into two rounds, and contract holders will take a previously agreed upon shortage amount depending on which round they are in.
“If we get another similar type of runoff this year, there will be shortages most likely to the contract pool,” Miller said.
But there are still uncertainties in predicting how low the reservoir will go. The biggest of these is how much water will be released for the benefit of the endangered fish in the 15-mile reach of the Colorado River near Grand Junction.
There is a 10,412-acre-foot pool available for the fish, but in dry years entities that store water in Ruedi will sometimes coordinate to release more fish water in the late summer and fall. This would draw down the reservoir even farther. It’s still not clear how much water will be released this fall for the four species of endangered fish.
“The release defines the carry-over,” Miller said.
Despite initial bureau forecasts in April that Ruedi could probably fill to its entire 102,373-acre-foot capacity, Ruedi ended up only about 80% full this year. July 11 was the peak fill date at 83,256 acre-feet and an elevation of 7,745 feet.
“It was probably a little over-optimistic,” Miller said of the April forecast. “But at the time our snowpack was average. It was a reasonable forecast given the conditions.”
As climate change worsens the drought in the Western U.S., Ruedi is not the only reservoir to face water levels so low that they threaten the ability to produce hydroelectric power. Last month, the bureau began emergency releases from Upper Basin reservoirs, including Blue Mesa on the Gunnison River, to prop up levels in Lake Powell and preserve the ability to produce hydropower at Glen Canyon Dam.
Aspen Journalism covers water and rivers in collaboration with The Aspen Times. For more go to http://www.aspenjournalism.org.