CU Boulder researchers harness 35 years of data to uncover responses of a high-elevation reservoir to a warming world
The surface waters of Lake Dillon, a mountain reservoir that supplies water to the the Denver area, have warmed by nearly 5 degrees Fahrenheit (2.5 degrees Celsius) in the last 35 years, which is twice the average warming rate for global lakes. Yet surprisingly, Dillon does not show adverse environmental changes, such as nuisance algal blooms, often associated with warming of lakes. Researchers at the CIRES Center for Limnology, who have just published a multi-decadal study of Lake Dillon, conclude that the lake’s rapid warming and its lack of ecological response to warming are explained by the high elevation of the lake.
“The warming of Lake Dillon is a result of climate change but, in contrast with warm lakes, which respond in undesirable ways to warming, Lake Dillon shows no environmental response to warming, said William Lewis, Director of the CIRES Center for Limnology and lead author of the new paper published today in AGU’s Water Resources Research. “The explanation for the lake’s ecological stability lies in its low temperature, which serves as a buffer against ecological effects of warming.”
Since 1981, Lewis and colleagues in the CIRES Center for Limnology have collected detailed information not only on Lake Dillon’s temperature, but also on its water quality and aquatic life. Full vertical profiles of water temperature document changes in vertical distribution of heat over time. The record shows that warming of tributary water contributes to warming of the lake’s deepest waters.
“The 35-year data set allows us to see the complete warming pattern of the lake,” said James McCutchan, associate director of the Center. Natural events, including droughts and floods, create interannual variation that obscures the effects of climate change over short intervals, whereas multidecadal data sets can show more clearly the effects of climatic warming.
Dillon is the highest lake yet studied for full water column warming, as Lewis and his colleagues note in their paper. The study also is the first to analyze warming in a reservoir, rather than a natural lake.
“Reservoirs can differ fundamentally from other lakes in their response to warming because they often release water from the bottom as well as the top of the water column,” said Lewis. “They can warm not only from the top, in response to solar radiation reaching the surface, but also from the bottom, as tributaries subject to climatic warming replace cold bottom water with progressively warmer tributary water.”
The Lake Dillon study program is sponsored by Denver Water, which uses the water for treatment and delivery to Denver residents, and by the Summit Water Quality Committee, which represents the interests of local residents in preservation of Lake Dillon’s water quality.
Colorado water managers are saying good riddance to water year 2018. It enters the history books alongside 2002 and 1977 as one of the driest on record for the Upper Colorado River Basin.
According to preliminary numbers from the Bureau of Reclamation, water year 2018, which ended Sept. 30, had the third-lowest unregulated inflow into Lake Powell at 4.62 million acre-feet. That’s just 43 percent of average.
Only 1977 and 2002 saw less water flow into Lake Powell from the upper basin, at 3.53 million acre-feet and 2.64 million acre-feet, respectively.
The average yearly inflow is 10.8 million acre-feet.
The months of August and September 2018 were the third- and fourth-worst months for unregulated inflows into Lake Powell behind only July and August of 2002.
The unregulated flow in August was just 2 percent of average. Lake Powell is currently 46 percent full.
“We know if we have another drought, the risk of draining Lake Powell is real,” said Jim Pokrandt, director of community affairs for the Colorado River Water Conservation District and chairman of the Colorado Basin Roundtable. “If we have another year as bad as this one, you’re going to see lots of discussions about who’s going to take reductions. We really need three, four, several years of average or above-average snow years to get us out of this pickle.”
Roaring Fork conditions
Locally, the Roaring Fork watershed was extremely dry this water year. The region was plagued by record-low snowpack — the lowest snow-water equivalent ever recorded for some dates at the McClure Pass and Independence Pass SNOTEL sites — sparse runoff, record-low streamflows and a hot, dry summer.
Low flows were prevalent across Colorado during the last two weeks of the water year, which runs from October through September. According to the National Oceanic and Atmospheric Administration’s drought information system, 30 percent of U.S. Geological Survey stream gauges in the intermountain West reported record-low seven-day-average stream flows for the last two weeks of September, including some in the Roaring Fork watershed.
On Sunday, the last day of the water year, the USGS river gauge on the Roaring Fork at Stillwater Road just east of Aspen showed the river flowing at 19 cubic feet per second, beating the previous minimum flow of 21 cfs in 1977.
Flows on the Crystal River were similarly low. Above Avalanche Creek and above a series of diversion structures, the river was running at nearly 46 cfs, lower than the previous record low of 48 cfs in 1977.
At the river gauge near the state fish hatchery and downstream from several diversion structures just outside of Carbondale, flows dribbled down at just under 7 cfs Sunday.
Colorado Department of Water Resources Engineer for Division 5 Alan Martellaro said the summer’s weak monsoons exacerbated conditions caused by little snowfall.
“We had a bad snowpack,” Martellaro said. “It was not the worst, but then we have had an incredibly dry summer, a total lack of rain. I think when we start analyzing it, we are going to find the flows in late summer are unprecedented. We have done some things we have never done before.”
Martellaro is referring to curtailment on the lower Crystal in late July. Amid rapidly dropping flows, the district 38 water commissioner turned down the headgate of the Lowline Ditch, which he determined was diverting too much water. The ditch diversion did not exceed its legally decreed amount; the problem was that it was violating new state guidelines regarding wasting water.
According to data from the Natural Resources Conservation Service, many sites around western Colorado rank as the driest since recording began for water-year precipitation, including McClure Pass, Schofield Pass and Independence Pass.
Statewide, the water year precipitation average at all SNOTEL sites measured just 21.4 inches, which is 64 percent of average — the second-lowest on record behind only 2002.
“It was pretty consistently dry throughout the entire year,” said Karl Wetlaufer, a hydrologist with the NRCS Colorado Snow Survey. “February may have been the only month where we had near-normal precipitation across the state.”
In some instances, reservoir releases have come to the rescue of downstream anglers, fish and ecosystems.
Releases from Ruedi Reservoir will continue through October to bolster flows for endangered fish in what’s known as the 15-mile reach, a notoriously dry section of the Colorado River between the Palisade area and the confluence with the Gunnison River in Grand Junction.
[Reclamation has been releasing water from] Ruedi Reservoir.
Periodic releases from Green Mountain Reservoir near Kremmling also boosted summer flows in the Colorado River. But that water will need to be replaced this winter by snowfall, Martellaro said. Ruedi Reservoir is currently 63 percent full while Green Mountain Reservoir is nearly 46 percent full.
“Where we have large reservoirs that can supplement the flows, yeah, we’ve gotten by,” Martellaro said. “But even that is coming to an end. We are running out. It remains to be seen what the snowpack is like to refill these large holes we’ve put in these reservoirs.”
This evening, 17 September, 2018, we at Reclamation adjusted releases from Green Mountain Reservoir to the Blue River from 525 to 475 cubic feet per second (cfs). Releases will remain at 475 cfs until further notice.
Feel free to contact me with any questions at firstname.lastname@example.org or by phone at 970-962-4326.
Staff at Frisco Bay Marina are trying to keep up with water levels that are dropping about one inch per day.
“And so an inch a day going down means the water line is moving 10 feet out every day, so we have to keep chasing it and moving the docks, which is definitely a lot of work,” said Tom Hogeman, the marina’s general manager…
Hogeman said he hasn’t seen the water this low since 2012 and it will only continue to go down as we head into the fall. The marina is typically open for rentals through mid-October but this year the season could end early.
FromThe Grand Junction Daily Sentinel (Dennis Webb):
The Colorado River District has agreed to boost water levels to help fish in the Roaring Fork River watershed while also conserving water for use by local irrigators later in the season and improving the chances for boosting flows this fall for endangered fish.
The action also could help protect water quality in the case of anticipated ash in waterways due to expected flooding and debris flows resulting from the Lake Christine Fire near Basalt.
The river district is releasing water from Ruedi Reservoir above Basalt to boost flows in the Fryingpan River and Roaring Fork River to help reduce water temperatures to benefit trout. Low flows and warm temperatures in western Colorado have led to Colorado Parks and Wildlife urging anglers to avoid fishing later in the day on numerous western Colorado waterways due to the stress trout currently are facing.
The U.S. Bureau of Reclamation approved the river district releases last week. They are expected to range between 50 and 100 cubic feet per second.
River district spokesman Zane Kessler said the water to be released is owned and managed by the river district’s enterprise…
The water technically is being delivered downstream for Grand Valley irrigation needs but is creating environmental benefits on its way there. The water otherwise would have been delivered from Green Mountain Reservoir south of Kremmling.
Kessler said the Ruedi releases will allow for conserving a part of what’s called the historic users pool at Green Mountain Reservoir for use later in the season, which would benefit Grand Valley irrigators. The releases also increase the chances that, despite it being a dry year, that pool can be declared to have a surplus. That surplus could then be delivered in September and October to what’s known as the 15-Mile Reach, a stretch of the Colorado River in the Grand Valley where the flows would benefit endangered fish.
“This has never been done before,” Kessler said of the flow agreement. “But we’ve rarely seen river levels like this before either.”
The potential for easing the impacts of ash flow also could be felt in the Grand Valley. There is concern that ash flows could force the Clifton Water District to suspend use of Colorado River water. Area water providers have an agreement to help each other in meeting short-term water needs should that kind of emergency situation arise, but doing so this year would further deplete drought-stressed supplies.
Kessler said retaining some Green Mountain Reservoir water for release later in the year also could benefit recreational uses of the Upper Colorado River.
Meanwhile, the river district is taking another step aimed at helping ensure that benefiting fish in the Roaring Fork Valley doesn’t harm fish on the Colorado River upstream of the Roaring Fork confluence. The district is currently delivering what Kessler called “fish water” from Wolford Reservoir north of Kremmling into the upper Colorado River because it is having to lower the reservoir’s water level in preparation for doing some work on the dam there.
In that book, working with John Fleck of Albuquerque, he’s trying to make the case that science should not be ignored in figuring out how to manage the Colorado River during the 21st century—as it was when Congress approved the 1922 compact governing allocations among the seven states, Indian tribes, and, somewhat more fuzzily, Mexico.
Kuhn was honored recently in Glenwood Springs by his staff and others from around Colorado for his 37 years of work.
Trained as an electrical engineer, Kuhn had been a naval office on a nuclear-powered submarine before pursuing a career in nuclear power plants. But even in 1981, he could see that nuclear power wasn’t going in the right direction. When he noticed an advertisement in the Wall Street Journal for a position at the Glenwood Springs-based water district, he applied.
Obviously, he got the job, moving from energy to water, from California to Colorado.
It was sharp pivot in Kuhn’s life. And Colorado since 1981 has also pivoted hard in very fundamental ways in its conversations about water.
Tom Alvey, who grows fruit and operates a packing shed in Hotchkiss, credited Kuhn with providing transparency and “getting the facts right” during his time as general manager of the Colorado River Water Conservation District, beginning in 1996.
Bill Trampe, who owns a ranch that sprawls between Crested Butte and Gunnison, lauded Kuhn for having “the foresight to see where we were headed and what we needed to do to be effective in protecting water for the Western Slope.”
Peter Fleming, the river district’s general counsel, testified to Kuhn’s “highly intellectual approach to negotiations.” As arguments and counterarguments were waged at one session, said Fleming, he observed Kuhn scribbling into a notepad. Peering over his boss’s shoulder, he said, he saw numbers. What did they represent? “He was calculating complex integers,” Fleming discovered. In that scribbling could be seen a larger lesson.
“He wasn’t disinterested in what was going on,” said Fleming. “He just knew that the timing wasn’t right for him to offer what would inevitably be a good solution.”
Denver Water’s Jim Lochhead was also at the gathering in Glenwood, just a few blocks from where he had for many years staffed the “Aspen office” of one of the state’s leading law firms. Lochhead drew attention to Kuhn’s influence beyond Colorado’s traditional Eastern Slope versus Western Slope schisms to the broader seven-state Colorado River Basin. There, Kuhn’s voice about preparing for a warming climate has become influential.
“He is collaborative. He is innovative. He thinks about different solutions. He listens. He tries to find the common ground,” said Lochhead, now chief executive of Denver Water, an agency that provides water to 25 percent of all Colorado residents.
A time of pivots
Nobody, however, spoke directly to the giant pivots in water politics, policies and problems in the 37 years since Kuhn arrived in Colorado.
One of the largest pivots had already begun in 1981. The federal government had spent most of the 20th century building the giant dams, canals and other hydraulic infrastructure in the West. In Colorado, the greatest ambition was evident in the gigantic transfer of water from the Colorado River headwaters near Grand Lake to the benefit of farmers in northeastern Colorado. It’s called the Colorado-Big Thompson Project.
The transfer—some would call it a heist — was opposed on the Western Slope, of course. One result of the compromise was a 1937 state law that created the river district and charged it with “conservation, use and development of water in the Colorado River and its principal tributaries in Colorado.” It covers 15 counties, including Pitkin, Garfield and Eagle. Southwestern Colorado has a similar district.
Another outcome was federal construction of Green Mountain Reservoir, on the Blue River north of Silverthorne. The dam had immediate benefits to the Western Slope, helping regulate flows to the benefit of farmers around Grand Junction. Much later, the regulated flows were crucial to providing water for endangered fish species in the Colorado River.
A later enterprise, the Fryingpan-Arkansas Project, hewed to the same template: It diverts water from the Roaring Fork drainage to farmers in southeast Colorado. For this, the Western Slope got Ruedi Reservoir. It was completed 50 years ago.
More projects were proposed, but in 1977 President Jimmy Carter announced they wouldn’t get funded. Westerners bristled and ridiculed Carter as a peanut-farmer in rain-drenched Georgia who didn’t understand the West. Ronald Reagan, arriving at the White House in 1981, was heralded as a Westerner who would right things. He only went half-way: Locals would have to come up with half the money for their dams and diversions. For most projects, it wasn’t nearly enough.
Kuhn noted that during his time, two of the five projects on Carter’s hit list in Colorado were eventually built, if not to the sizes originally envisioned. One of them, Ridgway Reservoir (originally called Dallas Divide), provides hydroelectricity that is part of Aspen Electric’s 100 percent renewable portfolio.
Altogether, however, the river district during Kuhn’s time had a hand in building five smaller-size reservoirs. Wolford Mountain Reservoir near Kremmling, by far the largest, is two-thirds the size of Ruedi. It was built in co-operation with Denver Water.
The River District under Kuhn also worked with Denver Water on other projects. But when Kuhn started work in Glenwood Springs, the relations were rocky. Denver wanted to build a giant dam in the foothills southwest of the city. Two-thirds of the water behind the Two Forks Dam was to have come from the Western Slope, primarily Summit County. Water was to go to Denver’s fast-growing suburbs.
Kuhn had been assigned to represent the river district on a task force appointed by then-Gov. Dick Lamm, to help sort through the controversy. The Western Slope task force aligned with the environmental community and together they conceded need for a small Two Forks as well as expanded diversions from Winter Park area for an enlarged Gross Reservoir west of Boulder. In exchange, the task force said, Denver needed to commit to greater water conservation. Denver Water’s leaders, confident of their rightness to the point of cockiness, refused.
The drama was cut short in 1991 when the administration of President George H.W. Bush vetoed the project, which was to be on federal land, based on environmental impacts.
Kuhn points out that the levels of conservation the Western Slope and environmentalists asked of Denver were much less than what has actually occurred. Denver Water now uses the same water for roughly double the number of people it did in 1990. The default expectation of ever-more water supplies has been shattered.
“You have this decoupling of municipal growth and water use, and we really didn’t see that coming in the early 1980s,” Kuhn said in an interview last week.
Denver, Aspen and other communities have been part of a national trend of declining per-capita use of water that may be far from over. It’s a simple matter of economics. Wringing the sponge of water conservation is cheaper. More expensive is buying water from farms on the Great Plains, but it’s still cheaper than developing new supplies.
Still being debated is how much water Colorado has to develop out of its entitlement, under compacts governing the Colorado River. As with Two Forks, a notion that the solution to water shortages is to build more dams and divert more still lingers. It assumes water remains available. A state report issued several years ago concluded that Colorado had as much as 1.5 million acre-feet of water in the Colorado River to develop.
Kuhn scoffed at that estimate. He said then that no more than 150,000 acre-feet remained—and, quite possibly, not even that. Even allocations for existing water uses are questionable because of the dangling uncertainty of the warming climate.
After rummaging around climate change science beginning in about 2000, Kuhn became increasingly vocal through published papers and other work about the need to recognize the profound implications of a warming climate on water supplies in the Colorado River and the demands.
“I was just reading some of the work that was coming out in the early 2000s, and it’s largely proven to be generally correct,” he said last week. “I am surprised how quickly it has come on, because there is so much noise in the system,” he added, referring to the inherent variability of weather, both temperature and precipitation. “Even from one year to the next there can be a lot of noise.”
A cloudy crystal ball
What this means exactly for Colorado is still hard to say. There’s still too much uncertainty about impacts to justify significant infrastructure investments at this time, according to even Denver Water. Kuhn agrees.
“It will take a long time to see how that pattern (of change) sets up,” he said.
Climate modeling suggests—but with low confidence—less snow and precipitation for southern Colorado and more for northern Colorado. The Elk Range between Aspen and Crested butte can be seen as a divide between that wetter and drier future.
“If I were in the southwest, in Durango, I would be a heck of a lot more concerned than if I were in Steamboat Springs, based on what we know now—but it’s still a guess,” he said.
For the broader Colorado River Basin, though, Kuhn expects less water in the Colorado River as it flows into the Grand Canyon past Lees Ferry. In this, last winter was a harbinger of the future. There are profound implications for how the seven states of the Colorado River Basin – plus Mexico—move forward.
And that is the big idea for the book now being written. In it, he and Fleck point to a report issued before the Colorado River Compact was formally adopted by Congress in 1928. The framers of the compact had assumed 16.4 million acre-feet average flows in allocating the waters among the seven basin states — with more yet due Mexico. In fact, flows during 20th century proved to be somewhat less, about 15 million acre-feet. The report provided accurate evidence of lesser flows beginning in 1875 and, more circumstantially, to 1850.
In other words, it was wishful thinking to assume so much water — and based on what is known about global warming, it’s fair to assume even less water in the 21st century. Through the first 14 years of the century, according to the research of Brad Udall and Jonathan Overpeck, flows have declined 19 percent.
“It’s a story about ignoring inconvenient science,” Kuhn said of the book. “If you had accepted the science, it would have made the political job [of apportioning the waters] much more difficult.”
It’s a story from a century ago, he said — but one fully relevant going forward.