From Aspen Journalism (Brent Gardner-Smith):
As my raft floated under the railroad bridge at the confluence of the Roaring Fork and Colorado rivers last week, I was wondering just how much water would flow out of the Fork and into the Colorado this year.
Certainly less than average, given that the snowpack peaked in March and began melting off, I mused, taking a stroke to catch the big eddy that forms just shy of the mighty Colorado, where the Fork comes in across from Two Rivers Park in Glenwood Springs after draining 1,543 square miles of land.
Perhaps the wet and cold weather of late April and much of May will continue to forestall a sudden flash of melting snow, so what snow we still have in the high country will come off in a nice steady fashion.
But spinning around the eddy, I knew how easy it was, as a boater, to be wrong about water and weather. It is also, as it turns out, a tricky time of year for professional hydrologists to predict run-off, as data from low-elevation snow-measuring sites tapers off and daily weather conditions can play a big role in shaping how much water flows, and when it does.
In mid-March, which felt like summer already, a trip on the Green River starting April 12 seemed like a good bet this year to enjoy some warm weather. But a big storm swept in that week and blasted the river with freezing rain.
The same storm laid down 11 inches of snow on Aspen Mountain by Friday, April 17, making for a memorable closing weekend for some.
After warming up from that trip, I ventured optimistically out again during the first full week of May, this time on the Colorado River west of Loma. And I was soon engulfed in the downpours of May 5 and 6 that lead to river levels across the region jumping up.
Between May 5 and May 7, for example, the flow in the lower Fork doubled from a 1,000 cubic feet per second to over 2,000 cfs.
So when I went out on May 13 for my first trip of the season down the Roaring Fork from Carbondale to Glenwood, I wasn’t surprised that it started raining. It’s just been that kind of season so far — in fact, through May 19, total precipitation in the Roaring Fork River watershed was 204 percent, or double the normal amount of precipitation. according to the Natural Resource Conservation Service (NRCS).
But the Fork was flowing that day at 1,110 cubic feet per second, which was enough water to have a perfectly nice float, especially as I did see some sun (and some red-wing blackbirds).
But will the river get much bigger this year, I wondered as I rowed toward Glenwood.
Below average flows
The Colorado River Basin Forecast Center in Salt Lake City forecast on May 19 that the Roaring Fork will most likely peak this year in mid- to late June at 4,300 cfs, as measured at Veltus Park, just above the Fork’s confluence with the Colorado.
That’s 73 percent of the Fork’s average annual peak of 5,920 cfs, which typically occurs between May 29 and June 23.
While this year’s likely peak flow of 4,300 cfs is certainly better than the lowest peak flow on record — 1,870 cfs on June 3, 2012 — it’s also way below the historic peak of 11,800 cfs on July 13 in 1995.
The forecast peak flow has increased given the cool and wet weather in May. So, if April showers bring May flowers, May showers are likely to bring better boating on the Fork in June.
“I would say it is very likely (the Roaring Fork) will see a below average peak flow this year,” said Brenda Alcorn, a senior hydrologist with the Forecast Center.
However, she added that what snowpack we do have “is in better shape than it was in 2002 and 2012, so I do not expect a record low peak.”
But just how much water comes, and when, is now weather dependent.
“Spring temperatures and precipitation play a significant role in the pattern of snowmelt runoff and consequently the magnitude of peak flows,” Alcorn said. “An extended period of much above normal temperatures or heavy rainfall during the melt period can cause higher than expected peaks, while cool weather can cause lower than expected peaks.”
On Friday, May 15, Julie Malingowsky, a meteorologist with the National Weather Service in Grand Junction, said the period to at least May 25 looked cooler and wetter than normal, and longer-range forecasts indicate that the next several months could be wetter than normal.
(Also, see the Intermountain West Climate Dashboard of indicators at Western Water Assessment)
But probably not wet enough make up for the skinny snowpack.
“Even though it has been a wet month, we are still drier than normal,” Malingowsky said.
Below average supply
Another view of this year’s water picture is available from the Natural Resources Conservation Service’s “Colorado Water Supply Outlook Report,” which was published on May 1.
The report shows that the “most likely” amount of water to reach the bottom of the Roaring Fork between April and the end of July is 450,000 acre-feet, according to Brian Domonkos, a data collection officer with NRCS.
That’s below the 30-year average of 690,000 acre-feet flowing down the Fork for the period from April to August. (The Roaring Fork delivers, on average, 871,100 acre-feet of water to the Colorado River over a full year, according to the Colorado Division of Water Resources).
The water-supply report said that current conditions point to “a below normal streamflow forecast picture for much of the state heading into spring and summer of 2015.”
However, Gus Goodbody, a forecast hydrologist with NRCS, said the amount of water expected to flow out of the Roaring Fork is likely to increase from the May 1 forecast by five to 10 percent, given May’s weather so far.
“It’s going to go up,” he said.
Another indicator of potential run-off is the measure of the “snow water equivalent” at SNOTEL measuring sites in the Roaring Fork basin.
The average from the eight SNOTEL sites in the Roaring Fork basin was 108 percent on May 19, but that’s without complete data from four of the sites.
That number — 108 percent — has been climbing steadily since May 1, but it’s not an indicator that the snowpack has been growing. What it does show is that the cool and wet weather has slowed the run-off and moved the data closer to the historic average — which, again, bodes well for June boating. But in addition to the snowpack and the weather, there are other factors that dictate the flows in the Fork at Glenwood Springs.
Off the top
An average of 40,600 acre-feet of water a year is collected from the upper Roaring Fork River basin and sent through a tunnel under Independence Pass and into Twin Lakes Reservoir, destined for Aurora, Colorado Springs, Pueblo and Pueblo West.
The Twin Lakes diversion takes 40 percent of the water out of the upper Roaring Fork basin above Aspen, according to the 2012 Roaring Fork Watershed Plan.
Another 61,500 acre-feet is collected on average each year from tributaries of the upper Fryingpan River and sent east through the Bousted and Busk tunnels. That accounts for 37 percent of the water in the upper Fryingpan headwaters.
As such, there are many days when there are rivers heading both east and west out of the Roaring Fork River watershed, and the ones heading east can often be bigger.
For example, on May 13, while I was floating on 1,110 cfs at the bottom of the Fork, there was 136 cfs of water running under the Continental Divide in the Twin Lakes — Independence Pass Tunnel, which can, and does, divert up to 625 cfs later in the runoff season.
And the Bousted Tunnel, which transports the water collected from the headwaters of the Fryingpan River, as well as Hunter and Midway creeks in the Roaring Fork basin, was diverting 101 cfs on May 13.
Meanwhile, the gauge on Stillwater Drive on May 14 showed the main stem of the Fork was flowing, just east of Aspen, at 111 cfs.
Then there is the water diverted out of the rivers in the basin and into one of the many irrigation ditches along the Fork, the Crystal and other streams in the basin.
Ken Ransford, a member of the Colorado River Basin Roundtable, estimates that the 12 biggest irrigation ditches on the Roaring Fork and Crystal rivers divert about 115,000 acre-feet of water a year.
Most of that water eventually finds its way back to the rivers, but the diversions also leave many stream reaches lower than they otherwise would be, and few tributaries are left untouched.
According to the Roaring Fork Watershed Plan, “flow-altered stream reaches include the Roaring Fork, Fryingpan, and Crystal rivers, as well as Hunter, Lincoln, Maroon, Castle, West Willow, Woody, Snowmass, Capitol, Collins, Sopris, Nettie, Thompson, Cattle, Fourmile, and Threemile creeks.”
Another factor shaping the flows in the lower Fork are decisions made by regional water managers, including irrigators near Grand Junction and municipal water providers in Denver, that can shape releases from reservoirs such as Green Mountain and Ruedi.
Who needs water, and when, can also dictate the size of that eddy at the bottom of the Fork. So for now, I’m just glad it’s big enough to float a boat.
Editor’s note: Aspen Journalism is collaborating with The Aspen Times, the Aspen Times Weekly, and The Glenwood Springs Post Independent on coverage of rivers and water. The Aspen Times Weekly published this story on Thursday, May 21, 2015.
More Roaring Fork River watershed coverage here.