Warming expected to push Yampa River above its banks next week
May 27, 2011
Cubic feet per second as measured on the Yampa River at Fifth Street
6,820 cfs: June 14, 1921
6,300 cfs: June 2, 1914
5,860 cfs: June 22, 1917
5,790 cfs: April 26, 1974
5,740 cfs: June 4, 1952
5,670 cfs: May 25, 1984
5,310 cfs: June 3, 1997
Source: U.S. Geological Survey
Steamboat Springs — A senior hydrologist with the National Oceanic and Atmospheric Administration in Salt Lake City said Friday that if forecasts of temperatures in the mid- to upper 70s come true next week, the Yampa River in Steamboat Springs is likely to reach flood stage the weekend of June 4.
"We see a big warmup as a ridge of high pressure settles over Colorado next week and we're projecting a strong chance that the Yampa there exceeds flood stage by next week," Greg Smith said. "Temperatures could be 10 degrees above average, and if that forecast verifies, we could see a lot of rivers off to the races."
Steamboat Springs weather observer Art Judson reports the average daily highs for the critical period include 69.8 degrees Wednesday and 70.1 degrees Thursday.
Mike Chamberlain, a forecaster with the National Weather Service in Grand Junction, said he foresees daily highs in the range of 75 to 77 degrees settling in by the middle of the coming week. He cautioned that the forecast could change, particularly if a southeast flow brings more clouds to Northwest Colorado than currently anticipated.
Smith said a change of 4 to 5 degrees in temperature could significantly change the rate of snowmelt.
If the river floods
The Yampa in its town stretch was flowing at a moderate 2,270 cubic feet per second Friday afternoon, pegging the average flow for this date. But the 16 feet of lingering snow on nearby Buffalo Pass means the river basin is pregnant with the possibility of a flooding river.
Flood stage isn't a place often visited in the town stretch of the Yampa based on record keeping during the past 107 years.
Aldis Strautins, a service hydrologist with the National Weather Service in Grand Junction, said it's important to note that when a river first reaches flood stage, that milestone doesn't necessarily signal widespread flooding of buildings.
"Flood stage (at the Fifth Street Bridge measuring site) is 7 feet, which would cause us to put out an advisory," Strautins said.
A measurement of 7 feet at the Fifth Street Bridge means the river is literally 7 feet above the deepest part of its channel at that point. Flood stage varies widely up and down the river depending on the width and depth of the channel. Changes in the channel and obstructions like logs wedged against bridges also make a difference, Strautins said.
"At 5 feet, where the river is now, it's likely there's some water on the bike trail at Emerald Park," Strautins said. "At 6 feet the baseball or soccer fields at Emerald might have water on them. At 7.5 feet, you'd see some flooding of properties along the river in Steamboat Springs. At 8.5 feet, the equivalent of a streamflow of 6,900 cubic feet per second, commercial buildings along Yampa Street would be impacted."
The encouraging news is that the river in downtown has never climbed to 6,900 cfs.
The two hydrologists stopped short of predicting floods on the Yampa next week, but they pointed out that the makings are in place in the mountains, depending on daily high temperatures.
"The Yampa in particular — it's just a huge snowpack," Smith said, "and it hasn't been going off."
Strautins said that given the amount of snowpack held this late into the year, it's not unreasonable to think Steamboat might set a new record for the peak flow.
NOAA's forecast for the Yampa River in Steamboat assigns a 90 percent change that the river will exceed 5,200 cfs, a 75 percent chance that it will exceed 5,500 cfs, and a 50 percent chance that it will exceed 6,000 cfs. The chances of peak flows exceeding 7,000 cfs are 25 percent, and there remains a 10 percent chance the river could exceed 8,000 cfs.
The U.S. Geological Survey and NOAA differ on the all-time peak flow in the Yampa. The latter puts it at 5,870 cfs, but the USGS shows the Yampa peaking as high as 6,820 cfs (a gauge height of just 6.64 feet) on June 14, 1921. It's almost a certainty that the channel of the river in the town stretch has changed during the intervening 90 years.
The highest peak in recent years was 5,310 cfs (7.65 feet) on June 3, 1997.
The snowpack at the Tower measuring site at 10,500 feet on Buffalo Pass actually increased at times during the week that just ended. The snow depth jumped from 178 inches on May 20 to 194 inches the next day after a 16-inch snowstorm, according to automated gauges operate by the Natural Resources Conservation Service. The snowpack there gave up 23 inches of depth due to settling and possible melting by May 25, then added a fresh 8 inches on May 26. The 79.3 inches of water stored there is 171 percent of average.
At the base of Buffalo Pass at Dry Lake Campground, the 27.8 inches of water is 772 percent of the typical 3.6 inches of water for this date. That measurement is influenced by the fact that snow at Dry Lake's 8,400-foot elevation is usually all but melted by this date.
Smith and Strautins cautioned Steamboat residents that the streams coming off Buffalo Pass, notably Soda Creek and Spring Creek, plus Walton Creek draining Rabbit Ears Pass, pose at least as much flooding danger as the Yampa. And Strautins urged people not to recreate on rivers at high water unless guided by a professional.
To reach Tom Ross, call 970-871-4205 or email tross@SteamboatToday.com
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