Bracing for the flood: High water expected throughout Upper Colorado River system
May 6, 2011
GRAND COUNTY – Spring flooding is likely in areas from the headwaters of the Colorado River all the way to northern Utah.
That was the message shared at this year’s “State of the River” meeting on May 4 at Mountain Parks Electric in Granby.
“Everything to Lake Powell is above 100 percent,” said Don Meyer of the Colorado River District, in an overview of May 1 forecasts for probable runoff volumes.
The Colorado Basin River Forecast Center indicates early to mid-May would be the optimum time for a prolonged warm period to melt snows and decrease the probability of spring floods.
In a series of graphs and charts, water engineers addressed area reservoirs and talked about “leaving the envelope,” or snowpack that is exceeding what has been seen since Snotel measurements began in the early 1980s.
Collectively, water engineers went out on a limb and guessed that peak runoff may take place from mid-June to the end of June, and that flows on the Colorado River at the Kremmling gauge below the confluence of the Blue River might reach around 12,000 cubic feet per second (cfs), which is about double the peak flow of last year and triple the historical average peak flow of around 4,000 cfs.
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Colorado-Big Thompson Project
For Lake Granby, Andrew Gilmore of the Bureau of Reclamation said the reservoir is expected to see 25 percent higher inflows than runoff in previous years.
With inflow forecasts on the rise since last month, the system is presently releasing water to ward off flooding downriver during peak runoff, Gilmore said.
Although runoff may compare to the record 1985 season, he said, outflows from Granby Reservoir shouldn’t reach the 3,000 cfs as they did in 1985 due to the ongoing management of the Big-Thompson system.
“This is unusual for the Reclamation as an agency,” Gilmore said. “We don’t generally do flood control. We’ll do the best that we can with the facility we have.”
That said, operators at Willow Creek Reservoir, a much smaller impoundment constructed to pump water into Lake Granby, are taking it as “low as can take the reservoir safely,” Gilmore said. That’s in preparation for projected runoff from the Willow Creek Basin, which is sitting at a record-breaking 203 percent of average snowpack.
Gilmore said Big-Thompson operators are preparing Willow Creek to capture an expected 97,000 acre-feet of runoff, or the equivalent of seven times the capacity of the reservoir.
An acre-foot would cover one acre with one foot of water.
The reservoir is expected to cap releases at about 1,100 cfs to keep “streams below the reservoir below flood flow.”
Windy Gap Reservoir will “not be pumping water this year,” said Don Carlson of Northern Water and the Municipal Subdistrict.
And Adams Tunnel on the east end of Grand Lake, which sends water to the northern Front Range for power generation and municipal and agriculture use, is running full right now, engineers said. At peak runoff, operators plan to close Adams Tunnel, allowing East Slope reservoirs to capture native runoff on the east side of the Continental Divide.
Moffat, Willams Fork
In the Moffat System operated by Denver Water, Jones Pass has tied the record for the most snow on May 1, said Bob Steger of Denver Water.
Steger said Denver Water plans to reserve a certain amount of space in Gross Reservoir to prepare for peaks on the Fraser River. But the “wild card,” he said, is Denver Water’s junior water rights on South Boulder Creek, the water from which is also stored in Gross.
At Williams Fork, Denver Water is conducting repairs on the reservoir’s outlet works, which means it is “limping on 70 to 80 cubic feet per second with temporary outlet works,” Steger said. By next week, repairs should be completed, allowing the reservoir to release more water at that time in preparation for capturing runoff.
Wolford Mountain Reservoir
Recently, Wolford Mountain Reservoir began releasing 400 cfs. Asked why reservoir operators of the Colorado River District haven’t increased releases in preparation for flooding on ranch land downstream of Wolford, Don Meyer of the Colorado River District said erosion concerns were the main reason. Also, “We don’t feel we’re going to impact any instantaneous flows into the reservoir,” he said.