Dam releases to Blue River slow
Summit Daily News
Slightly lower temperatures Wednesday and Thursday have slowed spring runoff slightly in Summit County, prompting managers of Dillon Reservoir to reduce outflows from the dam.
Denver Water’s Bob Steger said inflow forecasts from the Colorado Basin River Forecast Center have dropped since last week from between 185,000 and 219,000 acre-feet during the June 1-July 15 period to between 180,000 and 198,000 acre-feet. Still, tributary creeks and streams are swollen with water.
“Because of the reduced inflow forecasts, we need to reduce the outflow to assure that the reservoir fills,” Steger said. “We are currently in the process of reducing the outflow from 1,300 cubic feet per second to 1,100 cfs.”
The dam provides some protection from flooding for residents downstream of the reservoir along the Blue River, Silverthorne public works director Bill Linfield said.
“You don’t see widespread flooding here even when we go over 1,800 cfs,” he said, adding he’s been in the area since 1976 and only once did he see the river run between 1,900 and 2,000 cfs, which is considered an action stage (a nuisance, not widespread flooding) by the National Weather Service. Areas at risk at the action stage are the Willow Grove neighborhood and homes across the river from the development. The Blue River has been running at about 1,300 cfs.
“Going over 1,800 cfs isn’t necessarily a catastrophic event for the town,” Linfield said, “but you do get some areas that see localized flooding.”
Such as the South 40 subdivision by Silverthorne Elementary, which was affected with standing water when the river reached 1,900 cfs.
“We’re a little prone if (the river) goes above 2,000 cfs, but it hasn’t happened since they built the dam,” Linfield said, adding, “With the snowpack and the unpredictability … it’s difficult to walk the line” of filling the reservoir without it spilling.
Despite the security the dam provides to riverbank Silverthorne residents, Denver Water officials announced Friday that it might not be able to prevent flooding on the Blue River below Dillon Reservoir as record-high mountain snowpack continues to melt.
Using forecasted inflows and draws through the Roberts Tunnel, “we can do some arithmetic and feel pretty confident that we’re going to fill and spill,” Steger said. He added that he anticipates inflows will keep rising.
Water has been flowing into the reservoir at a rate normal for early June at about 1,700 cfs, but forecasters say it could grow dramatically in coming days – possibly exceeding the record of 3,408 cfs set in 1995, the Denver Post reported.
Denver Water has been drawing down the reservoir to prepare snowpack that’s anticipated to melt quickly. It bottomed out at an elevation of 8,992.45 feet, or 187,916 acre-feet, on June 1.
Typically, the reservoir sits at about 238,000 acre-feet on June 1, Steger said. The last time it was purposefully drawn down for similar snowpack conditions was 1995, when on June 1 it sat at 182,855 acre-feet. It was at 173,128 acre-feet in 2003, when the area was recovering from the 2002 drought.
The National Weather Service had all of Summit County in a flood advisory through about midnight Wednesday. The advisory was expected to be lifted with cooler temperatures in the area, though meteorologist Kyle Fredin said some precipitation in the forecast could balance out the lower temperatures and continue to aid snowmelt.
Areas of particular concern for flooding are the Blue River above and below the Dillon Reservoir, Ten Mile Creek in Frisco, Hamilton Creek north of Silverthorne and Straight Creek near Dillon, Fredin said.
On Tuesday, Straight Creek was at 5.2 feet, and its action stage is 5.5 feet.
“If it continues to rise, we’ll be at the action stage by (June) 10 or 11,” Fredin said. “I don’t doubt some of these creeks will go above bank full.”
The Blue River below the dam was at 3.1 feet on Wednesday, and its action stage is 3.5 feet. Flood stage is 4 feet, or about 1,650 cfs, and the major stage is 7 feet.
“It has a ways to go,” Fredin said. “It looks like it has capacity.”
Weather service officials say it’s unlikely that flooding this year will reach 100-year or 500-year flood marks without substantial rainfall.
“Even though we have a lot of water, the terrain can handle it,” Fredin said.
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