Blue River flow is above average following rain on the Western Slope and Front Range

Extra water is too little, too late for commercial rafting in Summit County

The Blue River is pictured June 1, 2020, in Silverthorne. After a summer of low flows, the river rose more than 200 cubic feet per second from July to August.
Photo by Jason Connolly / Summit Daily News archives

Editor’s note: This story has been updated to clarify information about refilling the Goose Pasture Tarn.

The Blue River is back with an above average flow.

On July 1, the Blue River below Dillon was flowing at 221 cubic feet per second. On Aug. 5, it jumped up to 455 cfs. Nathan Elder, manager of water supply for Denver Water, explained that in the first week of August, the Blue River’s flow reached the 450 mark and has slowly declined since. On Tuesday, Aug. 10, it was 340 cfs, which he said is slightly above normal for this time of year.

Denver Water manages Dillon Reservoir, which the Blue River flows into and out of.

“We’re trying to match outflow with inflow and send that water downstream to Green Mountain Reservoir,” Elder said.

The increase in water to Green Mountain Reservoir is welcome, as the reservoir was over 50,000 acre-feet below normal in late July, and a downstream call for irrigation rights was placed on the reservoir. As of Aug. 11, the reservoir, which is full at about 154,000 acre-feet of water, was holding 100,243 acre-feet of water.

Summit County saw its wettest July in 10 years, which is what has contributed to the increase in outflow, Elder said. He noted that not only has the rain on the Western Slope helped, but rain on the Front Range has lowered water demands on that side of the Continental Divide. That has reduced the need to send water through Roberts Tunnel, which has kept more water in Dillon Reservoir and made way for the release of more water down the Blue River and into Green Mountain Reservoir.

“We started out really, really dry,” Elder said about this season. “We didn’t have a huge snowpack, and we barely filled the reservoir. And then we got a lot of that excess precipitation in July that allowed us to keep the reservoir full and even start spilling.”

Dillon Reservoir started out the year lower than normal, and less water flowed in from the melting snowpack. In late June, Elder reported that the reservoir was full but only because much less water was released from the reservoir to the Blue River than in an average year. The lack of water flowing into the Blue River meant two things: Less water went to Green Mountain Reservoir, and commercial rafting couldn’t happen on the river this year.

“It’s been a difficult struggle to manage Dillon,” Elder said. “And we got lucky with some precipitation on the east slope that reduced demand and allowed us to reduce our tunnel demands from what we were expecting, and also monsoons on the west slope above Dillon that helped fill the reservoir and keep it full longer — so it’s a combination of both of those things that have helped.”

Performance Tours Rafting owner Kevin Foley previously reported that commercial rafting operations like his only send out guided trips on the Blue River if river flows are a minimum of 500 cfs. The company has been leading commercial trips on the Arkansas River this year.

On Wednesday, Aug. 11, Lauren Swanson, spokesperson for Performance Tours, wrote in a text that the company’s rafting season is coming to a close. While the commercial season is winding down, Swanson said they’re hoping for a strong winter snowpack to run operations on the Blue River next June.

As for the Goose Pasture Tarn, which is currently lowered due to the rehabilitation of the dam, Elder said the tarn’s water that is being stored in Dillon Reservoir has a “very small impact.” For context, the tarn is 771 acre-feet, whereas Dillon Reservoir is over 257,000. Once it’s time for the tarn to be refilled, it will be given priority for water rights.

Graphic shows the changes in streamflow of the Blue River below Dillon Reservoir over the past three years.
Taylor Sienkiewicz/Summit Daily News


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