Dillon Reservoir fills to 100% capacity
Water releases increase to Blue River but not enough for commercial rafting
Editor’s note: This story has been updated to correct the time frame of data collection for the Copper Mountain snow-water equivalent measurement site.
Dillon Reservoir is now 100% full, according to Denver Water, which manages the reservoir.
Nathan Elder, manager of water supply for Denver Water, said it’s normal for the reservoir to be full this time of year, but he noted that the reason it’s full despite an ongoing drought is because the water is carefully managed, and much less water was released from the reservoir to the Blue River than in an average year.
“This year, it’s been dryer than normal, so it did fill a little bit slower, and we released much less out of the reservoir to the Blue River than we typically would to ensure that Dillon would fill this year,” Elder said.
Elder said this was a year where the reservoir started out lower than normal and less water flowed in from the melting snowpack.
Water from Dillon Reservoir flows into the Blue River and Roberts Tunnel, Elder said, which carries water underneath the Continental Divide, making its way to the South Platte Basin, then to Denver Water treatment plants and finally to customers along the Front Range. The Blue River brings water to Green Mountain Reservoir and eventually to the Colorado River.
Elder noted that Denver Water is bringing much less water through the Roberts Tunnel than it typically would because of good moisture levels in the South Platte Basin, which is at 96% of normal, and water conservation by consumers on the Front Range.
“We’ve had really low demand so far this spring on the east slope side,” Elder said.
While more water is being released into the Blue River now — 184 cubic feet per second as of Wednesday afternoon compared with 100 cfs prior to Monday — it’s still not enough for rafting this year. Elder said a flow of 500 cfs is needed for rafting, but the maximum outflow this year will likely only get to about 250 cfs.
The main reason water levels are low this year is because the snowpack was below average. According to a measurement site at Copper Mountain, the 2021 snowpack peaked at 12.4 inches of snow-water equivalent, or the amount of water held in the snowpack. That’s nearly 5 inches less than the 17.3 inch median for the site, which is based on 30 years of data.
Recent rain has helped slightly but isn’t as much of a determining factor as snowpack.
“That definitely helps. It doesn’t help as much as snowpack, but it does help,” Elder said. “With that rain, we added about 573 acre feet to the reservoir over the weekend. … We had (June) 24, 25 and 26 with significant rain events.”
Dillon Reservoir holds 257,000 acre feet. Elder said the additional 573 acre feet is important but isn’t a major contribution. Compared with streams, the reservoir was able to better capitalize on rainfall due to its larger surface area.
Treste Huse, a senior hydrologist at the National Weather Service in Boulder, said stream flows in Summit County overall are below normal compared with historic levels. Huse said all streams in Summit County are below normal and that Straight Creek is running much below normal — 13 cfs Wednesday near Dillon compared with an average of 55 cfs for the same date. Recent precipitation levels have been above normal, but it hasn’t made much of a difference, Huse said.
“The snowpack drives (stream flow), and although that rainfall was helpful, it didn’t help a lot,” Huse said.
In the past 30 days, the Dillon weather station has recorded 1.69 inches of precipitation — 50% above the normal 1.13 inches in the same time period. And in the past four months, precipitation is slightly above normal. Huse said that while precipitation is above normal, the difference is less than an inch, and with dry soil conditions, it doesn’t make much of a dent in the water supply.
“There’s still a big concern with water supply,” Huse said.
Huse noted that while Summit County’s drought conditions have improved, the northern half of the county is still in a severe drought.
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