Colorado-Big Thompson Project fall operations update

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From email from Reclamation (Kara Lamb):

It’s that time of year again: maintenance season for the Colorado-Big Thompson Project. If you are receiving this e-mail it is because our maintenance schedule will be affecting a reservoir or river flows in which you are interested. Because all of these operations tie together, it’s a lengthy e-mail, so please bear with me:

Monday, Nov. 5: We will stop diverting through the Adams Tunnel. This will temporarily slow the draw on Granby Reservoir because we will not be pumping up to Shadow Mt. Reservoir and the Tunnel. Releases from Granby to the Colorado River should remain at or above 20 cfs at the Y gage for the rest of the calendar year.

This same day, we will also stop moving water from Lake Estes through the Olympus Tunnel to the southern power arm of the C-BT so we can start some regular maintenance projects on that section.

Water that would normally hit those three power plants will instead be released from Olympus Dam to the Big Thompson River, bumping its flows up from around 40 cfs to 150 cfs. We will change the release from the dam in the early morning hours of Nov. 5 before 5:30 a.m.

The project water released to the Big T River will be recaptured at the Dille Diversion Dam in the narrows section of the canyon. The Dille redirects the water back on course to Horsetooth Reservoir via the Charles Hansen Feeder Canal.

With 150 cfs being released from Lake Estes and no water coming in, the water level elevation at Estes will start to drop a little over a foot a day for about a week.

Monday, Nov. 12: The water level at Lake Estes will hit an elevation of about 7460 feet by day’s end. We will hold it there until the second week of December.

While water through the tunnels is off and the Lake Estes water level is down, our maintenance work will be on. During this same time, the Estes Sanitation District will be performing sand removal from the western side of Lake Estes.

Water levels at Marys Lake will not be drawn down this year.

Nov. 13: Delivery of C-BT water from Olympus Dam to Dille Dam via the Big Thompson River will stop. Releases to the river will go back to around 40 cfs—the typical native flow of the Big Thompson River this time of year. We will start delivering C-BT water from Pinewood Reservoir.

Pinewood, downstream of Lake Estes and Olympus Dam on the C-BT’s southern power arm, will stay at a high water elevation through the first part of the maintenance work. With no water coming from the West Slope, it will take over the role of delivering project water when Lake Estes hits its 7460 foot water level elevation. Because Pinewood’s own water levels are currently high, residents near and visitors to Pinewood will likely not notice its water level start to decline until the last week or two of November. It will continue to drop until the first week of December.

Dec. 7-14: All annual maintenance projects scheduled for this fall on the C-BT start to wrap up. Diversions through the Adams Tunnel will resume, the water level elevation at Lake Estes will start to rise, and it will resume delivering water through Olympus Tunnel to the southern power arm. Pinewood’s water elevation will start to come back up.

Deliveries to Horsetooth Reservoir will experience a slowdown during the middle of the maintenance work, but continue through December. The reservoir will officially start to refill in mid-to-late December, as is its normal schedule.

More Colorado-Big Thompson Project coverage here.

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