Colorado-Big Thompson Project update: Releases from Granby Reservoir are 430cfs

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From email from Reclamation (Kara Lamb):

It’s that time of year we all start looking for snow to melt, rivers to run and reservoirs to fill. While every year here in Colorado presents an interesting run-off season, this one is shaping up to possibly be more memorable than others.

We’re looking at a significant snow pack average on both sides of the Divide. Despite it being nearly the end of May, snow pack continues to hang on. Typically, snow pack is measured in daily averages. So, as long as that snow doesn’t melt, the daily averages climb. Right now, we’re looking at a snow pack in the Blue River Basin up above Green Mountain Reservoir of around 353% of average.

With that in mind, we’ve been generating power at the plant and moving water out of the reservoir in anticipation of the coming snow melt. Releases from the dam of about 1200 cfs will continue through the Memorial Day weekend. The reservoir is also starting to fill, albeit slowly, at a rate of just about a foot a day.

Moving up the Colorado River into Grand County, we’re seeing snow pack in the Upper Colorado River Basin (above Granby and Willow Creek) of around 286% of average. In anticipation of the snow melt run-off, Northern Water has drawn Willow Creek Reservoir down to almost dead storage and has been adjusting releases so that outflow matches inflow. It’s been fluctuating a little bit, getting as high as 900 cfs. We’re maintaining a fairly steady release out of Granby of around 430 cfs.

If all the C-BT’s west slope storage is combined, the average for this time of year is actually up a little bit at about 104% of average.

To date, we’ve been running a full Adams Tunnel, moving water from Granby and Shadow Mountain reservoirs to the east slope into Horsetooth, Carter, and on downstream. This means that the reservoirs in the middle of the system have been operating pretty normally. Lake Estes, Pinewood, and Flatiron reservoirs are basically full, with some water level elevation fluctuation for hydro-power generation. All three of these reservoirs should operate pretty normally through Memorial Day weekend.

As I’ve mentioned before, Lake Estes is not a regulating reservoir. Flows out of Rocky Mountain National Park and the surrounding area into the Big Thompson River above the reservoir are largely uncontrolled streams. We have some flexibility at Olympus Dam, which holds back Lake Estes, but we do have to bypass, send on through, native Big Thompson river flows. We continue to balance inflow and outflow there as best we can. Last night, we dropped the releases from Olympus Dam by about 50 cfs. Right now, we are releasing about 250 cfs to the canyon. Flows in the canyon could fluctuate 50 cfs up or down through the weekend.

The pump is on to Carter Lake and its water level elevation is steadily climbing. Today, it is at a water level elevation of about 5754 feet and still going up. We are planning on continuing to pump to Carter into June.

Likewise, Horsetooth Reservoir’s water elevation continues to rise. It’s at an elevation of about 5408. While that elevation is pretty typical for this time of year (we normally start the summer season and Memorial Day weekend somewhere between 5410-5414), it is likely to continue climbing past this weekend and into June.

Meanwhile, the first holiday weekend of the summer season is almost here. I’ve attached a news release Reclamation distributed this week reminding folks to take the proper CLEAN, DRAIN, DRY precautions regarding the invasive quagga and zebra mussels.

More Colorado-Big Thompson Project coverage here.

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