Colorado-Big Thompson Project update: Lake Granby rising about one-half foot per day

A picture named coloradobigthompsonmap.jpg

From email from Reclamation (Kara Lamb):

We’ve seen pretty steady run-off inflow and outflow at Shadow Mountain, Willow Creek and Lake Granby reservoirs the last week or two.

Shadow Mountain has seen snow melt run-off inflow pick up. As a result, we are releasing through the dam and over the spillway at times in excess of 2000 cubic feet per second. At the same time, we have also been diverting to the Adams Tunnel. But, as east slope water rights have come into priority, we have had to scale back the diversions. Meanwhile, Shadow Mountain maintains basically a full water level elevation and additional run-off inflow is passed on downstream to Granby.

Granby has seen its water level rise pretty steadily as the snow pack has come down. Right now, it’s rising at a rate of about a half a foot a day.

In a year when we don’t have as much snow pack, we would typically keep the gates to the spillway on Granby Dam closed and let the reservoir fill as close to its full elevation of 8280 as it can. With the exceptional snow pack we’ve maintained this spring, however, we’re operating a little differently. The bottom of Granby’s spillway gates are at an elevation of 8260. Northern Water already has those gates open a little bit so that as more run-off inflow comes into the reservoir this weekend, filling the last two vertical feet below the gates, it will start to push onto the spillway. We anticipate that will happen sometime Sunday.

How much water comes into the reservoir depends on how much more snow melt run-off we see this weekend.

Willow Creek Reservoir, which started the run-off season drawn to almost dead storage, has risen pretty quickly, as well. We continue to pass on through the reservoir about 1300 cfs which is flowing through the dam and down the creek. Once the reservoir fills to an elevation of 8118 (it’s just over 8116 right now), we can pump water out and up to Granby. That could happen as early as next week.

From email from Reclamation (Kara Lamb):

I’ve gotten some questions about why Pinewood Reservoir is low while snow melt run-off is under way. The reason it is lower is because we need to maintain some operational flexibility as we prepare to finish filling Carter Lake, then switch operations over to finish filling Horsetooth Reservoir.

Because Pinewood sits in the middle of the Colorado-Big Thompson Project’s southern power system, it sometimes bears the burden of providing the flexibility we need as we move water around. With one unit at the Flatiron Power Plant down below still undergoing maintenance, this flexibility is even more important.

As more of the upper mountain snow pack starts to melt and come down, however, we will see Pinewood start to rise again–that could be as soon as this weekend.

From email from Reclamation (Kara Lamb):

Just a quick note to let everyone know we’ve reached a full reservoir elevation at Carter Lake. The pump will go off tomorrow, Saturday June 11, in the morning. That means a little more water will go into Horsetooth and it will see its water level elevation continue to rise.

From email from Reclamation (Kara Lamb):

In anticipation of more incoming snow melt run-off, we will increase releases from Green Mountain Reservoir to the Lower Blue river late tonight, June 10. By tomorrow morning, June 11, flows in the Lower Blue should be around 1400 cfs.

From email from Reclamation (Kara Lamb):

Inflow to Lake Estes last night [June 9] peaked around 950 cfs. This morning, it is down to about 879 cfs. We are taking some of that water out via the Olympus Tunnel, generating hydro-electric power and sending it on its way to Horsetooth, via the Colorado-Big Thompson Project. We have curtailed project imports from the west slope accordingly. As we continue to balance inflow, storage, and priority water, releases from Olympus Dam to the Big Thompson Canyon were reduced last night around 2 a.m. by about 90 cfs. As a result, we are currently releasing about 692 cfs.

Leave a Reply