From email from Reclamation (Kara Lamb):
There are a few changes coming up for Carter and Horsetooth reservoirs this week. This is just a quick update on what to expect.
Carter Lake is sitting at a fairly average water elevation for this time of year. Full is around 5759 feet above sea level. Currently, the reservoir is at about 5717 feet. This is largely because we have been delivering water from Carter Lake via both the St. Vrain Supply Canal out of Carter Lake Dam #1 and through Unit #3–the reversible pump unit at Flatiron Power Plant.
Normally, Unit 3 is used to pump water up to Carter, filling it, but it can be used in reverse to generate hydro-electricity and deliver water down the Charles Hansen Feeder Canal, which runs all the way to Horsetooth. For the past month, we have been using Unit 3 to meet some water demands downstream of the canal.
That will end tomorrow. On Wednesday, September 14, Unit 3 will go back into pump mode and the water elevation at Carter Lake will likely start rising again.
Meanwhile, Horsetooth is at a water level elevation that is actually higher than average for this time of year. The reservoir is at an elevation of about 5407. All ramps are still in the water–and that is not usually the case after Labor Day.
When the pump to Carter goes on tomorrow, we will be taking a section of the canal which feeds Horsetooth down for annual maintenance. With little water coming into the reservoir, it is likely its rate of drop will increase. The rate of drop will depend on water demands, which are driven largely by the weather. Visitors to and residents around Horsetooth should anticipate that its water level will continue to go down through September and October, as is typical.
More Colorado-Big Thompson Project coverage here.