March 12, 2025

Colorado-Big Thompson Project Positioned for Water Delivery Season

Through the winter months, the Colorado-Big Thompson (C-BT) Project focuses on filling reservoirs for the upcoming water year and generating hydropower. At this time of year, the Alva B. Adams Tunnel, which diverts water under Rocky Mountain National Park from the West Slope to Northeastern Colorado, is operating at a full 550 cubic feet per second (cfs) sending water to Carter Lake and Horsetooth Reservoir. Both Carter and Horsetooth will reach capacity by late spring or early summer.  

“In the summer, demand for water outpaces Northern Water’s ability to fill reservoirs back up, which is normal for reservoirs in the West,” said Water Resources Engineer Brian Craig. “We use the winters to fill and stage them for summer when demands outpace the ability to fill again.”  

With all the water movement during winter, the C-BT Project produces a lot of energy through its six hydropower plants. The C-BT Project’s six original power plants generate power as the water moves through the system on its way to customers in Northeastern Colorado. Power is generated by water flowing through power plant turbines to produce hydroelectricity. The U.B. Bureau of Reclamation, the federal partner for the project, operates and maintains the hydropower plants.  

Carter Lake covered in snow in the winter
Snow-covered Carter Lake

“We call this the ‘power arm,’” Craig said, adding that on average, these power plants generate 770 million kilowatt-hours of renewable energy per year, which is enough to power 68,000 homes.  

Winter is also a busy season for maintenance on the C-BT Project since water deliveries slow down or stop altogether. Crews complete annual inspections and any necessary maintenance and repairs on the infrastructure to keep operations moving in the delivery season. This includes flushing canals in preparation for April 1, which is considered the official start of the new water delivery season.  

Despite a dry start to the 2024-2025 winter season, snowpack reports after recent storms show that levels are at or above the median, so Carter Lake and Horsetooth Reservoir are on track to fill to capacity in April.