As workers at Chimney Hollow Reservoir start the final push to complete the project in 2025, one major component is about to be crossed off the to-do list. The $10 million Chimney Hollow saddle dam, 2.5 miles south of the main dam at the head of the valley, is slated for completion in December. 

Unlike the main dam, which has a water-tight core made of asphalt, the 40-foot-tall saddle dam has a core made of clay harvested from the footprint of the reservoir. This type of clay-core, rockfill dam is common in Colorado. Dams such as those used at Horsetooth Reservoir and Carter Lake share that design, albeit on a larger scale. 

Much of the work for the saddle dam occurred in 2024, including the development of the foundation, grouting of the subsurface, placement of instrumentation and construction of the embankment. 

While the saddle dam is only 40 feet tall, it will allow the reservoir to store 27,000 acre-feet of water more than if the original topography had been the limit of the reservoir’s elevation. That is equivalent to 30 percent of the capacity of the reservoir, and it allows the project participants to achieve the 30,000 acre-foot annual firm yield of the project.