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E-Newsletter | January 2023 |
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 Inlet/Outlet Tunnel (left), Bald Mountain Interconnect (center) and Main Dam (right)
Key Milestones Hit at Chimney Hollow Reservoir in 2022
Chimney Hollow Reservoir construction crews made significant progress in 2022. Work started in August 2021 and is scheduled to continue until August 2025. Here are some highlights from this year’s work.
Main Dam Foundation Prep: In November 2022, crews completed the main dam rock excavation, which marked a huge milestone in reservoir construction after 15 months of work on this component.
Hydraulic Asphalt Core: Chimney Hollow construction crews began the asphalt placement in October 2022. For the next two years, the asphalt will be placed in 9-inch increments per lift until the dam reaches a height of about 350 feet. Rockfill and filter/drain construction occur concurrently to complete the embankment construction at any given elevation.
Bald Mountain Interconnect: One of the most time-sensitive aspects of the Chimney Hollow Reservoir Project was the Bald Mountain Interconnect. A shutdown of the Colorado-Big Thompson (C-BT) Project occurred from mid-September through mid-December as crews cut into existing infrastructure to tie in a 126-inch diameter section of steel pipe with a 72-inch diameter steel offtake (known as a wye) to add the ability to deliver water into Chimney Hollow Reservoir from the C-BT Project.
Larimer County and Saddle Dam Access Roads: On Nov. 15, the Larimer County and saddle dam access roads were completed. When the reservoir opens to the public, the Larimer County access road will be the entry road to Chimney Hollow’s future public recreation and open space facilities. The saddle dam road is not a public road and extends to the saddle dam for Northern Water maintenance access.
Downstream Tunnel and Valve Chamber: The downstream tunnel portal and excavation of the 26-foot diameter downstream portion of the tunnel, which runs 667 feet to the center of the main dam was completed in October 2022. A 30-foot diameter valve chamber was also excavated to provide room for mechanical equipment installation and maintenance. A 72-inch diameter steel conduit will be placed inside the tunnel to bring water in and out of Chimney Hollow Reservoir.
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Windy Gap, Firming Project Provide Important Water Supplies
Due to rapid population growth during the late 1960s, six Front Range communities formed the Northern Water Municipal Subdistrict in July 1970 to plan, finance, build and operate the Windy Gap Project. The six original Windy Gap participants included Boulder, Estes Park, Fort Collins, Greeley, Longmont and Loveland.
Windy Gap Project construction began in July 1981, was completed in 1985 and began delivering water to Municipal Subdistrict participants that same year.
The Windy Gap Project is located in Grand County on Colorado’s West Slope. The project consists of a diversion dam on the Colorado River, a 445-acre-foot reservoir, a pump plant and a six-mile pipeline to Lake Granby. Windy Gap water is pumped and stored in Lake Granby, part of the Colorado-Big Thompson Project, before it is delivered to water users via the C-BT system.
The Windy Gap Project was designed to deliver an average of 48,000 acre-feet of water per year to its participants. However, during wet cycles Lake Granby is often full, leaving little or no space for Windy Gap water, since the Colorado-Big Thompson has more senior water rights. Additional storage has been contemplated since the Windy Gap Project’s inception and today, nine municipalities, two water districts and a power provider work together to build a new reservoir to store this water and make the Windy Gap water deliveries more reliable.
As population in Northern Colorado continues to grow, the region needs collaborative projects to help meet its future water demands while also protecting the environment and wildlife, maintaining local food production, and preserving the region’s quality of life. Those are precisely the objectives of the Chimney Hollow Reservoir Project, which is the main component of the overall Windy Gap Firming Project. The new reservoir will be located just west of Carter Lake in southern Larimer County and will store 90,000 acre-feet of water when built — slightly smaller than neighboring Carter Lake (112,230 acre-feet). The project will provide a firm (more reliable) yield of 30,000 acre-feet annually, which will meet a portion of the future demands of the participants.
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Chimney Hollow Water Recipients
The Chimney Hollow Reservoir Project will benefit nine cities, two water districts and a power provider. By 2050, these water providers' combined population will have far more than doubled what it was in 2005, to about 825,000 people. Water demand projections show a shortage in supply of 64,000 acre-feet in 2030 and 110,000 acre-feet by 2050.
To address this shortage, participants are relying on multiple approaches: conservation, reuse and additional storage — including building Chimney Hollow Reservoir.
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 Construction Teams
In a typical day on site, about 350 personnel come in and out of the security gate at Chimney Hollow Reservoir, which includes all the office and field staff. Northern Water is the project owner and has four employees on site daily, along with many others working on the project offsite. To complete the project, Northern Water has partnered with the following companies:
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Barnard Construction, based in Bozeman, Montana, is the general contractor. It employees the largest number of personnel on site and hired many subcontractors to help during construction, including many local hires.
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Black & Veatch, based in Overland Park, Kansas, is the construction manager. Approximately 12 employees are on site, with others working on the project remotely or from area offices. Black & Veatch subcontracted Kleinfelder, based in San Diego, California, to help with the on-site materials testing labs. Kleinfelder has about 5 personnel on site, with others working remotely.
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Stantec, based in Edmonton, Canada, is the design engineer. The on-site team consists of about six employees, with others working on the project remotely or from area offices.
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IN OTHER NORTHERN WATER NEWS
Northern Integrated Supply Project Achieves Major Milestone from Federal Agency
The U.S. Army Corps of Engineers has issued a federal Clean Water Act Section 404 Record of Decision for the Northern Integrated Supply Project. This is a major milestone for NISP, as it reflects the lead federal regulatory agency’s review and approval of the project.
The Corps’ approval was based on a lengthy and rigorous scientific analysis under the National Environmental Policy Act and a host of other environmental laws, including the federal Endangered Species Act, National Historic Preservation Act, State Water Quality compliance certification, and State Fish and Wildlife Mitigation Plan requirements.
The Corps has concluded that the project’s 40,000 acre-foot yield will meet a substantial amount of the 15 Northern Front Range participants’ future water need and that NISP is the least environmentally impactful means of satisfying that need. The Corps considered a range of other potential alternative approaches, including the adverse impacts to the region if no federal action was taken.
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Stay Connected
Visit the Chimney Hollow Reservoir Project website for the latest news and project highlights.
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About Chimney Hollow Reservoir
The Chimney Hollow Reservoir Project is a collaboration between 12 Northeastern Colorado water providers to improve the reliability of, or make firm, water supplies from the Windy Gap Project. Chimney Hollow Reservoir will be located just west of Carter Lake in Larimer County to provide dedicated storage to supply a reliable 30,000 acre-feet of water each year for future generations.
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