Key Milestones Hit at Chimney Hollow Reservoir in 2022 — @Northern_Water #ColoradoRiver #COriver #SouthPlatteRiver

Inlet/Outlet Tunnel (left), Bald Mountain Interconnect (center) and Main Dam (right). Credit: Northern Water

From the Chimney Hollow “E-Newsletter” from Northern Water:

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. 

Northern Water’s Joe Donnelly and Jeff Drager explain in this video how the new 90,000 acre-foot Chimney Hollow Reservoir, located southwest of Loveland, will be filled with water once construction is completed in 2025.

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