History

Firming Water Supplies from the Original Windy Gap Project

The Windy Gap Project was first proposed in 1967 by the cities of Boulder, Estes Park, Fort Collins, Greeley, Longmont and Loveland. Built between 1981 and 1985 and located on the West Slope near Granby, Windy Gap consists of a diversion dam on the Colorado River, a pump plant and a 6-mile pipeline to Lake Granby, the largest storage reservoir in the Colorado-Big Thompson Project system.

The Windy Gap Firming Project, of which Chimney Hollow Reservoir is a main component, will improve the reliability of, or firm, water supplies from the original Windy Gap Project, which started delivering water in 1985. It was understood the original Windy Gap Project would require additional storage to achieve firm water supplies. The Windy Gap Firming Project has been reviewed under the federal National Environmental Policy Act. This review started in 2003. NEPA and Colorado's requirement for a plan focused on fish and wildlife are among several processes in place to identify mitigation measures that will address the project's impacts. 

  • 2003
    2003
    Project participants enter the federal permitting process and U.S. Bureau of Reclamation holds three formal "scoping" meetings.
  • 2005
    2005
    U.S. Bureau of Reclamation published two reports, one describing the purpose and need, and one identifying a range of alternatives that could meet the needs.
  • 2008
    2008
    U.S. Bureau of Reclamation publishes the Draft Environmental Impact Statement.
  • 2009
    2009
    Municipal Subdistrict offers West Slope benefits to facilitate project implementation.
  • 2011
    2011
    State officials approve the fish and wildlife mitigation plan and voluntary enhancement plan
  • 2011
    U.S. Bureau of Reclamation publishes the Final Environmental Impact Statement.
  • 2012
    2012
    Grand County and the Municipal Subdistrict board approve agreements to create improvements to the Colorado River. Grand County issues 1041 permit.
  • 2014
    2014
    U.S. Bureau of Reclamation issues its Record of Decision and signs a carriage contract to transport water to Chimney Hollow Reservoir.
  • 2016
    2016
    Colorado issues a 401 Water Quality Certification.
  • 2017
    2017
    U.S. Army Corps of Engineers issues its final Record of Decision.
  • 2019
    December 2019
    The Board of Directors of the Northern Water Municipal Subdistrict chooses a contractor to build Chimney Hollow Dam. Barnard Construction Inc. of Bozeman, Mont., will enter into a $485.4 million contract that calls for the construction of a 355-foot-tall asphalt-core dam in the valley west of Carter Lake in southern Larimer County.
  • 2020
    Dec. 10, 2020
    Federal Court rules in favor of the Windy Gap Firming Project, clearing the way for construction of Chimney Hollow Reservoir near Berthoud.
  • 2021
    April 21, 2021
    The Subdistrict reaches an agreement with several environmental groups settling the lawsuit and appeal. The $15 million settlement will benefit aquatic habitat on the West Slope. The settlement will allow construction of Chimney Hollow Reservoir beginning in August 2021.
  • Aug. 6, 2021
    Eight Northern Water Directors shovel dirt at the Chimney Hollow Groundbreaking in August 2021.
    The Northern Water Municipal Subdistrict breaks ground on Chimney Hollow Reservoir, culminating a 20-year permitting process. Chimney Hollow Reservoir is a key component for these Windy Gap Firming participants: Broomfield, Platte River Power Authority, Loveland, Greeley, Longmont, Erie, Little Thompson Water District, Superior, Louisville, Fort Lupton, Lafayette and Central Weld County Water District. Each of the reservoir project participants that provide residential water service has committed to reduce per capita water supply through water conservation.
  • Aug. 16, 2021
    Aerial view of the Chimney Hollow Valley looking north toward Flatiron Reservoir.
    Northern Water’s Municipal Subdistrict issued a Notice to Proceed to Barnard Construction Co. Inc. to begin construction of Chimney Hollow Reservoir. Environmental and mitigation efforts have also begun in the Upper Colorado River basin.
  • Oct. 1, 2021
    First blast at the Chimney Hollow site on October 1, 2021.
    Crews conduct the first blast at the Chimney Hollow Reservoir construction site. Blasts occur regularly, often multiple times a week, for the duration of the project.
  • 2022
    January 2022
    Foundation grouting begins on the main dam at Chimney Hollow Reservoir.
  • Feb. 9, 2022
    Bridge over the Flatiron Penstocks that will provide recreation access when the reservoir opens to the public.
    In what is described as a “milestone” day, crews install a bridge to connect two sections of a new Larimer County access road at the Chimney Hollow Reservoir construction site.
  • Feb. 10, 2022
    Crews working on the plinth under plastic during the cold, winter months.
    Initial placement of the Chimney Hollow main dam plinth begins.
  • April 4, 2022
    Man spraying water while machine cuts into the downstream portion of the tunnel on April 4, 2022.
    Tunneling of the Chimney Hollow Reservoir inlet/outlet infrastructure gets underway.
  • July 7, 2022
    Four construction workers guide in a 72-inch butterfly valve that is being held by a crane.
    Crews place the first of 61 valves on-site as part of the conduit that will bring water into the reservoir. This valve is located in the valve vault on Bald Mountain approximately 700 feet above the top of the main dam and will provide isolation between the inflows to Chimney Hollow and the Colorado-Big Thompson Project. The 72-inch diameter valve weighs 23,000 pounds.
  • Aug. 1, 2022
    Man guiding in a piece of pipe for the Chimney Hollow Conduit.
    First piece of pipeline for the conduit installed.
  • Aug. 23, 2022
    Dignitaries from across the region gather to celebrate the start of construction at the Colorado River Connectivity Channel located in Grand County. Led by U.S. Sen. Michael Bennet, leaders of public agencies and private non-governmental organizations extol the value of the project that will reconnect two segments of the Colorado River above and below Windy Gap Reservoir.
  • Sept. 15, 2022
    Crews placing the wye in place at the Bald Mountain Interconnect that will allow water to be diverted into Chimney Hollow Reservoir.
    A shutdown of the Colorado-Big Thompson (C-BT) Project goes into effect as crews cut into the existing C-BT infrastructure at the Bald Mountain Tunnel. A 126-inch steel pipe with a 72-inch steel offtake (known as a wye) is tied-in so that future water deliveries can be made to Chimney Hollow Reservoir.
  • Oct. 15, 2022
    Crews place forms on the asphalt core of the main dam to hand-place a lift of the aslphat core.
    Crews place the first section of the asphalt core. The asphalt is placed in 10-inch lifts until it reaches the top of the dam (approximately 350 feet). Rockfill occurs concurrently to stabilize the asphalt core, covering the plinth.
  • November 2022
    Crews complete the main dam rock excavation after 15 months of work on this component.
  • 2023
    March 10, 2023
    Crews place first spillway slab.
  • March 31, 2023
    Valve house exacvation
    First valve house floor slab placed. The slam is 6.5 feet thick with about 280 cubic yards of reinforced concrete per slab.
  • March 31, 2023
    Barnard Construction surpasses 1 million hours at the Chimney Hollow Reservoir construction site.
  • April 1, 2023
    Three employees working at Chimney Hollow.
    Crews begin full production on site with double shifts. All project components have begun.
  • April 11, 2023
    The main dam reaches original grade (elevation 5,545 feet), 50 feet up from the plinth.
  • April 21, 2023
    Crews placing a portion of the Chimney Hollow conduit
    Chimney Hollow conduit reaches halfway point.
  • April 27, 2023
    View from the Chimney Hollow Overlook of crews placing embankment material.
    One million cubic yards of zone 4 embankment placed on the main dam.
  • May 2, 2023
    The asphalt core paver being loaded with asphalt.
    Crews place 100th lift of asphalt on the main dam.
  • June 26, 2023
    The main dam at Chimney Hollow Reservoir hits 100 feet.
  • Oct. 25, 2023
    Water flowing through the Colorado River Connectivity Channel.
    First water flowed through the Colorado River Connectivity Channel. The new channel around Windy Gap Reservoir hydrologically and ecologically reconnected two segments of the Colorado River for the first time in approximately 40 years.
  • November 2023
    A blast in the quarry at Chimney Hollow.
    Quarry blasting hit peak production supplying the approximate 62,000 tons of material daily. This material is keeping crews busy dumping a 100 ton load every two minutes, 20 hours a day, six days a week for the next two years.
  • Nov. 8, 2023
    Grouting complete on saddle dam.
  • December 2023
    Crews placed the final section of the concrete plinth, tying the above-ground features of the dam to the grout curtain and rock foundation below. It is secured by thousands of anchors and provides a water-tight bond between the foundation and asphalt core.
  • 2024
    March 13, 2024
    A roadheader is shown in the foreground after holing through the tunnel and seeing light on the other side.
    Crews hole through on tunnel, connecting the upstream and downstream portions.
  • March 23, 2024
    Main dam hits halfway mark of 175 feet.
  • March 29, 2024
    Crews begin summer working hours, which includes two 12-hour shifts, six days a week.
  • April 2024
    Spillway construction reaches halfway point.
  • June 7, 2024
    The clay core of the saddle dam with equipment in the background.
    Saddle dam clay embankment begins.
  • June 30, 2024
    Crews placed the tie-in lift that connects two sections of the main dam, separated by a natural rise in the bedrock. The 9-inch lift was placed partially by hand and partially by the asphalt paver. It ran about 3,000 feet and took crews 11 hours to complete.
  • July 29, 2024
    View of Chimney Hollow Reservoir with smoke from the Alexander Mountain fire in the distance.
    Alexander Mountain wildfire ignites north of the site, crews evacuated.
  • July 30, 2024
    Stone Canyon wildfire ignites south of the site, crews remain evacuated.
  • August 2024
    Crews installed the 25-ton gantry crane inside the valve house that will allow access for future maintenance.
  • Aug. 5, 2024
    Crews back to work after wildfire evacuation orders lifted.
  • Sept. 2, 2024
    View of the main dam looking east shows the main dam at 250 feet.
    Main dam hits 250 feet. Only 100 feet left to go!
  • Sept. 25, 2024
    A portion of the 10-foot by 10-foot box culvert section of the spillway.
    Last slab of concrete placed for the box culvert portion of the spillway.
  • Sept. 26, 2024
    Grouting program completed.
  • October 2024
    The Colorado River Connectivity Channel that connects two segments of the Colorado River near Windy Gap Reservoir
    Colorado River Connectivity Channel (CRCC) completed. Construction got underway in the summer of 2022, and by Oct. 25, 2023, the project was far enough along to send the first flows into the new channel. The Colorado River Connectivity Channel is part of a $90 million package of environmental measures associated with construction of Chimney Hollow Reservoir near Loveland, which is where Windy Gap water will be stored once construction is complete in 2025.
  • Nov. 19, 2024
    Heavy equipment compacts clay on the saddle dam.
    Final lift of clay placed on the saddle dam.
  • 2025
    July 18, 2025
    Final lift of asphalt placed on the main dam.
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