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


    Project participants enter the federal permitting process and U.S. Bureau of Reclamation holds three formal "scoping" meetings.
  • 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


    U.S. Bureau of Reclamation publishes the Draft Environmental Impact Statement.
  • 2009


    Municipal Subdistrict offers West Slope benefits to facilitate project implementation.
  • 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


    Grand County and the Municipal Subdistrict board approve agreements to create improvements to the Colorado River. Grand County issues 1041 permit.
  • 2014


    U.S. Bureau of Reclamation issues its Record of Decision and signs a carriage contract to transport water to Chimney Hollow Reservoir.
  • 2016


    Colorado issues a 401 Water Quality Certification.
  • 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 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

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    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

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    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.