The addition of water storage is a key component of the Colorado Water Plan. Our population continues to grow as climate change brings higher temperatures and greater precipitation variability to the Colorado River headwaters. Construction of Chimney Hollow Reservoir gives the regional Windy Gap Firming Project participants a reliable water supply during dry years.  

Since the Windy Gap Project was envisioned, water managers have recognized the need for additional storage specifically dedicated to storing Windy Gap water. Currently the Windy Gap Project depends on Lake Granby to store water when the project’s water rights are in priority. However, Lake Granby’s first priority is to store Colorado-Big Thompson Project water.  

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. 

Northern Water’s Municipal Subdistrict and Larimer County cooperated to purchase the Chimney Hollow property in 2004 from Hewlett-Packard. Chimney Hollow Reservoir will provide a much-needed outdoor recreational opportunity that can be enjoyed by everyone in Northern Colorado. 

In recent weeks crews have been preparing the site for construction by bringing water and power to temporary administrative offices. In addition, the Western Area Power Administration relocated a high voltage power line from the footprint of the reservoir to a location up the hillside to the west. 

Full dam construction activities are planned to begin Aug. 16. Barnard Construction Co. Inc. of Bozeman, Montana, is the general contractor for the four-year project. The cost of dam construction is estimated at $500 million, with the complete project including West Slope improvements at $650 million. The 12 project participants are paying its cost. 

When the dam is built, it will rise about 350 feet off the dry valley floor. The dam incorporates a technology common in Europe but less so in the United States. Its water-sealing core will consist of a ribbon of hydraulic asphalt instead of the clay that serves that purpose at the Carter Lake and Horsetooth Reservoir dams. Geologists discovered there wasn’t enough high-quality clay material within the footprint of Chimney Hollow Reservoir, and instead of bringing it in from elsewhere, the hydraulic asphalt core option was chosen. The dam’s rock-fill shoulders will use material mined from the reservoir footprint, which will reduce costs, pollution and increase storage capacity. 

This new storage project allows us to supply clean water reliably, even in times of drought, to the people of northeastern Colorado from the existing Windy Gap Diversion. Starting construction on Chimney Hollow Reservoir is a major step to address water supply shortages for our growing population, much like our visionary predecessors did for us, while demonstrating that modern storage projects can also improve the environment.   

Northern Water, a public agency created in 1937, provides water for agricultural, municipal, domestic and industrial uses for more than 1 million people in Northern Colorado via the Colorado-Big Thompson Project, Pleasant Valley Pipeline and Southern Water Supply Project. It also generates hydropower at two sites and provides water quality services throughout the region. Its Municipal Subdistrict delivers water through the Windy Gap Project. Northern Water and the Municipal Subdistrict are currently building the Windy Gap Firming Project and developing the Northern Integrated Supply Project to enhance Front Range water supplies for the future.