The project to construct a new reservoir in Northern Colorado has been in the works for close to a quarter-century and, last Friday, a major step was taken when the official ground-breaking was held at the site of the future Chimney Hollow Reservoir, just west of Carter Lake.

Courtesy photo The Municipal Subdistrict Board of Directors of the Chimney Hollow Reservoir officially breaking ground at a ceremony last Friday. The project to build the new 90,000 acre reservoir just west of Carter Lake has been in the works for more than 20 years and is expected to take four years to complete.

“Today marks a long-awaited milestone that required years of hard work and cooperation among many groups with diverse interests to achieve a project that has benefits for everyone in Colorado,” said Berthoud-based Northern Water General Manager, Brad Wind.

The planning, permitting and legal challenge process was compared to a maze with many unforeseen obstacles along the way, according to Northern Water Municipal Subdistrict president, Dennis Yanchunas, who spoke to the assembled crowd during the ground-breaking ceremony.

The permitting process for the Chimney Hollow project began in 2003 but the conception of the reservoir itself dates all the back to the 1950s. Once complete, the reservoir will hold up to 90,000 acre-feet of water and will supply 30,000 acre-feet of water for the more than 500,000 residents of Northeastern Colorado. According to Aaron Rietveld, of Montana-based Barnard Construction which is serving as the general contractor for the project, completion of the reservoir is expected in four years, potentially slightly quicker.

The project will represent the largest mining operation in Colorado, removing in the neighborhood of 63,000 tons of rock per day to fill the shoulders of the dam, reducing costs, pollution and increasing storage capacity. The dam itself, which will rise 350 feet from the valley floor on the northern side of the reservoir, is a revolutionary design that consists of an asphalt core. The technology of asphalt core dams is common in Europe but very rare in the United States.

According to the information provided, the hydraulic asphalt core will be used in lieu of clay (which is used for the dams at both Carter Lake and Horsetooth Reservoir) as geologists involved in the planning process discovered there was not enough quality clay in the area to provide the needed materials.

According to Chimney Hollow Reservoir website, “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 (CBT) water.”

The construction of the reservoir itself is estimated to cost $500 million and will be funded by the 12 project 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. There will be an additional $150 million in expenses associated with projects on the Colorado River on the Western Slope as part of the CBT infrastructure.

Additional information about the Chimney Hollow Reservoir project can be found at https://www.northernwater.org/chrp.