Colorado-Big Thompson Project

12

Reservoirs

35

Miles of Tunnels

95

Miles of Canals

8

Hydroelectric Power Plants

700

Miles of Electric Transmission Lines

Delivering Water to +1.1 Million People

The Colorado-Big Thompson (C-BT) Project collects, stores and delivers on average 200,000 acre-feet of supplemental water each year. Melting snowpack in the Colorado River headwaters on the West Slope is diverted through a tunnel beneath the Continental Divide to more than 1.1 million residents and 550,000 acres of irrigated farmland in Northeastern Colorado. Together with the U.S. Bureau of Reclamation, we jointly operate, maintain and fund this federally-owned project. 

C-BT Project Map

How the Project Works

  1. Planning

    Investigating and planning the C-BT Project involved a great deal of ingenuity and time exploring the mountain peaks and valleys of Colorado’s Northern Front Range. While the project incorporates a complex system of reservoirs, pump plants, tunnels, pipelines and power plants, at its core the C-BT Project relies on two basic forces of nature: melting snow and gravity. 

  2. Snowmelt

    Nearly all of the project’s water originates as snowmelt from the Upper Colorado River Basin in Rocky Mountain National Park and Grand County. About 80 percent of Colorado’s precipitation falls on the West Slope of the Continental Divide, primarily as snow. In contrast, northeastern Colorado receives only about 14.5 inches of precipitation each year—far less than the amount needed for most irrigated crops, which typically require at least twice that.

    For comparison, Midwestern states like Illinois average around 40 inches of precipitation annually, while East Coast states such as Maine receive nearly 50 inches. To manage this limited supply, snowmelt is captured and stored in Lake Granby—the second-largest body of water in Colorado. 

  3. Through the Tunnel

    From Lake Granby, water is lifted by Farr Pump Plant into the Granby Pump Canal feeding Shadow Mountain Reservoir and Grand Lake. Water then flows from Grand Lake into the West Portal of the 13.1-mile Alva B. Adams Tunnel.  

  4. Flowing by Gravity

    Once water exits the tunnel’s East Portal, it descends the Front Range mountains nearly 3,000 vertical feet and passes through five power plants and four reservoirs. The hydropower generated provides a clean, renewable supply of power for Northeastern Colorado and the Western United States.  

  5. Storage and Delivery

    Along the Front Range foothills, C-BT Project water is stored in three terminal reservoirs—Horsetooth Reservoir, Carter Lake and Boulder Reservoir. These reservoirs provide both storage and great opportunities for water-based recreation, including boating, fishing, waterskiing, swimming and more. From these reservoirs, C-BT Project water is distributed via a series of canals and pipelines to irrigated farms, as well as industries, utilities, cities, towns and rural domestic water districts. A total of 32 municipalities receive a portion of their water through the C-BT Project, along with 120 ditch, reservoir and irrigation companies.  

Interpretive Area

Although the concept of the C-BT Project is straightforward, its design and operations are highly complex. In 2003, when Northern Water relocated its headquarters from Loveland to Berthoud, the organization took the opportunity to create an Interpretive Area and water feature to help explain how the C-BT and Windy Gap projects work.

While not an exact replica, the Interpretive Area includes a recirculating water feature with 13 reservoirs, along with representations of the Continental Divide and the Alva B. Adams Tunnel. Together, these elements provide visitors with a clear, visual interpretation of the projects’ operations.

Visit the Interpretive Area
Interpretive Area in Northern Water backyard with water feature and trees.