How the Colorado-Big Thompson Project Works

  The Colorado-Big Thompson Project collects water from the upper Colorado River basin on the West Slope and delivers the water beneath the Continental Divide to Colorado's East Slope.

The C-BT Project uses a complex system of reservoirs, pump plants, tunnels, pipelines and power plants and relies on two basic forces of nature: melting snow and gravity.

80 percent of C-BT Project Water Comes From Snowmelt
More than 80 percent of the project’s water comes from snowmelt – or “runoff” – in the upper reaches of the Colorado River basin, located in Rocky Mountain National Park and Grand County, CO.

See the SnoWatch Snowpack Data pages for information about snow accumulation and watersheds.

The West Slope collection system consists of three reservoirs and one natural lake:
  • Grand Lake (natural lake)
  • Shadow Mountain Reservoir
  • Lake Granby
  • Willow Creek Reservoir
13-mile Tunnel Beneath Rocky Mountain National ParkThe C-BT Project system collects runoff and transports it beneath Rocky Mountain National Park via the 13.1-mile Alva B. Adams Tunnel to the East Slope.
  Water Flows to Five East Slope Power PlantsC-BT Project water flows by gravity – with no pumping – through the Adams Tunnel and a series of six power plants and reservoirs.

After flowing through the power system, water is stored in three East Slope terminal reservoirs:
  • Horsetooth Reservoir west of Fort Collins, CO
  • Carter Lake west of Berthoud, CO
  • Boulder Reservoir northeast of Boulder, CO
Water Distributed to Northeastern Colorado From these three reservoirs, water is distributed via a series of canals
and pipelines to more than 640,000 acres of farm and ranch land and about 895,000 people in Northeastern Colorado.

The C-BT Project consists of:
  • 12 reservoirs
  • 35 miles of tunnels
  • 95 miles of canals
  • Six hydroelectric power plants
  • 700 miles of transmission lines
C-BT & Windy Gap Project Statistics
Colorado-Big Thompson Project Map 
Water Collection and Distribution Systems Map
Map Gallery

Water Collection & Distribution Systems map - Northern Water

Colorado-Big Thompson Project profile map