C-BT Infrastructure

Project Complex in Design

The Colorado-Big Thompson (C-BT) Project, while relatively simple in concept, is actually complex in its design to collect snowmelt from the Upper Colorado River basin, and deliver it as a supplemental water supply.

West Slope Collection Systems

The West Slope collection system stores Upper Colorado River watershed runoff in reservoirs before transporting it to the East Slope through the Alva B. Adams Tunnel. The collection system comprises three reservoirs, a natural lake, two pump plants and associated canals, as well as control and measurement facilities. 

The North Fork of the Colorado River enters the C-BT Project collection system on the west side of Shadow Mountain Reservoir. The Colorado River flows from Shadow Mountain to Lake Granby, and exits the southwest side of the lake at Granby Dam. 

Shadow Mountain Reservoir

East Slope Distribution Systems

Once water travels through the Alva B. Adams Tunnel and exits the East Portal, it passes through an East Slope distribution system of pipelines, canals, hydropower plants and reservoirs before it is released to farmers, industries and municipalities. C-BT Project water is stored in the distribution system’s three terminal reservoirs: Carter Lake, Horsetooth Reservoir and Boulder Reservoir. Several other East Slope reservoirs play an important role in the C-BT Project’s hydropower system.  

Carter Lake

Alva B. Adams Tunnel: Delivering Water Beneath the Continental Divide

As the linchpin of the C-BT Project, the 13.1-mile Alva B. Adams Tunnel carries water from the Upper Colorado River Basin beneath Rocky Mountain National Park to users on Colorado’s East Slope. The tunnel extends from its West Portal on the east shore of Grand Lake to its East Portal along the Wind River, about 4 miles southwest of downtown Estes Park. The concrete-lined, cylindrical tunnel measures 9 feet 9 inches in diameter and reaches depths of up to 3,800 feet beneath the Continental Divide.

A 109-foot elevation drop between the portals allows water to flow by gravity without pumping. With a capacity of 550 cubic feet per second, the tunnel delivers more than 200,000 acre-feet of water annually to Northeastern Colorado, with travel time through the tunnel averaging about two hours.

The tunnel is named for Alva B. Adams, a U.S. Senator from Colorado who played a key role in convincing Congress to fund and construct the C-BT Project. At the time it was built, the Adams Tunnel was the longest tunnel in the United States to provide water for irrigation at a cost of $12.8 million.

 

First Water Delivered in 1947

Construction of the Adams Tunnel began on June 23, 1940. Contractors bored the tunnel simultaneously from both portals, and when the two crews met on June 10, 1944, the alignment was off by less than the width of a penny. The first C-BT Project water flowed through the Adams Tunnel on June 23, 1947.  

Power for West Slope Pump Plants

Electricity from the Lake Estes Power Plant reaches the West Slope’s Farr and Willow Creek pump plants through a 69,000-volt transmission line extending the length of the Adams Tunnel. The power line, suspended from the tunnel’s ceiling, is encased in a nitrogen-charged conduit to prevent corrosion. 

Hydroelectric Power

While the primary purpose of the C-BT Project is to deliver water, it also generates hydroelectric power as water passes through several power facilities on both the East and West slopes. Through the U.S. Department of Energy, the Western Area Power Administration markets 700 million kilowatt hours on average each year. A portion of the power revenues helps repay the federal government for the costs to build the C-BT Project.

Learn More About Hydropower
Mary's Lake Power Plant