Adams Tunnel West Portal

Colorado-Big Thompson Project water travels 13.1 miles to the East Slope beginning at the West Portal of the Alva B. Adams Tunnel at Grand Lake. The West Portal is near the parking lot and trailhead for the East Inlet Trail into Rocky Mountain National Park. 

The Adams Tunnel is 9-feet 9-inches in diameter and runs beneath Rocky Mountain National Park. It cuts through the Continental Divide as much as 3,800 feet beneath the earth’s surface.

The tunnel drops 109 feet in elevation between the west and east portals, enabling water to flow by gravity without pumping assistance. It takes about two hours for water to travel from the tunnel's West Portal to the East Portal.

West Portal of the Alva B. Adams Tunnel
West Portal of the Alva B. Adams Tunnel

First Water Delivered in 1947
Construction of the Adams Tunnel began on June 23, 1940. Contractors bored the tunnel simultaneously from each portal, 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. The tunnel cost $12.8 million to construct.

Tunnel Delivers 213,000 Acre Feet of Water
The Adams Tunnel has a capacity of 550 cubic feet of water per second, and delivers an average of 213,000 acre-feet of water annually to the East Slope.

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.