The Alva B. Adams Tunnel is a component of the Colorado – Big Thompson (C-BT) Project
About the Project
The Colorado-Big Thompson Project captures snowmelt runoff each year on Colorado’s Western Slope and is pumped from Grand Lake, the largest natural lake in the state of Colorado,and sends the water through this tunnel Under The Continental Divide for delivery to the Eastern Slopes where it is then distributed to reservoirs and farmers.
Water moves through the C-BT runoff collection system, which includes three reservoirs and a lake, by two canals and two pump plants. The project also includes Green Mountain Reservoir, which was built to benefit the West Slope.
The Alva B. Adams Tunnel begins at Grand Lake and extends to a depth of 3,800 feet under the Continental Divide for delivery of water to Northeastern Colorado. When you are at the cache site, look for the sign that illustrates the vastness of this water collection and supply network and you will see where it starts in Grand Lake, goes under the Continental Divide, and provides water for Lake Estes in Estes Park and many other reservoirs along the Eastern slopes.
The project, which cost $160 million, was constructed between 1938 and 1957. Northern Water operates and maintains most C-BT water features, while the Bureau of Reclamation operates the power facilities. The US Forest Service manages recreation at the Grand County Reservoirs.
Alva B. Adams Tunnel
Water travels to the East Slope beginning at the West Portal of the Alva B. Adams Tunnel at Grand Lake, right in the area where you will be standing when you find this cache. The tunnel drops 109 feet in elevation from west to east, allowing water to flow through by gravity in about 2.5 to 3 hours.
Construction began on the Adams Tunnel on June 23rd, 1940. Crews bored the tunnel simultaneously from each portal; when they meet, alignment was off by less than a half of an inch. Water first flowed through the tunnel on June 23rd, 1947, which was exactly seven years after the tunnel construction was started.
The tunnel’s namesake is Alva B. Adams, a US Senator in the 1940’s from Colorado who played a key role in convincing Congress the project was needed. And thanks to this project, we have Lake Granby and Shadow Mountain Reservoirs to enjoy in close proximity to Grand Lake.
Flow Capacity: 550 cubic feet per second
Diameter: 9 feet, 9 inches
Construction Cost: $12.8 million
Depth: 3,800 feet below the Continental Divide
Note: Most of the information provided in this Summary and Description was copied from the local landmark sign near the tunnel.