GRAND COUNTY WATER

History:

This tunnel is the main tunnel in the largest transmountain water project in Colorado, the Colorado-Big Thompson Project (C-BT).  Northern Colorado Water Conservancy District owns and operates this tunnel.  It is 13.1 miles long and runs under the Continental Divide and passes through Rocky Mountain National Park.  Construction started in June 1940 and was completed in June 1944, but the first water was not delivered until 1947.  When the two crews (east slope and west slope) met in 1944 they were off by less than a width of a penny. The west portal of the tunnel is by Grand Lake near the East Inlet Trailhead and the east portal is on the Front Range at Mary’s Lake (see map to the left).  The water that fills this tunnel is diverted from the Colorado River, Williams Fork and the Fraser River.  The west slope water delivered to the Front Range is used to generate electricity and the surplus is sold.  The tunnel can carry water at a flowrate of 550 cubic feet per second for an annual total of 213,000 acre feet.  The tunnel cost $12.8 million to construct.  The tunnel is named for a Colorado Senator who convinced Congress to fund the C-BT project.  It is the longest tunnel in the United States that provides water for irrigation.