On March 15, crews holed through to connect the downstream and upstream portions of the inlet/outlet tunnel, which will play the critical role of filling the reservoir and making deliveries to water users. Although a much smaller scale, it was a stark resemblance to 80 years ago on June 10, 1944, when crews working from both the West and East slopes holed through the Alva B. Adams Tunnel. As the linchpin of the Colorado-Big Thompson Project, the 13.1-mile-long Adams Tunnel enables Upper Colorado River Basin water to flow beneath Rocky Mountain National Park to East Slope water users. 

The Chimney Hollow milestone was just under two years in the making as crews performed the first cut on the downstream portion of the tunnel on April 4, 2022. The downstream portion required about seven months of excavation, which runs to the center of the main dam. Crews headed to the other side of the dam to begin working on the upstream portion of the tunnel to connect with the downstream section to form the full inlet/outlet tunnel. 

Water will be brought in and out of Chimney Hollow Reservoir through a steel conduit built inside the tunnel under the right (east) abutment of the main dam.