Roberts Tunnel East Portal, Colorado

The Roberts Tunnel, one of the largest and longest water tunnels in the world, begins under the Dillon Reservoir, and flows for 23 miles, across the Continental Divide, to its eastern portal by gravity. At its east portal, 175 feet lower in elevation than its west portal, it emerges from underground just below the grade of the adjacent highway, with a small control building on top of it. It crosses under the highway, and spills into the North Fork of the South Platte River. From there the river flows into reservoirs feeding the needs of Denver.