Revitalizing an Important Transmission Pipeline 

In 1902, railroad pioneer David Moffat conceived a better, shorter route from Denver to Salt Lake City. His Moffat Tunnel provided rail access and included a smaller pilot hole, eventually acquired by Denver Water and used to carry water beneath the Continental Divide from the West Slope to the Colorado Front Range.

The 72-inch welded steel Siphon 1 Aerial Pipeline transports water from the west side of the Fraser River to the Moffat Tunnel. After more than 80 years of operation, the aerial pipe was showing signs of distress, and its owner grew concerned with slope stability, public safety and a possibility of accidental damage. 

The new aerial crossing revitalizes the pipeline. Underlain by loose, unconsolidated muck from the original tunnel construction, the team installed unique micropiles to overcome settlement and slope stability concerns to support the piers. The slender, decorative piers above ground are designed to reduce detractions from the area’s scenic beauty. They’re topped with elastomeric bearings — often used on bridges for seismic activity — to accommodate thermal expansion, which could lengthen or shorten the pipeline by as much as three inches. A new soil nail wall, constructed from the top down, extends five feet below the riverbed to prevent scour from undercutting the riverbank. 

With the pipeline spanning over a Gold Medal Trout habitat and located in one of America’s most popular ski resorts, the project team and Denver Water worked alongside the resort to limit disruptions by scheduling construction around major events and high-activity periods. In the Fraser River, the team diverted water and built the soil nail wall while maintaining river flows. Once complete, the team restored the river’s natural riffle-pool character, repurposed excavated material and installed native vegetation. 

Beneath the adjacent roadway, the aerial pipeline rested atop a buried anchor block with a shallow foundation. The roadway traffic above and anchor block settlement contributed to pipeline deformations. The project team installed a new anchor block with a micropile foundation and replaced the structural slab to bridge over and protect the pipeline from future deformations. 

Completed on budget and on schedule, the project team re-established the riverbed before trout spawning season and finished all work and site restoration before the first snowfall and the ski season started.