2024 Project Of The Year – Connections: Daly Ditch Siphon, Aerial Span and Conveyance Welded Seam Spiral Rib

By: TrueNorth Steel

In Hamilton, MT, the wooden flume for Daly Ditches Irrigation District (DDID) helped facilitate irrigation water in the Bitterroot Valley for over a century. While beautiful, the flume’s useful design life recently came to an end. The obvious solution was to span the canyon with a modular steel bridge, but this proved to be too costly for a 200’ bridge. To meet function and budget requirements, a complete design change was needed. TrueNorth Steel first suggested a siphon to solve this problem. This solution presented its own challenges as the siphon needed to be drained at the end of every season and the canyon bottom was subject to scour from storm water runoff.

With these challenges in mind, an aerial span was then suggested. This provided a solution to the siphon drainage issue by allowing easy access to the bottom of the siphon and the recast piers were set below scour depth. The NCSPA manual was referenced to confirm pipe gauge and clear span lengths. To accommodate the length of the clear span, three precast piers were installed to support the bottom of the siphon. For corrosion protection and superior hydraulic performance, a 60” Aluminized Type II welded-seam Spiral Rib was utilized to pass the necessary volume of water through. Additionally, the welded-seam pipe, bands, and gaskets equipped with rods and lugs provided the most watertight scenario possible.

The flume along the hillside also required extensive repairs and was replaced with a 73”x55” Aluminized Type II welded-seam pipe arch to convey irrigation water and terminate back into the ditch. Precast concrete inlet and outlet structures were used to transition the different segments of the system. A steel trash rack was used to prevent debris from flowing through the system and acted as a human safeguard to prevent a person from being sucked into the siphon.

TrueNorth Steel worked closely with DDID from the project’s start to finish. We facilitated the management of project engineering and precast. From rough sketches to plans and specs to reality, this project helped provide critical infrastructure to supply the Bitterroot Valley with irrigation for many years to come.