St. Mary Canal Siphon Response Update And Next Steps

The Bureau of Reclamation continues to work closely with the Milk River Joint Board of Control, the Blackfeet Tribe, and the state of Montana to rebuild the St. Mary Canal Siphon following the catastrophic failure on June 17. Reclamation has authorized an emergency extraordinary maintenance determination and is working with partners to identify the next steps that are cost-effective and ensure a timely solution.

A technical team comprising Reclamation, Milk River Joint Board of Control, the Blackfeet Tribe, the Department of Agriculture’s Natural Resources Conservation Service, and the Bureau of Indian Affairs was set up after the breach and met on site to assess the condition of the siphon and to explore repair solutions and alternatives shortly after the site was secured. The team determined that pursuing a partial restoration of service to the St. Mary Canal Siphon would serve to slow progress toward the needed complete replacement of the siphon and is therefore not advisable.

“Reclamation is committed to this community and are grateful for the partnership from the Joint Board, the Blackfeet Nation, the state of Montana, and the Montana Congressional delegation as we move expeditiously,” said Reclamation Commissioner Camille Calimlim Touton. “Reclamation has authorized an emergency extraordinary maintenance determination in order to quickly respond to urgent infrastructure needs at St. Mary Canal. This mechanism allows us not only to expedite essential repairs to the St. Mary Canal Siphon, but also the Halls Coulee Siphon, which is also at risk of failure, in addition to our work to rebuild the St. Mary headgates and Fresno Reservoir. We will continue to work in close collaboration with our partners to support this community and our water delivery needs to the area.”

“Due to the time and costs associated with a temporary solution that would deliver only a fraction of normal diversions, Reclamation has decided to focus all efforts on complete replacement of the St. Mary Canal Siphon and Halls Coulee siphon as expeditiously as possible,” said Reclamation’s Montana Area Office manager Ryan Newman.

Reclamation and the project beneficiaries will share the total cost for replacement of both sets of siphons, currently estimated at approximately $70 million. Reclamation secured initial federal funding to begin site remediation activities, and the state of Montana made available approximately $32 million for the Milk River Joint Board of Control to begin work on the siphon replacement.

As part of a planned replacement project, Reclamation and the Milk River Joint Board of Control initiated designs for replacement of the siphons in early 2023 with HDR Engineering, Inc. leading the design.

“Having designs started, even at 30 percent to 60 percen design stage, will allow the project to move forward in an expedited fashion,” said Jennifer Patrick, Milk River Joint Board of Control’s project manager. “We still expect replacement to take into late summer or early fall of next year. Continued collaboration with Reclamation, the state of Montana, the Blackfeet Nation and a host of other agencies is critical as we all work towards returning this key piece of infrastructure to service.”

The St. Mary Canal Siphon suffered a catastrophic failure Monday, June 17, 2024, requiring Reclamation to stop water diversion to the St. Mary Canal. The St. Mary Canal is a vital component of the Milk River Project. It provides 60 percent to 80 percent of the water for irrigation and potable uses in northern Montana through a trans-basin diversion from the Hudson Bay watershed to the Missouri River basin.

The St. Mary Canal Siphon consists of two 90-inch riveted steel barrels that traverse the valley from the inlet, transition to an 84-inch diameter pipe at the river crossing, and then back to a 90-inch diameter pipe as they ascend the valley slope to the outlet. It was constructed in two phases, with the downstream barrel completed between 1912 and 1915 and the upstream barrel after 1925.

The siphon has undergone extensive repairs over time due to seepage, corrosion, and buckling. A cathodic protection system was installed in the 1950s to address these problems. However, unstable valley sidewalls have caused further movement of the steel barrels and concrete supports, leading to additional damage.

Reclamation previously awarded a contract for $88 million from the Bipartisan Infrastructure Law for the repair of the St. Mary Diversion Dam, another feature of the Milk River Project.