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New details about St. Mary Canal siphons failure

Posted at 4:44 PM, Jun 18, 2024

GREAT FALLS — The following information was provided in a news release from the US Bureau of Reclamation on Tuesday, June 18, 2024:

On June 17, 2024, both St. Mary River siphons experienced structural failures outside Babb, Montana. The breach caused substantial water discharge, affecting the surrounding areas. The breach led to severe erosion, resulting in washout areas at the breach site, impacting the hill and concrete footings holding the pipes. Water flows are expected to continue throughout the day. They are anticipated to subside sometime this afternoon as the canal drains.

Drone video: failure of St. Mary Canal siphon

The majority of the damage is located on lands administered by the Blackfeet Tribe. The flooding caused road closures and disruptions to utilities such as water and electricity. The community, which relies heavily on this water for agriculture, will be significantly impacted for the rest of the season. Though the Fresno and Nelson dams are nearly full, the water supply is expected to be depleted over the next several weeks.

The incident primarily impacted residents and tribal land. Hooks Hideaway, a facility in close proximity to the breach, has been affected, and livestock has been successfully relocated from the site. No injuries have been reported. The Bureau of Reclamation and Emergency Services, including local law enforcement, are actively involved in the response efforts. The Bureau of Reclamation is coordinating with local services to bring bulldozers to restore access to flooded areas. The Bureau of Reclamation's primary concern is the safety of people and property. When the flooding subsides, Reclamation will evaluate any available short-term solutions, along with long-term rebuild options.

Ryan Newman, Reclamation's Montana Area Office Manager, stated, "Our primary concern is the safety and well-being of the community. We are committed to supporting those affected and are finding solutions to restore water availability to the affected area."

Planning activities for the replacement of the St. Mary siphon were funded through the Bipartisan Infrastructure Law and were initiated in 2023. The plans for replacement of the St. Mary Siphon are currently at a 60% design stage. Geotechnical and cultural investigations were underway before winter weather set in.

'Catastrophic failure' of siphon at St. Mary Canal

The St. Mary siphon is a critical component of the Milk River Project, designed to transport water from the St. Mary River across the valley. It consists of two 90-inch riveted steel barrels traverse the valley from the inlet, transition to an 84-inch diameter at the river crossing, and then back to 90 inches in diameter as they ascend the valley slope to the outlet. The siphon has a maximum head of 165 feet and was constructed in two phases, with the downstream barrel completed between 1912-15 and the upstream barrel after 1925.

The siphon has undergone extensive repairs 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.