Pipe replacement delivered for St. Mary Siphon

Staff and wire report

U.S. Bureau of Reclamation announced last week that the the first sections of the 90-inch replacement pipe for the St. Mary Siphon had arrived, marking a major milestone of the extensive project to restore the damaged siphon. This milestone sets the stage for replacing the critical infrastructure that delivers water to the Milk River Project, a lifeline for north-central Montana ranchers, farmers, and communities.

"This delivery of the replacement pipe is an important step in restoring a critical piece of Montana's water infrastructure," said Ryan Newman, Reclamation's Montana Area Office manager. "The St. Mary Siphon plays a vital role in delivering much-needed water to the Milk River Project. By beginning the process of full replacement, we are ensuring the continued viability of the region's agriculture and the livelihood of thousands of Montanans."

The more-than-100-year-old system, that provides much of the water in the Milk River each year, has been band-aided together for decades. As an irrigation project - the Milk River Project and the St. Mary Diversion and Conveyance works were one of the first projects the Bureau of Reclamation was authorized to build after it was created in 1902 - originally, the irrigators in the Milk River Project were required to fully fund the operation and maintenance of the system.

In the last 20 years, the federal government has picked up some of the funding, but the majority still comes from the irrigators.

For the last 25 years or more, the irrigators have pushed for rehabilitation of the system, urging work before catastrophic failure.

The June 17 failure of the siphons, an integral part of the 29-mile-long conveyance works that transport water diverted from the St. Mary River into the North Fork of the Milk River, was the second castastrophic failure this decade. In 2020l, a concrete drop structure collapsed, shutting down the diversion and leading to intense collaboration and effort to get it repaired by that fall.

The St. Mary Siphon is an essential component of the Milk River Project, one of Montana's most significant irrigation systems, which serves over 120,000 acres of farmland. For the agricultural community and surrounding residents, the siphon's repair is crucial to maintaining water supplies necessary for crops, livestock, and daily living.

The siphon failure June 17 required 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% to 80% 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 consisted 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. 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. The funding came from the Bipartisan Infrastructure Act signed into law by President Joe Biden in 2021.

For more information on the St. Mary Siphon replacement project, please visit St. Maryon Updates at https://www.usbr.gov/gp/mtao/stmary_siphon .