Siphons break in St. Mary Diversion

A siphon on the more-than-100-year-old system that provides much - almost all, in drought years - to the Milk River broke last Monday, shutting down the system.

The Montana Area Office of the Bureau of Reclamation area manager said the bureau was waiting for the water to finish flowing out of the breached siphons on the St. Mary Diversion and Conveyance Works and is working to get a feel for impacts caused by the breach and looking at possible models for replacement or partial repair.

"We're currently in an analysis, data gathering stage and we're going to be in that posture for at least a week before we can plot some paths forward," Area Manager Ryan Newman said in an interview with Havre Weekly Chronicle.

He said a top priority right now is keeping people out of the area of the breech to maintain public safety.

"Our immediate response is to keep the public away and wait for the flow event to pass and the ground to dry up a little bit so we can actually get in there and start assessing our path forward," Newman said.

The system, part of the Milk River Project authorized at the start of the last century, provides water for more than 120,000 acres of irrigated cropland and municipal water for Havre, Chinook and Harlem, as well as recreation on the Milk River and reservoirs that are part of the project like Fresno Reservoir west of Havre and Nelson Reservoir northeast of Malta.

Nelson said Fresno Reservoir right now is near full, and the breach should not have an immediate impact on the towns that use the water or the irrigators.

He said the breach was discovered last Monday morning after BOR staff had already done an inspection and went back out and saw something didn't look right. One of the siphons - the system has two siphons - had burst, Newman said.

The water coming from the siphon softened the ground and caused erosion, leading to the second siphon also breaching.

He said the possible actions would be a full replacement of the siphon - adding that that would not be likely this summer - or partial replacement or taking no action this summer.

He said this will be shortened irrigation season, although the recent rains have reduced demand at this point.

A system in need of repairs

The St. Mary Diversion and Conveyance Works was one of the first projects BOR was authorized to build after it was created at the start of the last century.

Completed in 1915, the system takes water diverted from the St. Mary River by a diversion dam near Babb through a 29-mile series of siphons, canals and drop structures, mostly on the Blackfeet Indian Reservation, to the North Fork of the Milk River, which then flows into Canada before returning into Montana.

It provides 40 percent to 60 percent of the water flowing through the Milk River in most years, as much as 90 percent or more in drought years.

Before the diversion was built, by fall the Milk River dried up in 6 out of 10 years. Users have been warning for decades the system was close to collapse.

About 2000, users began warning of the chance of a catastrophic failure of the system.

Created as an irrigation system, all of the funding for the operation and maintenance of the Milk River Project came from users, primarily the irrigators. The system had been patched together for decades by 2000, and the irrigators said it was close to failure. The state created the St. Mary Rehabilitation Working Group, with the lieutenant governor an automatic co-chair of the group, to find ways to do that.

And the warnings came true. This is the second catastrophic failure to the system in less than five years, with it shut down in 2020 when one of the concrete drop structures near the end of the conveyance works collapsed.

The first of the repairs on the system, work on the diversion dam near Babb, funded through the infrastructure bill was awarded to a Montana company last week.

Newman said Tuesday that the work on the dam has nothing to do with the conveyance works and the siphons.