Emergency Siphon Replacement Restores Flow to Montana’s Hi-Line

Northwest Pipe Company supplies 6,500 LF of 90-inch engineered steel pipe for the Milk River Project’s dual-line St. Mary Canal Siphon in Babb, MT

The St. Mary Canal is part of the Milk River Project, a 100-year-old transboundary water diversion system that originates at the St. Mary River on the Blackfeet Reservation near Glacier National Park. The 29-mile canal system passes through southern Alberta, Canada, before flowing back into north-central Montana, where it supplies water to 120,000 acres of farmland and 18,000 municipal users along the Milk River Basin.

In June 2024, the St. Mary Canal siphon breached outside of Babb, Montana. This catastrophic failure caused severe localized flooding and erosion, forcing the system offline. The Milk River Joint Board of Control (MRJBC) coordinated with the Bureau of Reclamation, State of Montana, and the Blackfeet Tribe to lead an emergency effort to replace the critically damaged, century-old siphon infrastructure. Northwest Pipe Company was selected to supply approximately 6,500 feet of 90-inch diameter engineered steel pipe for the project. HDR served as the project engineer. The lead contractors were NW Construction for earthwork and pipeline installation, and Sletten Construction for bridge and structural concrete work. Pipe setting and welding were performed by Pro-Pipe Corporation.

The project scope included removal of the failed pipeline, reconstruction of the siphon’s bridge crossing, and installation of the new 90-inch dual-line siphon system. Early site work included demolition of the original bridge and construction of a temporary structure to maintain access. NW Construction excavated the site and established a bypass channel to keep water flowing during installation, while also setting up a dewatering system to support winter work.

Manufactured at Northwest Pipe Company’s plant in Portland, Oregon, the C200 spiralweld steel pipe includes polyurethane coating and lining. Exposed segments of the pipeline—including portions for the bridge crossing—are top coated with Tnemec Endura Shield 1095. NWP also custom-fabricated elbows and outlet fittings for the system. The system connects using standard bell and spigot lap-welded joints.

Originally, a Carnegie-style joint and harness system was specified for the connections where the pipeline penetrates the concrete walls of the siphon’s inlet and outlet structures. Recognizing a simpler and more cost-effective solution to accommodate potential settlement at these points in the system, Northwest Pipe proposed a value engineering alternative, the InfraShield® Joint System. InfraShield® uses a patented strain-based design to enhance the resiliency of lap-welded steel pipe without the need for gasketed joints. This change was accepted into the project design and helped save installation time and costs at these critical points in the system. The four InfraShield® spools were fabricated at Northwest Pipe’s Adelanto, California facility.

“The St. Mary Siphon failure was an emergency no one wanted, but Northwest Pipe Company stepped up without hesitation. Their rapid response, high-quality product, and commitment to meeting our aggressive timeline were key in our decision to select them—and were instrumental in getting water flowing again to the thousands of farmers, communities, and ecosystems that rely on the Milk River. We’re incredibly grateful for their partnership.”

— Jennifer Patrick – Project Manager, Milk River Joint Board of Control

Coordination was key to staying ahead of the emergency project timeline. Northwest Pipe worked closely with NW Construction and MRJBC to align pipe production and delivery with on-site progress, ensuring construction remained on schedule. To continue installation through Montana’s harsh winter, insulated welding shelters were constructed in the trench, allowing field crews from Pro-Pipe Corporation to safely and consistently weld the pipeline through snow, ice, and freezing temperatures.

By late June 2025—just one year after the catastrophic failure—water was flowing again through the restored siphon. The project reestablished a vital water supply lifeline for municipal users, agricultural operations, and tribal communities across north-central Montana. Without the diversion system, the Milk River would typically run dry six out of every ten years. The rapid response and coordination by project stakeholders and field crews—alongside Northwest Pipe Company’s responsive manufacturing, design support, and delivery of durable steel pipe—made it possible to complete this urgent project ahead of schedule and secure the region’s long-term water supply.

For more information, visit: milkriverproject.com