St. Mary Facilities Drop Structures Emergency Repairs

St. Mary Facilities Drop Structures Emergency Repairs

St. Mary Facilities Drop Structures Emergency Repairs

Repairing the Water Supply Lifeline of Montana’s Hi-Line Region

The St. Mary Canal discharges to the North Fork of the Milk River after passing over the Hudson Bay - Gulf of Mexico Divide, within a few miles of the United States/Canada Border. The St. Mary Facilities are often referred to as “the lifeline of the Hi-line.” The system, which consists of a diversion dam and headgate on the St. Mary River, 29 miles of canal, two sets of steel siphons (74 to 90 inches in diameter) and five concrete drop structures, provides the critical trans-basin diversion of water from the St. Mary River Basin to the Milk River Basin. The system is located entirely on the Blackfeet Reservation in Glacier County, Montana.

The economy of the Hi-Line region in northern Montana is inextricably dependent upon the stable water supply provided by the St. Mary Facilities. The system provides water to irrigate over 110,000 authorized acres on approximately 660 farms within the Milk River Project area with a total of about 140,000 acres irrigated from the Milk River below Fresno Dam. The system also provides water for the Fort Belknap Indian Irrigation Project and municipal water to approximately 14,000 residents in the communities of Havre, Chinook and Harlem. In an irrigation season (May through September), approximately 70% to 95% of Milk River flow near Havre originates from the St. Mary River Basin. Beneficiaries of the St. Mary Facilities also include fisheries, recreation, tourism, water quality and wildlife. Rehabilitation of the system will also address critical habitat issues associated with species listed as threatened or endangered under the Endangered Species Act.

On or about May 16, 2020, a drop structure (Drop 5) experienced a catastrophic failure resulting in the inability to deliver water from the St. Mary Facilities. This would effectively eliminate approximately 10% of Montana’s irrigated agricultural economy, devastate Hi-Line communities and likely have economic repercussions across the state. Failure of the canal, siphons or drop structures would also likely result in substantial environmental damage on the Blackfeet Reservation in southern Alberta. In addition, failure of the system would jeopardize the Fort Belknap and Blackfeet Federal Reserved Water Rights Compacts.

The Milk River Joint Board of Control moved quickly to hire a contractor and HDR to proceed with replacement and repairs. We conducted emergency site visits and are now providing geotechnical, design and on-site support for the contractor while the team is moving forward with construction to re-establish water flow in the St. Mary Canal as soon as possible. In addition, while the canal is off-line, the team is moving forward with replacement of the structure at Drop 2, and working with the Bureau of Reclamation to perform maintenance and repairs on the other drop structures.

St. Mary Facilities Drop Structures Emergency Repairs
Client
Milk River Joint Board of Control
Location

MT
United States