Missouri Basin and Arkansas-Rio Grande-Texas Gulf Regions

St. Mary Siphon Updates

Overview

The Milk River Project (Project) was authorized by the Secretary of the Interior on March 14, 1903 and provides water to 110,000 acres of cropland and is a source of potable water for several communities. The Project provides irrigation water for approximately 110,000 acres on eight irrigation districts, about 110 individual Project pumpers, the Fort Belknap Indian Reservation, communities along the Milk River, and the Bowdoin National Wildlife Refuge.

St. Mary canal is the primary water supply for the Milk River Project, conveying 600 cfs from St. Mary River to Milk River from April through October. 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 reached the end of it's functional life-span on June 17, 2024 and will be replaced and this webpage will provide updates about the progress of the replacement over the next year.

The St. Mary Diversion Dam and Canal were completed in 1915 as part of the Milk River Project in north-central Montana. The dam is located near Babb, Montana and approximately 0.75 miles downstream from Lower St. Mary Lake.

Current Status

NW Construction, Inc. out of Bozeman, MT began removal of the siphon during the week of July 22 and has removed all of the west-side pipe. The east-side pipe removal started August 5. Once existing siphon material is removed, the excavation status will focus upon design grade.

Sletten Construction began driving piles on August 6, 2024 for the temporary work bridge. The demolition of the exisiting bridge is anticipated to begin on August 19, 2024. The permitting for the in-river work is complete with the Environmental Assessment and Finding of No Significant Impact signed on July 31, 2024 and the Biological Opinion was submitted to Reclamation by the U.S. Fish and Wildlife Service on August 2, 2024.

Operations

2024 Water Supply

• Fresno releases reduced to 100 cfs on July 31
• Carryover target of 17,000 Acre-Feet (AF) by Sept. 30
• Releases for municipal use will continue through the winter

2025 Water Supply

• Based on projected storage and median inflows irrigation would start in mid-May and peak at 800 cfs
• Irrigation releases would begin ramping down in mid-June to target 15,000 AF for municipal use
• Natural flow and Ft. Belknap Indian Irrigation Project storage right would be released until depleted.

Schedule

Completed Tasks

• Project Start: June 17, 2024
• Qualified EXM Determination: July 3, 2024
• Site Rehab Mod Contract: July 15, 2025
• FONSI: July 31, 2024
• Biological Opinion: August 2, 2024

Upcoming Milestones

• Bridge Removal: September 6, 2024
• Excavation to Grade: September 13, 2024
• Pipe Delivery: October 7, 2024
• Bridge Complete: December 1, 2024
• Inlet/Outlet Construction: June 2025
• Project Completion: September 2025

Costs

Estimated cost of $70 million to replace both St. Mary ($51.6M) and Halls Coulee ($18.4M) Siphons

Current available funding: $16,700,000

• Reclamation: $7,500,000
• Joint Board: $9,200,000

Task based project budget summary is avaiable on request

• Total Baseline Project Estimate = $70,000,000
• Total Project Spent = $5,300,000
• % Spent = 7.5%

Multimedia

Milk River Joint Board of Control Photo Gallery

Point of Contact

Steve Darlinton

Project Manager
(406) 247-7322
sdarlinton@usbr.gov
Bureau of Reclamation
Montana Area Office
P.O. Box 30137
Billings, MT 59101
(406) 247-7300