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Montana Ag Network: Repairs to St. Mary canal drop structures to start soon

Posted at 6:11 AM, Jun 18, 2020

The Milk River is the lifeline for Montana’s Hi-Line, providing irrigation water to 110,000 acres and drinking water for many communities, including Havre, Chinook, Harlem, and Malta.

But on May 17 a concrete drop structure failed on the St. Mary Canal northwest of Cut Bank putting these Hi-Line producers and residents in jeopardy of losing their water.

The good news for Hi-Line residents is the Milk River Joint Board of Control, U.S. Bureau of Reclamation, and Montana DNRC have agreed to begin replacement of the failed Drop 5 structure on the St. Mary’s Diversion. Another drop structure, Drop 2, is considered at risk for failure and will also be replaced.

Jennifer Patrick is the Milk River Joint Board of Control’s Project Manager and says these repairs will help to ensure the Milk River will continue to serve Montana’s Hi-Line with water.

“I would love to say we are going to add to the irrigation season, but essentially we're looking at next year and that storage and that carry over,” said Patrick. “If we have the opportunity to move water at the end of the season and get it across, we're just in a better spot in in Fresno starting the year next year.”

They’re very thankful for Montana’s Congressional delegation which continues to fight for funding to repair the entire structure which is over 100 years old.

“Senator Tester, Senator Daines and Congressman Gianforte have been there saying we need this, but it's been falling on deaf ears,” said Patrick. “I think people are seeing that now with the failure as we're sitting here saying, you know, cities and towns might be out of water and, you know, all of these all of these other factors that factor into it that have become a beneficial use.”

She says the Milk River truly is the lifeline of Montana’s Hi-Line. “Agriculture forms the underpinning of this economy here,” said Patrick. “And without this water source, we're in a bad spot.”

Together, HDR Engineering and Sletten Construction Companies will be carrying out the replacement with repairs set to begin June 22.

The majority of construction of the Milk River Project was completed between 1906 and 1940. The canal was constructed between 1907 and 1915 and is the primary water source for eight irrigation districts tribes, contract pumpers, and several municipalities downstream of Havre serving approximately 110,000 acres of land.

The agency website provides the following information:

  • The St. Mary's Diversion Dam, located on the St. Mary River 0.75 downstream from Lower St. Mary Lake, is a 6-foot-high concrete weir and sluiceway with a length of 198 feet and a total volume of 1,200 cubic yards. The St. Mary Canal begins at the St. Mary Diversion Dam on the west side of St. Mary River and crosses the river 9.5 miles below the diversion through a two-barrel steel-plate siphon 90 inches in diameter and 3,600 feet in length. Eight miles below the St. Mary crossing a second two-barrel steel-plate siphon, 78 inches in diameter and 1,405 feet long, conveys the water across Hall's Coulee. A series of five large concrete drops at the lower end of the 29-mile canal provide a total fall of 214 feet to the point where the water is discharged into North Fork Milk River. Design capacity of the canal is 850 cubic feet per second.