Collapse of an irrigation structure in northern Montana last week is affecting flow in the Milk River on the Alberta side, potentially disrupting the coming irrigation season.
The Milk River as it flows into Canada is dependent on a diversion of water from the St. Mary River into the Milk through a canal and siphon system. One of the concrete drop structures on that system failed on May 17, just before the U.S. Bureau of Reclamation had planned to shut off the water to do minor repairs before the irrigation season began in earnest.
Tim Romanow, executive director of the Milk River Watershed Council, said American officials are expected to assess the problem this week so it was a wait-and-see situation as of May 25. The failed structure is in a remote area northwest of Cutbank, Mont., so access, particularly after 60 millimetres of rain in the region, delayed immediate assessment. As well, the system has to be shut down, or “de-watered,” before a full check and repair plan can be made.
“Unfortunately, this is a 105-year old structure and it’s extremely remote. On the U.S. side, it is probably about a 25 kilometre trip from the nearest gravel road in order to get into it,” said Romanow.
“Calling it a road is being pretty generous because it’s basically a cart trail. One of the biggest challenges I think the U.S. Bureau of Reclamation is going to have is getting in to make the repair and having the materials on site.”
Some 8,200 acres are irrigated from the Milk River on the Canadian side, affecting about 40 families. About 20 percent of those acres are high-value specialty crops and the other 80 is split between grain or oilseeds and forage.
If the system is down for the entire 2020 irrigation season, those acres would be affected, particularly if there’s little rainfall.
“We did some corner of the napkin math … to kind of figure out what the potential impact would be,” said Romanow.
“If there was a total loss of the 2020 irrigation season, we’re probably looking at an impact of about $2.5 million directly to the producers. That doesn’t sound like a big number in the whole scheme of things, but when you’re talking 40 families, that’s a lot.”
The Town of Milk River and villages of Coutts, Alta., and Sweetgrass, Mont., also depend on the system for municipal water.
The impact is even larger on the Montana side, where 93,000 acres are at least partially affected by the problem. However, water reservoirs on the U.S. side are at or near capacity and recent rainfall has eased moisture stress at this point.
Natural flow in the Milk River is low without benefit of the diversion that’s been in place for more than a century, said Romanow.
The Milk is a foothills tributary that relies mostly on natural springs, not mountain runoff like most other Alberta rivers.
That means the Milk River could run dry during the peak summer months, or at best become a small creek. That threatens the riparian and aquatic health of the system as well as three species at risk that live in the river.
The Milk River is also considered one of the top 10 paddling destinations in Canada so recreation and tourism could potentially be affected if the repair cannot be made this year.
The USBR said it was assessing the damage on the drop structure in the aged system.
“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,” it said in a statement.
Albertans have long feared a failure of the system, but finances to upgrade it on the U.S. side, estimated to cost more than US$175 million, haven’t been available.
The fact that it has lasted this long without catastrophic fail is a tribute to the original engineers, said Romanow.
“It’s incredible infrastructure. They knew what they were doing back then. We’re talking about stuff that was built during the age of the Titanic. That puts it in perspective.”