The Milk River runs the risk of running dry later this summer, which would eliminate irrigation for 40 southern Alberta water licence holders, change cattle pasture rotation for ranchers, force municipal water restrictions and damage the river’s aquatic ecosystem.
No water will be transferred from the St. Mary Basin into the Milk River Basin this year due to failure of a drop structure on the Montana side in May and the state’s plans to halt diversion in order to make repairs over the summer.
The Milk River is usually able to maintain flow levels by virtue of water diversion from the St. Mary River through structures located in Montana. Though recent rainfall in southern Alberta alleviated some of the pressure, Alberta Environment estimates flow by the end of June could be at or below one cubic metre per second. When the diversion failed last month, river flow was 20 cubic metres per second. As of June 15, it was three cubic metres per second.
“We’re pretty close to the tipping point right now, where licensed water diversion amounts, as everybody wants to be using their full diversion capacity right now, that we would have no water left in the river,” said Tim Romanow, executive director of the Milk River Watershed Council.
Thus the irrigation season is already near an end for the 40 families who irrigate from the Milk. Some ranchers also use the river as a virtual fence, said Romanow, so they are altering their cattle pasturing plans.
Affected municipalities have already implemented voluntary water-use restrictions. Romanow said the town of Milk River and village of Coutts have a three-month supply of water without needing to pump from the river. That should carry them through the dry season unless the weather turns droughty and provided there are no major fire suppression needs.
“Right now, it’s entirely up to Mother Nature to give us whatever water we’re going to get,” said Romanow.
The Milk River has run dry before. In 2001, a rupture occurred in the aged siphon system in Montana, shutting off the diversion for about 10 days. The eastern end of the Milk ceased to flow, leaving only a few puddles to support aquatic life.
Kevin Reese, who irrigates his crops from the Milk River near Writing-On-Stone Provincial Park, was still running his pivot June 15.
“We’re hoping that we’ve got water to the end of June,” he said, although that remains to be seen. Reese grows cereals and seed canola, and also irrigates some pasture.
“It’s our cash crop,” he said about the canola, “so it’s not looking great for it because it needs later season water.”
He has been in touch with other irrigators in the region.
“We’re all concerned but we realize there’s not much to be done. On the one hand we’re wishing that they could keep the water flowing but we understand and glad that they’re fixing it properly so that we don’t have to worry for next year.”
The Milk River Joint Board of Control, an international body, decided against any temporary remedies in favour of permanently fixing the failed drop structure as well as one other structure considered to be at high risk of failure.
“There is a possibility that the St. Mary canal will be operable by September 2020,” Romanow said in an email to water users. “If this is the case, the plan would be to transfer water stored in Lake Sherburne to the Milk River Basin during September and early October.”
A release from the U.S. Bureau of Reclamation said the damaged drop structure is located northwest of Cutbank, Montana, on the Blackfeet Indian reservation. It is one of five that convey water through the 46-kilometre-long St. Mary canal to the north fork of the Milk River.
Members of the joint board “concluded that the complexities and costs associated with providing an interim solution to run water this irrigation season could not be justified considering the anticipated costs and minimal gains in water supply.”
Romanow said backup plans in Canada are being discussed in case the river does go dry and water supplies become dire. They include a temporary above-ground pipeline that would carry water from Ridge Reservoir south of Raymond, Alta., to Milk River.
Also a worry is the health of aquatic life in the river, which is home to three endangered fish species:
Rocky Mountain sculpin, stonecat and Western silvery minnow.
Romanow said the watershed council plans to document the effects of low water flow on the economy and environment. The data could be useful to support future plans for increased water storage in the watershed.