A project designed to help improve the data needed to properly share water between Canada and the United States in the St. Mary and Milk River basins has completed its first step, paving the way for field work over the next year.
Under the 1909 Boundary Waters Treaty and a subsequent 1921 Order from the IJC, the United States and Canada must equitably share the water that flows between the rivers equitably to ensure communities and the agricultural sector have the water they need.
A canal connecting the two rivers helps move water from the St. Mary River – which flows north from the Rocky Mountains in Montana into Alberta – into the Milk River, which flows eastward from Montana into Alberta before reentering Montana. Since the Milk River’s natural flows can get quite low in the summer months, water from the canal is used to bolster the amount available for agricultural users who need to irrigate their land.
Natural flows and water needed and used by irrigators are estimated by the IJC’s Accredited Officers of the St. Mary-Milk Rivers, who are appointed by the two countries’ governments. Ensuring these estimates are as accurate as possible is an ongoing interest to the officers.
As such, in 2018 the IJC funded a study through its International Watersheds Initiative to use a remote-sensing method developed by a team of US Geological Survey (USGS) scientists at the USGS Earth Resources Observation Science Center and called the Operational Simplified Surface Energy Balance. By using satellite imagery, coupled with visits on the ground, the team will be able to better pinpoint the amount of water the existing crops and irrigators need.
The key to this project are Landsat satellites that the United States has been launching into orbit since the early 1980s. Thanks to the data collected by these satellites, the team working on the project with the USGS has assembled data from 1985 through 2020, said Roy Sando, remote sensing and GIS specialist with the USGS Wyoming-Montana Water Science Center.
“Basically, we can use satellite imagery to determine how much water plants are using,” Sando said. “Since Landsat has global coverage, we’re getting around the need for individual countries to do their own reporting and then us trying to merge that information.”
This first of three phases, completed this fall, involved the team putting together annual estimates on the amount of water crops use in the St. Mary and Milk River basins using those 35 years of data to prove that this project is broadly feasible.
The collapse of the St. Mary Canal in May changed the workload for 2020, as the project team prioritized the collection of Canadian water use data. Since the canal was no longer capable of supplying additional water to the Milk River, it was possible to gather information on how water usage and irrigation patterns in Canada changed when the river was reduced to its natural summer flows. The canal was repaired and operational again by October 14, when a ribbon-cutting ceremony was held and flows into the river resumed.
The project’s second phase is due to start by year’s end and will see team members visiting spots on both sides of the border to inventory all of the irrigated fields in the basin. They’ll catalog what crops are grown there, what kind of irrigation is used, what type of soil the plants are growing in and sync the surveys with information from the satellites.
The third and final phase will assemble the information into an online tool that irrigators and water managers can use to help with apportionment, describe how apportionment decisions are reached, and see how different climate and water conditions can impact how water is used in the region.
This process should prove to be more accurate than older methods of measuring the water use. These older methods rely on a “crop coefficient,” Sando said, that essentially sees the accredited officers determining a single value of water used based on a whole field of crops. The new approach would allow them to get water usage values on a smaller scale, closer to real time – roughly in 100-meter blocks across the entire basin.
This project is designed primarily to account for the growing season in the St. Mary-Milk system, Sando added, as there is little irrigation outside of the May-October period in the basin.
Besides the unexpected collapse of the canal in May, there have been other challenges to this project. The COVID-19 pandemic has closed the border between Montana and Alberta for months, which may force the work to be done by separate teams in either country. Joanna Thamke, associate center director at the Wyoming-Montana Water Science Center and field representative of US Accredited Officer John Kilpatrick, noted that ground surveys are usually done by two-person teams: a driver and a mapper using a tablet. . Due to the pandemic, Thamke said it’s more likely that one person will do both jobs by mounting the tablet on the dashboard and stopping periodically to input data.
Additionally, satellite imagery can be obscured by cloudy or smoky conditions, Sando said, requiring statistical modeling to fill in the subsequent gaps this can cause. Finally, Canadian datasets have required a different methodology to be properly plugged into the USGS Operational Simplified Surface Energy Balance, which is still underway. Notwithstanding these challenges, the remote sensing project and online tools are tentatively expected to be completed by 2024.
The remote sensing project is led by USGS, but it has support and participation from several other agencies and organizations: Montana Department of Natural Resources and Conservation, Alberta Environment and Parks, Water Survey Canada and Water Security Agency Saskatchewan.
Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.