New Study Maps the Bed of the Rainy River

A recently completed study supported by the International Rainy-Lake of the Woods Watershed Board’s Adaptive Management Committee has mapped the bed of the Rainy River from Manitou Rapids to the mouth of Lake of the Woods.  

Coupled with an earlier study that had mapped the riverbed from International Falls, Minnesota to the Manitou Rapids, researchers have now scanned the entire length of the river’s underlying geography, said Zac Morris, engineer with AMI Consulting Engineers, which was contracted for this project.  

Manitou Rapids was the starting point. “Everything preceding the Manitou Rapids had good data, and everything below it was spotty. So about 48 river miles or 77 kilometers of survey was required.” 

The survey was carried out by AMI staff in July and August 2024, Morris said, covering that stretch of the river in several passes using multi-beam sonar systems. AMI collaborated closely with the Canada Hydrographic Society to prepare for the survey. The entire bottom of the river needed to be finely mapped, he explained, which required this extensive effort.  

This data is now being processed by Environment and Climate Change Canada, said Marianne Bachand, a project coordinator in ecohydraulic modeling working on the study. Bachand said that this new survey data will be combined with existing topographic data to create a Digital Elevation Model (DEM) for the entire river. A DEM is a three-dimensional representation of the surface, excluding trees, buildings and other objects. 

This DEM will, in turn, be useful for developing other models valuable to the Adaptive Management Committee, as well as for water managers and anglers, Bachand said. 

“We’ll calibrate a hydrodynamic model,” Bachand said. “That will allow us to predict the water level locally everywhere in the river [under different conditions]. We’re expecting that by next fall, and once that’s finished, we’ll improve our habitat modeling for lake sturgeon and walleye in the river as well.” 

These models will all be used for the regular evaluation of the existing rule curves, said Bachand, which are used by water managers and the International Joint Commission (IJC) to target water levels throughout the year for the basin. In this way, decision-makers can ensure that future rule curves take these ecological needs into account with a fuller picture of how water can move through the river system. 

The DEM and the hydrodynamic model are components of an Integrated Socio-Economic and Environmental (ISEE) system for the river system, Morris said. The IJC has used ISEE systems in its work in other basins, such as Lake Champlain and Lake Ontario and the St. Lawrence River, to determine the environmental and economic impacts of varying water levels, including extreme events. Bachand said the ISEE system could be useful for fleshing out other potential indicators for the rule curves and their effectiveness, including identifying risks to development in floodplain areas or to culturally sensitive sites for Indigenous communities in the basin. 

The DEM should be completed by the end of the summer, Bachand said, with the other models stemming from it coming down the line.