Like other parts of the Canadian Shield, water is omnipresent in the Mauricie region of Quebec. Numerous lakes, large and small, dot the surface—a byproduct of the glaciers that carved depressions into the region’s igneous bedrock during the most recent ice age.
However, people also played a role in shaping the region&rquo;s waterways when they created Réservoir Gouin, the sprawling many-armed lake shown in this satellite image. The scene was acquired by the OLI (Operational Land Imager) on Landsat 8 on October 17, 2023. Dark patches northwest of the reservoir are recent burned areas; brown and yellow areas to the east have been logged.
Construction of the Gouin dam began in 1916 to regulate the flow of the Saint-Maurice River and make it easier to float wood to pulp and paper mills downstream. After the concrete structure—measuring 26 meters (85 feet) high and 502 meters (1,647 feet) long—was finished, it transformed the network of lakes and river valleys upstream into what was then the world’s largest reservoir. It also meant that Obedjiwan (also spelled Opitciwan), an Atikamekw village on the north shore of the new reservoir, had to move to higher ground.
Before the dam’s construction, the flow of the Saint-Maurice River varied sharply from one season to the next. In 1913, for instance, it fluctuated between 170 cubic meters per second in the summer and 5,700 cubic meters per second during the spring flood, according to Hydro Québec.
The dam ultimately curtailed such swings, but the reservoir still sees seasonal variations. In winter, managers lower water levels to make room for spring snowmelt and summer rains, and they allow water levels to peak in the late summer or fall.
Such seasonal variations in the water level are observable from space. Gouin is among more than 300 lakes and reservoirs that NASA scientists monitor using data collected by radar altimeters on several satellites, including Jason-2, Jason-3, and Sentinel-6 Michael Freilich.
The project, based at NASA’s Goddard Space Flight Center, posts new water height measurements of the reservoir every two weeks. The reservoir’s water levels typically drop a few meters in the winter and have trended upward by a few meters overall since the 1990s, the satellite observations show.
NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.
