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Analyzing the St. Marys Rapids for Suitable Fish Habitat: An Engineering with Nature Demonstration(Registered) Project


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The St. Marys rapids at the outlet of Lake Superior is a vital habitat for a wide range of aquatic species. The regulation of the outflows from Lake Superior by Compensating Works (i.e., a series of control structures) can lead to rapid changes in hydraulic characteristics, potentially creating adverse conditions for downstream biota. To accomplish more naturally varying flows, the U.S. Army Corps of Engineers (USACE) Detroit District (LRE) is constructing four remotely operated gates on the United States (U.S.) side of the Compensating Works. The gates will be capable of being opened slowly (over many hours) until a desired discharge is achieved. A two-dimensional (2-D) model was developed to evaluate multiple scenarios and analyze the total area available for fish spawning based on depth and velocity associated with a particular gate setting. The model also addressed the recommendation for water level rates of change associated with gate changes, suggesting that water level rates of change be held to less than ten centimeters (cm)/hour to avoid stranding juvenile fish. This is consistent with Engineering With Nature(Registered) (EWN) principles of maximizing habitat value of the rapids while maintaining water regulation objectives.



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