Alberta Agriculture and Irrigation (AGI) needed a reliable, science-based tool to manage releases from the St. Mary Reservoir in a way that protects downstream cold-water fish habitat while continuing to meet irrigation and other water-use demands. During summer low-flow conditions, elevated water temperatures in the lower St. Mary River can stress cold-water species, creating a management challenge that requires an ability to predict how release frequencies and rates affect downstream temperatures. AGI retained Barr to develop a calibrated temperature model for a 100-kilometre river reach downstream of the reservoir.
We started by monitoring river temperature, dissolved oxygen, and water level during ice-free conditions for three years. We also collected river flow measurements and channel bathymetry along the river. These data were combined with AGI's monitoring data to create a robust data foundation for model development. Using these data, we developed and calibrated a one-dimensional hydraulic and temperature model in HEC-RAS to simulate how river temperatures respond to changes in reservoir releases during ice-free conditions.
The model allows AGI to test “what if” scenarios—such as adjusting release rates during warm periods—and evaluate potential downstream temperature effects before implementing operational changes. By tailoring our modelling approach to site conditions and monitoring data, and by clearly documenting model assumptions and limitations, Barr built a reliable predictive tool that informs reservoir operations and helps AGI balance ecological protection with operational requirements.
