High-resolution hydrodynamic modelling to study year-round circulations and inter-basin exchanges in Lake Winnipeg

Abstract A new high-resolution (500 × 500 m), three-dimensional hydrodynamic model was applied to Lake Winnipeg to study summer and winter water circulation, temperature, and ice-cover during 2016–17. The model was run with a combination of buoy-based observations and the outputs from the Global Environmental Multiscale model forcing. Four primary riverine inflows and two outflows were considered in the model. The bathymetry from a previous study by the authors was revised using a 2018 survey covering the South Basin and the Narrows. Comparisons of this new model with the previous model setup (2 km resolution) show noticeable improvements in all simulated parameters. In the Narrows, where seiche-driven flows have predominant oscillation periods of ~27 h and ~17 h, the RMSE of simulated currents is 0.1 m s−1, half of that of the previous simulations. The new model was able to reasonably simulate the spatial development of ice-cover over the lake. The ice-free period circulation results show that there are two clockwise and counterclockwise gyres in the North Basin, and a weak seasonal clockwise gyre in the South Basin. Monthly circulation patterns differ from those during short wind events due to spatiotemporal variability of wind patterns. The materials from the Red and the Winnipeg Rivers need ~50 days to reach the Narrows before transported from the South Basin to the North Basin. The daily inter-basin exchange flow oscillations during the ice-free period can range up to ~3.5 × 104 m3 s−1, while under-ice daily exchanges are always northwards with values depending on inflowing riverine discharge up to ~0.5 × 104 m3 s−1.