Hydrodynamic Characteristics of Critical Walleye and Lake Sturgeon Spawning Habitat below a Hydroelectric Dam in the Rainy River, Ontario

River regulation for the purposes of flood control and hydropower generation causes major deviations in the flow regime and resulting river hydraulics.  Success and stability of river ecosystems are often dependent on specific hydraulic conditions occurring on certain spatial and temporal scales.  During April – July of 2012 and 2013, Walleye and Lake Sturgeon spawning surveys were completed in parallel with spatial and temporal velocity profile sampling using Acoustic Doppler Current Profiler (ADCP) technology on a 21 km reach of the Rainy River below the International Falls Dam in northwestern Ontario/northern Minnesota.  83 hydrodynamic metrics were computed from ADCP velocity profiles obtained at 7 – 10 discrete discharges over the range in seasonal flows (100 – 900 m³/s), at 47 cross section locations.  Metrics did not trend significantly with discharge.  Cross sections were categorized according to spawning utilization (high, moderate, low).  Statistical analysis isolated metrics which demonstrated significant differences in temporal means and variances between locations of high, moderate, and low spawning utilization and highlighted the importance of spatial habitat heterogeneity in multi-attribute spawning site selection by Walleye and Lake Sturgeon.  The identified eco-hydraulic linkages will be applied to optimize spawning/nursery habitat for these species on the Rainy River.