River Analyzer: A New Three-Dimensional Hydro-Acoustic River Mapping Tool to Estimate Drift Rates for Larval Pallid Sturgeon over Distances of 100's of Kilometers

Previous estimates of larval pallid sturgeon drift rates in Montana’s Missouri River below Fort Peck Dam were calculated using 1-dimensional HEC RAS model results, indicating that most larvae drift into Sakakawea Reservoir (~375 river km) in just six days, providing insufficient river residence time for survival.  Previous larval drift experiments used to calibrate the drift model focused on the bulk of the drifting larvae.  Hence, questions remain about the slowest drifters that have the greatest potential to residualize in suitable habitat and survive.  We mapped spatially dense 3D river hydraulics using an array of multi-beam Acoustic Doppler Profilers and GPS.  New software called, “River Analyzer”, integrates bathymetry, velocity and current vectors in 10 cm vertical increments, enabling calculation of drift speed and migration pathways throughout 337 km of the Missouri River.  Results revealed complex bathymetry (to 10 m depth), braided flow channels, and velocity fields from 0 to 2.5 m/s. Equally complex larval drift paths indicated where larvae are swept from the thalweg into low velocity habitats, further extending river residence time for the slowest moving larvae.  We emphasize the long distances mapped by River Analyzer, the need to understand complex drift patterns, and recommend applications to optimize dam operation.