Bathymetry Estimation Using Drifter-Based Velocity Measurements on the Kootenai River, Idaho

Velocity measurements from drifter GPS records are used in an ensemble-based data assimilation technique to extract the river bathymetry. The method is tested on a deep meandering reach and a shallow braided reach of the Kootenai River in Idaho. The Regional Ocean Modeling System (ROMS) is used to model numerous statistically varied bathymetries to create an ensemble of hydrodynamic states. These states, the drifter observations, and the uncertainty of each are combined to form a cost function that is minimized to produce an estimated velocity field and bathymetry. The goals of this study are to assess whether ROMS can accurately reproduce the Kootenai River flow to an extent that depth estimation is feasible, to investigate if drifter paths are sensitive enough to bottom topography to make depth estimation possible, and to establish practical limitations of the present methodology. At both test sites, the depth estimation method produced a bathymetry that was more accurate than the prior estimate.