Development and Calibration of Two-Dimensional Hydrodynamic Model of the Tanana River near Tok, Alaska

Abstract

Abstract : This report presents the methods used, data collected, and hydrodynamic model results from the USGS and ADOT&PF study to collect bathymetric and topographic data for a hydrodynamic model of the Tanana River where bridge 505 of the Alaska Highway makes its crossing. The USGS collected an extensive bathymetric and hydraulic data set in the vicinity of the bridge using ADCP, RTK-GPS, and an echo sounder. These data, along with survey data of the overbanks collected by ADOT&PF were used to construct a two-dimensional hydrodynamic model in the vicinity of the bridge. A calibration discharge of 25,600 cubic feet per second was simulated with the U.S. Geological Survey's Multi-Dimensional Surface Water Modeling System. This model is a generic interface that currently uses a two-dimensional, vertically averaged steady-state flow model with curvilinear orthogonal or simple rectilinear grid. Boundary conditions and model parameters were calibrated to data collected during the hydraulic survey. The drag coefficient for the channel was calibrated through an iterative process where predicted water-surface elevations and flow velocity magnitudes were compared to measured values. The lateral eddy viscosity was also calibrated though an iterative process and predicted velocity vectors compared to those measured by the ADCP. A model of the 100-year recurrence interval discharge was constructed using calibrated parameters from the simulation of the measured discharge and a starting water-surface elevation calculated with a one-dimensional model. Predicted flow angle of attacks increased from 38 to 45 degrees and 45 to 55 degrees on the left- and right-bank piers, respectively. A second simulation of this discharge was run with the existing piers removed from the channel. Predicted velocities, water-surface elevations, and velocity vectors from these simulations will aid ADOT&PF in the design of a new bridge in the event that the existing bridge is removed from the channel.