Improvement of a Three-Dimensional Hydrodynamic Model Downstream of a Lock and Dam Using ADCP-Derived Bathymetry and Velocity Field Observations

Abstract

Locks and dams alter downstream hydraulics by changing channel geometry, flow distribution, and velocity structure. This study improved an EFDC+ three-dimensional hydrodynamic model downstream of Claiborne Lock and Dam on the Alabama River using updated bathymetry and parameter adjustments. Boundary conditions were based on USGS discharge and water-level data, while 2018 U.S. Army Corps of Engineers bathymetry provided the baseline geometry. ADCP surveys conducted in September 2025 supplied updated bathymetry and observed velocity magnitude along five downstream transects. Model performance was evaluated using RMSE and PBIAS through sequential adjustments to bathymetry, bottom roughness height, and weir discharge coefficient. The 2025 bathymetry produced the greatest improvement, reducing average RMSE from approximately 0.20 to 0.12 m/s. A roughness height of 0.045 m provided the most balanced velocity representation, whereas increasing the weir discharge coefficient from 0.65 to 0.95 produced smaller, localized effects.