Comparison of results from two 3D hydrodynamic models with field data : internal seiches and horizontal currents

Abstract

Model skills of two 3D hydrodynamic models, ELCOM and Delft3D, were assessed by simulating internal seiches and surface currents and comparing the results with field data in Upper Lake Constance, Germany. Both models were set up using the same horizontal and vertical discretisation and forced by a horizontally resolved wind field. Model simulations were carried out during a stable stratification period in summer. Oscillations of the simulated and the measured isotherms in Lake Überlingen (north basin of Upper Lake Constance) indicated the existence of a Kelvin-type wave with a period of 84 h. The major wave pattern in period and amplitude was consistent between the simulations and the measurements, whereas discrepancies appeared in the phase match. The measured and the simulated vertical velocity structure in the middle of the main basin of Upper Lake Constance showed occurrence of a Poincaré-type wave with a 14 h period. Major oscillations of the velocity structure were captured by both models, and the agreement between the simulations and the measurements was higher in deep layers than in near-surface layers. Model prediction of the near-surface velocities as well as the surface circulation pattern was more accurate under high current velocities during strong winds than under weak winds. This study concluded that both ELCOM and Delft3D were significantly skilled at simulating internal wave motions and surface currents, and there was no significant difference in reproducing the measured lake dynamics between ELCOM and Delft3D.