This paper describes the results of numerical modelling of wave disturbance in the harbor of Ronne, Denmark, using the hydrodynamic modelling System 21 of the Danish Hydraulic Institute. The name of the system indicates that it can be applied to unsteady 2-dimensional flow in 1 layer. It includes the so-called “Boussinesq” terms, which account for the deviation from hydrostatic pressure distribution caused by the vertical accelerations. It can simulate the phenomena of diffraction, refraction, reflection, and shoaling of natural irregular waves in a harbor of arbitrary shape and bathymetry. Comparisons have been made between the disturbance coefficients of numerical modelling and those of physical modelling and also between the former and those of field measuring data. The results indicate that there is in general a good agreement between them. This paper describes the results of numerical modeling of wave disturbance in the harbor of Ronne, Denmark, using the hydrodynamic modeling system 21 of the Danish Hydraulic Institute. The name of the system that that can be applied to unsteady 2-dimensional flow in 1 It includes the so-called “Boussinesq” terms, which account for the deviation from hydrostatic pressure distribution caused by the vertical accelerations. It can simulate the phenomena of diffraction, refraction, reflection, and shoaling of natural irregular waves in a harbor of arbitrary shape and bathymetry. Comparisons have been made between the disturbance coefficients of numerical modeling and those of physical modeling and also between the former and those of field measuring data. The results indicate that there is in general a good agreement between them.