Combined Numerical and Physical Modelling of Seiching in Exposed New Marina

Abstract

This paper describes the modelling of seiching in an exposed new marina using the combination of numerical and physical modelling. The new Western Marina is part of the Beirut Central District reclamation scheme (Lebanon). Due to the rapidly changing shallow water bathymetry near the harbour entrance, hydraulic design studies paid particular attention to the potential for seiching in the new marina. Both models show that the long-period wave energy is concentrated around frequencies corresponding to wave periods of 50-80s (fundamental natural mode) and 67 minutes (Helmholtz mode). The non-linear Boussinesq type model is applied to understand the seiching phenomena, for calculation of the spatial variation of the long wave amplification, screening of alternative harbour configurations and to investigate possible model effects in the physical model. The physical model is interactively applied to investigate in detail the most promising layouts, especially for incident wave conditions associated with strong wave breaking, where the numerical model is not yet feasible. Comparison between physical and numerical model results is shown to be in excellent agreement supporting this strong approach in future studies of low frequency oscillations in ports and harbours forced by wind-waves and swell.