RefTide: The Reflection and Resonance Behaviour of Tide Dominated Estuaries

Tidal waves entering estuaries are amplified or attenuated due to processes resulting from cross-sectional convergence, friction, reflection and resonance. While there is a basic understanding of the processes of reflection and resonance of tidal waves, there is a knowledge gap in the quantification of the processes for tidal waves in estuaries and especially of the effects of multiple reflections. Within the KFKI-funded research project RefTide these gaps have been addressed with the aim to improve the system and process understanding of reflection and resonance in tide dominated estuaries. The Elbe estuary was chosen as the main study area. In RefTide a comprehensive analysis of the tidal dynamics of the Elbe estuary (and the influence of different factors on the tide generated oscillations) is carried out by combining advanced analytical and numerical models with empirical studies based on available time series of water level and flow data. In addition, methods for resonance analysis were developed and applied to the Elbe estuary.

The reflection behaviour of tidal waves was investigated model-based using a self-developed analytical model as well as on a large number of model tests with different hydrodynamic numerical models (principal models, Elbe estuary model).

The results of the investigations improve the knowledge on the formation of the tide generated oscillatory system and clarify the importance of reflection, resonance and dissipation of tidal waves in estuaries. In addition, the effects of various influencing factors on the oscillatory system were determined and described. Resonance is a consequence of reflection and represents the formation of a standing oscillatory system in which, as a result of a maximum possible constructive superposition at the reflector, the largest possible amplitudes related to the amplitudes at the entrance to the system of a wave occurs. This condition has not been reached in the Elbe estuary so far. However, there are signs that the resonance case is being approached.

The following contribution presents selected key parts of the research results from the RefTide project. A detailed version of the final report is available from the Leibniz Information Centre for Science and Technology University Library.