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 un-
derstanding 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 espe-
cially of the effects of multiple reflections and re-reflections. Within the BMBF-funded
KFKI-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 estu-
aries. The Elbe estuary was chosen as the 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 mod-
els with empirical studies based on available time series of water level and flow data. In
addition, in RefTide methods for resonance analysis were (further) developed and applied
to the Elbe estuary.
The reflection behaviour of tidal waves was investigated model-based using a self-de-
veloped analytical model as well as on a large number of model tests with different hydro-
dynamic 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 dissi-
pation 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 re-
flection 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 am-
plitudes 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 (Hamburg Port Authority and
Technische Universität Hamburg 2022) is available from the Leibniz Information Centre
for Science and Technology University Library.