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The influence of lagoons on large-scale tidal dynamics: an idealized modelling study

Hermann, K. M. (2020) The influence of lagoons on large-scale tidal dynamics: an idealized modelling study.

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Abstract:Complex numerical modelling studies of the Adriatic Sea suggest that tidal inlet systems such as the Venice lagoon have a significant impact on the tidal dynamics, affecting the entire Adriatic Sea. However, the underlying physical mechanisms are not yet understood. We present an idealized modelling study to investigate the tidal interaction between lagoons and an adjacent sea. To model the tidal interaction between a lagoon and a sea, a classical Taylor model is combined with a Helmholtz basin at the closed end. We studied the in uence of so-called sub-critical lagoons (with an eigenfrequency above the forcing tidal frequency) and super-critical lagoons (with an eigenfrequency below the forcing tidal frequency) on the tidal dynamics of the sea with a parameter sensitivity analysis. The physical mechanism induced by a lagoon, affecting the large-scale tidal dynamics of the sea, involves a radiating wave originating from the lagoon. This radiating wave causes a phase-shift of the re ected Kelvin wave, resulting in an along-basin shift of the amphidromic system. Additionally, enhanced energy dissipation due to bottom friction in the inlet channels of the lagoon leads to a cross-basin shift of the amphidromic point. Finally, we tested our model by comparing a simulation of the Adriatic Sea with the results of the abovementioned complex model. Effects of the tidal interaction between the lagoons and the Adriatic Sea of the idealized model showed good agreement with the results of the aforementioned complex model. The results confirmed that lagoons affect the tidal dynamics of the entire Adriatic Sea. Additionally, we showed that the simulated shift in the amphidromic point in the Adriatic Sea occurs due to the sub-critical nature of the lagoons. Our results indicate that | as the proximity to resonance of the lagoon governs the response in the adjacent sea | altering the geometry of the lagoons (e.g. through dredging operations) may cause back-effects in the adjacent sea.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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