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Abstract(s)
Coastal areas face increasing pressure from urbanization and human activities, exacerbating erosion and environmental challenges. Coastal engineering structures, such as breakwaters, groins, seawalls, and jetties, have been used to stabilize beaches, but often prove inadequate. Beach nourishment has emerged as a promising alternative; however, significant challenges remain in assessing sediment transport associated with shoreface nourishments, and in understanding their efficiency and longevity. This thesis aims to enhance the understanding of sediment dynamics in the upper shoreface of wave-dominated coastal environments, with a focus on optimizing sediment management and improving the long-term sustainability of shoreface nourishments. To achieve these objectives, this research employs a multi-faceted approach combining physical experiments, field data collection, and numerical modelling.
Chapter 3 describes a physical model experiment using magnetic tracers to measure sediment transport in a controlled environment. The effectiveness of the magnetic tracers is compared to fluorescent tracers in an experiment conducted in the large wave flume (Großer Wellenkanal, GWK)in Hannover. Results showed similar dispersion patterns and net transport rates for both tracers, though the magnetic tracers exhibited lower recovery rates, indicating the need for further research. Wave streaming emerged as a key process driving sediment transport under non-breaking waves in the direction of wave propagation.
In chapter 4, field measurements, including a tracer experiment, are combined with numerical modelling to assess sediment transport in the shoreface of Costa Nova, Aveiro. The Delft3D model is used to simulate the interaction of waves, currents, sediment transport, and morphology in this complex, energetic environment. Data from the tracer experiment validate the model’s performance. A Lagrangian model is also developed to estimate sediment particle pathways based on the simulated transport fields. The results reveal that onshore bed load transport dominates during calm conditions, while longshore suspended transport prevails during moderate wave energy events. These findings improve the understanding of shoreface sediment dynamics.
In chapter 5, the implemented numerical model is applied to analyse the processes and dynamics of a shoreface nourishment conducted in Costa Nova in the summer of 2020. A short- and seasonal-term analysis of the nourishment’s evolution highlights the critical role of incident wave conditions, particularly during moderate to energetic events. These conditions not only protect the beach by dissipating wave energy but also nourish adjacent areas through sediment spreading. A conceptual model is presented that illustrates the short- and seasonal-term impacts of the nourishment. In the short term, the nourishment behaves as a detached breakwater, affecting hydrodynamics; at a seasonal term, sediment redistribution contributes to both the subaerial and submerged beach.
The thesis develops tools to support the optimization of nourishment placement to enhance its effectiveness. Future research should focus on refining model accuracy through better sediment characterization and improved acceleration techniques. This work contributes to the understanding of shoreface nourishment and supports sustainable coastal protection strategies.
Description
Keywords
numerical modelling morphodynamics sediment transport sediment tracers shoreface nourishment modelação numérica morfodinâmica transporte sedimentar traçadores sedimentares alimentação na praia submarina