Development of a shoreline change modelling system for Brandon Bay, Ireland using tide, wave and morphology models

Numerical models can play an important role in better understanding the coastal erosion process and the relative impacts of its drivers such as winds, waves and tides. The primary aim of this research was to develop a modelling system for simulation of shoreline change in Brandon Bay, located in Co. Kerry on the western coast of Ireland, and use the model to gain a deeper understanding of current circulation and wave climate in the bay and their impact on shoreline change. A secondary aim was to use the modelling system to study the potential impacts of future climate change on shoreline erosion/acretion. Hydrodynamic, spectral wave, and shoreline change models were developed using the well-known software packages Delft3D, SWAN and XBeach, respectively, and were validated against field measurements. The models revealed a strong wind influence in Brandon Bay, especially in its eastern half. This persists all year but is strongest during winter and is present even in the bottom layers. The model results showed that mean current speeds when wind was included in the model were 3-5 times higher than those when wind was omitted. The wave climate was characterised using a 7-year modelled wave dataset. Results showed significant seasonal variability in significant wave heights; winter means in the east of the bay ranged from 2-3 m compared to 0.5-1.0 m for summer. Five different storm wave classification approaches were used to identify storm wave characteristics from the modelled wave data. A fixed threshold approach, was found to be more effective for short-term periods (1-3 years), while a statistical-based classification using exceedance values was more suitable for longer periods (3+ years). The choice of approach had a significant effect on the number of identified storm waves which ranged from 36 to 136 for the most appropriate approaches. Coastline change was examined using cross-sectional profile datasets from surveys carried out between October 2021 and November 2022, paired with numerical model simulations. Erosion occurs mostly in the winter months, followed by natural recovery in the milder spring and summer seasons. The future climate model simulation showed that more intense storms in the future with increased wave height could cause increased coastal erosion and could the occurrence of more frequent storm waves.

Publisher

University Of Galway

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CC BY-NC-ND

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University of Galway Theses (PhD Theses)