Modelling Gravel-Dominated Inlet Morphodynamics

This thesis investigates the morphodynamics of a gravel-dominated inlet system at the Deben Estuary, southeast UK, with a focus on cyclic behaviour, sediment bypassing pathways, and the combined influence of waves, tides, and large-scale climate drivers. Using long-term bathymetric records (1991–2023), multivariate statistical analyses, sediment mapping, numerical modelling, and field validation, the research provides new insights into the processes that shape gravel-dominated inlet systems. Results show that the Deben ebb-tidal delta follows variable cyclic behaviour, with delta volume growth driven by periods of sediment influx and subsequent redistribution. Changes in the wave climate, particularly the balance between NE and S wave forcing, play a central role in controlling bypassing processes and morphological adjustments. Sediment analysis demonstrates that gravel is the dominant fraction, and both waves and tidal currents are competent to transport coarse material under energetic conditions. Different wave directions drive distinct alongshore and cross-shore pathways, which together promote morphological complexity, swatchway evolution, and shoal migration. Hydrodynamic modelling highlights that tides play a stronger role in gravel-dominated inlet systems than traditionally assumed, with spring tidal flows capable of moving gravel. Tide-wave interactions further influence flow patterns, sediment transport, and bypassing pathways, with contrasting behaviours between spring and neap conditions. On a broader scale, inlet dynamics are shown to be sensitive to climate variability, with the North Atlantic Oscillation strongly linked to wave forcing patterns and long-term delta volume changes.