This thesis considers the influence of gravel barrier dynamics on coastal erosion and flooding risk. Establishing the potential for coastal landforms to provide effective risk reduction is salient given growing momentum behind coastal management approaches seeking to incorporate ‘natural’ processes and landforms into more conventional strategies.

Chapter 1 begins by establishing the value of risk-based approaches to coastal management. Coastal erosion and flooding are identified as two commonly experienced risks which often interact on gravel barrier coastlines. Through reviewing the coastal erosion, flooding, and gravel barrier morphodynamics literature, this chapter identifies a series of research opportunities which inform three research questions:

1. How can we variously define shoreline position and morphology to explain the diversity of gravel barrier morphodynamics over centennial to event timescales?
2. To what extent can management regime change alter erosion-flooding interactions in gravel barrier settings, particularly during storm surge events?
3. How may gravel barriers evolve over the next 100 years and what are the coastal risk management implications of this evolution?

Chapter 2 introduces the Blakeney Point Barrier System (BPBS), a mixed sand-gravel barrier located on the UK’s North Norfolk coast, as an illustrative case study. The BPBS is characterised by vulnerability to low frequency, high magnitude storm surge events; a history of active intervention (re-profiling of the barrier crest into a heightened and steepened form) which has recently ceased; and the provision of flood protection to landward communities and ecosystems. The opportunity to investigate these characteristics and their implications for geomorphological evolution, erosion and flooding risk derive from 130 years of quasi-continuous remote-sensing and field observations.

Chapters 3 and 4 describe the thesis methodology which comprises shoreline change analysis and numerical modelling. Chapter 3 outlines the datasets available for shoreline change analysis which include historical maps, vertical aerial photographs, LiDAR (light detection and ranging) elevation surveys, cross-shore topography profiles, hydrodynamic and weather times series. Then five unique shoreline proxies are defined, and the shoreline extraction and validation procedures associated with each are described. Chapter 4 describes a numerical model chain which simulates storm surge water levels at the basin scale (TELEMAC), waves in the nearshore zone (SWAN), and hydrodynamic and morphological change at a series of cross-shore profiles along the BPBS (XBeach-Gravel). Robust calibration and validation using data collected from the 5 December 2013 storm surge is undertaken, followed by application to future sea level rise scenarios.

Results and subsequent discussion are divided among Chapters 5, 6, and 7. Chapter 5 emphasises the importance of rigorous error analysis to ensure that measured shoreline changes can be distinguished from the noise introduced by shoreline definition and extraction procedures. It then establishes the value of extracting multiple shoreline proxies to encourage a fuller understanding of coastal evolution over multiple temporal scales. Chapter 6 argues that while coastal erosion and flooding represent hazards in their own right, they also interact and this interaction must be incorporated into coastal risk management strategies. It also provides a detailed analysis of the impact of recent management regime changes along the BPBS on coastal erosion and flooding outcomes. Chapter 7 considers barrier resilience with a focus on forecasting future shoreline positions and the ways in which the BPBS may respond to storm surges under a range of future sea level rise scenarios.

In concluding, this thesis establishes a central role for gravel barrier dynamics when assessing coastal erosion and flooding risk, particularly as natural landforms are integrated into existing coastal risk management strategies and expected to provide flood risk reduction under future storm surge forcing and sea level rise.