Classification of beach morphodynamic state relies on accurate representation of breaking wave conditions, Hb (plus grain size and spring tidal range). Measured breaking wave data, however, are absent from all but a handful of sites worldwide. Here, we apply process-based wave modelling for propagating offshore waves to the breaking zone using high-resolution nearshore bathymetry, obtaining representative and accurate Hb values for multiple beaches at regional scale, and thereby derive meaningful morphodynamic classifications that accord with observed beach state. Ninety-five beaches on the north coast of Ireland were investigated, with observed beach types and states compared to predictions based on morphodynamic parameters determined using wave, tide and sediment data, obtained from field surveys and detailed numerical wave modelling. The coast is exposed to micro-through meso-tides (0.43–3.90 m) and low sea through high swell waves (Hb = 0.13–1.18 m) and is composed of fine to medium sand resulting in a full range of beach types (wave-dominated, tide-modified and tide-dominated) and most beach states, thereby providing a comprehensive field laboratory to undertake such a comparison. We found that modal beach types reside within their predicted Relative Tide Range (RTR) and modal beach states close to the predicted dimensionless fall velocity (Ω) range. The use of high-resolution nearshore wave modelling to determine Hb was deemed the most appropriate approach for deriving predicted beach classification. The work follows the investigation of the same coast by Jackson et al. (2005) who found shortcomings in relating beach types to breaker wave conditions. However, advances in inshore wave modelling and access to high-resolution nearshore bathymetry since then have enabled improved estimates of breaker height, producing more accurate results and enhancing previous work. The results highlight the need to obtain accurate estimates of Hb and Tp if they are to be used effectively in predicting beach parameters. This work therefore sets a precedence for other coastal sites worldwide where detailed nearshore bathymetry is available and Hb can be derived from process-based wave modelling, improving the classification and prediction of morphodynamic beach type and state.
Bibliographical noteFunding Information:
Access to high-resolution bathymetric data was provided by the Integrated Mapping for the Sustainable Development of Ireland's Marine Resource (INFOMAR) project, a joint seabed mapping project between the Geological Survey of Ireland (GSI) and the Marine Institute. The use of the Joint Irish Bathymetric Survey dataset was made possible by the Maritime and Coast Guard Agency (UK), the Marine Institute of Ireland, the Northern Ireland Environment Agency (NIEA) and the GSI and Geological Survey of Northern Ireland (GSNI). Bathymetric data from the UK Marine Environmental Data and Information Network (MEDIN) was made available through the UK Hydrographic Office Admiralty Marine Data Portal. We would also like to acknowledge the UK Met Office for the hindcast wave data. LANDSAT imagery was available from the US Geological Survey Earth Explorer Platform. The POLPRED2 software was kindly provided by the National Oceanographic Centre, UK. Finally, we wish to thank Dave Rogers (Ulster University) for his diligent assistance with field sampling, sediment and tide analysis. This is a contribution to Natural Environment Research Council project NE/F019483/1.
© 2022 The Authors
- Beach state
- Beach type
- Breaker wave height
- Tide range