Presently our understanding of gravel beach response under wave attack is limited and approaches to predict gravel beach response rely on formulae and models based on a few physical modelling studies. Field and laboratory studies (Hawkes, Coates, and Jones (1998)) indicate the importance of complex wave spectra (combining swell and wind sea) in the design of gravel beach recharge schemes.
The objective of the study was to develop a data-set and a new parametric model, Shingle-B, to analyse the generic profile response of shingle beaches under bimodal wave conditions in order to increase confidence in beach cross section design. A mobile bed flume study was therefore carried out at HR Wallingford.
This paper describes both the design and the results of the 2D physical model study.
Beaches consisting of gravel (2 to 64 mm), pebbles and cobbles (64 to 256 mm) are generally known as coarse beaches or shingle beaches along the English coastline and can be found in many mid / high-latitude regions (formerly glaciated) of the world (UK, Iceland, Canada, etc.). Gravel and barriers beaches around England and Wales are regarded as a highly effective coastal defence due to the efficiency of dissipating wave energy, and protection against coastal flooding.
Gravel beaches have received less attention than sandy beaches, resulting in a lack of data on storm response. Consequently current empirical models (Powell 1990; Bradbury 2000) remain the only sources for coastal managers to predict profile response.
A sea-state is composed of either wind-sea, swell-sea or a combination of the two (bimodal sea-state). Wind-seas are generated by local winds; their impacts at the coast in terms of overtopping, beach movement, etc., are relatively well understood for many simple configurations.
Swell waves, produced as wind waves decay after a storm, have longer periods than locally generated storm waves (wind-sea), although usually lower wave heights.
The spectral shape of a sea-state will show where the principal proportion of the wave energy is and what the wave heights and wave periods are. The spectral parameters derived from wave spectra, principally wave height and period, are one of the most widely used descriptions for waves used in design and prediction methods in coastal/maritime environments. The distribution of the spectral energy may be more important than the wave period or the wave height, though conventional methods of analysis will generally only use these basic parameters.