Evaluation of the morpho-sedimentary diversity and multi-annual to multi-decadal dynamics of gravel barrier systems around the UK

Gravel barriers play an important role in protecting coastal communities and infrastructure along mid- to high-latitude shorelines. However, their ability to adapt and fulfil their protective role in the context of a global sea level rise and intensifying storm events remain uncertain. One the major obstacles to the creation of modelling tools for predicting the evolution of these coastal features is the diversity of their morpho-sedimentary character. Although gravel beaches are all characterized by a predominance of coarse-grained particles (> 2 mm), they are often mixed with varying amounts of finer sand particles, resulting in different beach sub-categories (e.g. pure gravel, composite, mixed sand-and-gravel). In addition to sediment variability (which links to sediment availability and supply), gravel beaches, like their sandy counterparts, organise themselves into various barrier landforms, such as spits, barrier beaches or beach ridge plains. It is commonly accepted that the morphodynamics of coastal barriers over several decades or centuries is closely tied to their geomorphological heritage that controls both accommodation space and sediment supply. The analysis of the environments surrounding the barrier is therefore just as important as the characterization of the barrier itself. Systemic approaches are usually considered at a local scale and rarely applied beyond the immediate sedimentary cell. To enhance consistency and gain a more comprehensive understanding of coastal barrier contexts and controls across the broader range of geomorphic contexts, a new approach of analysing these coastal features is needed.

An inventory of over 250 sites has identified gravelly shorelines around the UK, which have been subdivided according to beach and barrier types. Here, we demonstrate a framework for systematic morphometric analysis of gravel beach-barrier systems at the national scale. Barrier metrics (e.g. width, height, volume), inland topography, nearshore bathymetry and habitat mapping are extracted at a system scale that is divided into multiple segments to facilitate categorisation. The results represent a step forward towards a typology classification of gravel barrier systems. They also allow to highlight the importance of the various data sets when considering this approach, as well as identifying important gaps in data availability.