Morphometric classification of swell-dominated embayed beaches

Abstract

Globally, embayed beaches are common to hilly and mountainous coastlines. They are typically characterised by two headlands that are a primary control on incident wave exposure and beach morphodynamics. Embayed beaches exist under a range of headland morphologies and degree of embaymentisation. Here, we present a generalised embayment morphometric parameter (γe) which classifies the geomorphological setting of embayed beaches based on the embayment indentation and area. We apply this to 168 swell-dominated embayed beaches from 6 regions using open-access imagery. The embayment morphometric parameter (γe) was subjected to k-means cluster analysis to identify 4 classes of embayed beaches with increasing γe indicating greater headland influence and impact on incident wave exposure. The Classes range from 1 to 4 with increasing degree of embayment. The most common is Class 2 (43%, n = 73) which represents embayed beaches that have moderate embayment indentation and headland influence. There are clear trends in embayment geometry regardless of location, wave climate or tidal regimes. Within the embayments, there were 6 possible headland orientations (types H1–H6). The most common (58%, n = 97) is when both headlands are orientated outwards from the beach (H6) and may result in greater morphological beach response from less headland shadowing, compared with headlands orientated inwards onto the beach (H1). In summary, we have developed a simple classification scheme for embayed beaches based on degree of indentation and headland orientation that can be applied to any embayed beach globally.