Abstract
Sand and gravel beaches naturally act as a coastal buffer, absorbing wave energy and dynamically adapting to the seasonal and long-term wave climate. Significant shifts in nearshore morphology can occur during extreme wave events, which can have a significant impact on coastal vulnerability. During the winter of 2013/14, the Atlantic coast of Europe received an unprecedented sequence of very energetic wave conditions (8-week mean offshore Hs=4.4m). These events caused extensive physical (beach and dune erosion) and socio-economic (flooding, damage to infrastructure) impacts throughout the west coast of Europe. Many monitored sites in the UK and France were in their most eroded state since morphological records began (5–10years). We consider the geomorphological significance of the storm response at 38 natural beaches in the southwest of England, ranging from semi-sheltered reflective gravel barriers to ultra-dissipative exposed sand beaches with dunes. The extent and patterns of post-storm recovery are examined in detail at three beaches with characteristic storm response behaviours. Exposed sandy beaches were dominated by cross-shore transport processes leading to significant loss of sediment offshore from the intertidal zone (>200m3/m); exposed gravel beaches were dominated by overwash with significant loss landward; and semi-sheltered sites exposed to more oblique wave forcing were dominated by a rotational response due to alongshore sediment redistribution. Due to these contrasting responses, mechanisms and timescales for beach recovery displayed strong inter-site and intra-site variations. In offshore and rotational cases, the recovery processes were multi-annual, comprising seasonal to decadal signals and were intrinsically linked to the storm response mechanisms, while permanent losses occurred when overwash dominated. We show that post-storm recovery does not necessarily occur during calm periods and that in many cases high-energy wave events appear to be essential for recovery of sediment (offshore and counter-rotation). Our results highlight the significance of dominant climatic oscillations, multi-annual storm sequencing, storm tracks and resultant variations in wave angle, in controlling the impact that extreme wave events have on contrasting sand/gravel beaches in exposed/sheltered locations.
Highlights
Sand and gravel beaches naturally act as a coastal buffer (Stive et al, 2002), absorbing wave energy and dynamically adapting to the seasonal and long-term wave climate
Scott et al / Marine Geology 382 (2016) 224–241 has been lost to the system, either offshore, alongshore or landward. It is the balance between storm response, storm frequency and recovery rates that controls the long-term coastal evolution and vulnerability, but our understanding of coastal storm response is limited by the quality and appropriateness of the datasets available (Coco et al, 2014), for quantitative measurements throughout a full sequence of beach recovery
Total sediment volume loss and intertidal beach lowering throughout the exposed west coast beaches was dramatic, exceeding − 100 m3/m and representing a lowering of ~0.5 m in many cases
Summary
Sand and gravel beaches naturally act as a coastal buffer (Stive et al, 2002), absorbing wave energy and dynamically adapting to the seasonal and long-term wave climate. High-energy wave events will mobilise offshore sediments at depth, advected by storm driven nearshore currents, like bed return flow (e.g., Roelvink and Stive, 1989; Özkan-Haller, 2013) and rip currents (e.g., Loureiro et al, 2012), modifying the position of offshore bars and shoals, and nearshore wave transformation (Senechal et al, 2011; Coco et al, 2014; Lewis et al, 2014). These erosional responses can result in reduced or modified beach levels, which have short- to medium-term impacts for coastal vulnerability (Masselink et al, 2015). It is the balance between storm response, storm frequency and recovery rates that controls the long-term coastal evolution and vulnerability, but our understanding of coastal storm response is limited by the quality and appropriateness of the datasets available (Coco et al, 2014), for quantitative measurements throughout a full sequence of beach recovery
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