Abstract
AbstractHigh energy, rocky coastlines often feature sandy beaches within headland‐bound embayments. Not all such embayments have beaches however, and beaches in embayments can be removed by storms and may subsequently reform. What dictates the presence or absence of an embayed beach and its resilience to storms? In this paper, we explore the effect of offshore slope and wind conditions on nearshore sediment transport within idealised embayments to give insight into nearshore sediment supplies. We use numerical simulations to show that sand can accumulate near shore if the offshore slope is >0.025 m/m, but only under persistent calm conditions. Our modelling also suggests that if sediment in an embayment with an offshore gradient steeper than 0.025 m/m is removed during a period of persistent stormy conditions, it will be unlikely to return in sub‐decadal timescales. In contrast, sediment located in embayments with shallower gradients can reform swiftly in both calm and stormy conditions. Our findings have wide implications for contemporary coastal engineering in the face of future global climate change, but also for Quaternary environmental reconstruction. Our simple method to predict beach stability based on slope can be used to interpret differing responses of embayments to periods of changing coastal storminess such as the medieval climate anomaly‐little ice age (MCA‐LIA) transition. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Highlights
Numerous factors control the form and persistence of sandy beaches, including sediment supply, incident wave direction, alongshore and cross-shore sediment transport mechanisms, and tidal range (Masselink and Short, 1993; Masselink and Pattiaratchi, 2001; van Rijn et al, 2003; Aagaard et al, 2004; Cooper et al, 2004; Austin et al, 2009)
Landscape-scale models of beach and headland erosion have focused on sediment supply from headland erosion to maintain beaches (Limber and Murray, 2011), but less attention has been paid to the sediment transport dynamics that may promote or inhibit beach formation and stability
If we further explore the change in sediment flux observed in Figure 9(b) when climatic conditions briefly switch from stormy to calm, Figure 11 shows the impact on shoreward volume of switching climatic conditions halfway (i.e. 5 years) into the simulation: Change in volume flux as slope increases is sensitive in a nonlinear fashion to a stepwise change from calm to stormy conditions (Figure 11(a))
Summary
Numerous factors control the form and persistence of sandy beaches, including sediment supply, incident wave direction, alongshore and cross-shore sediment transport mechanisms, and tidal range (Masselink and Short, 1993; Masselink and Pattiaratchi, 2001; van Rijn et al, 2003; Aagaard et al, 2004; Cooper et al, 2004; Austin et al, 2009). Is the desirability of living by the coast a major economic factor, with associated tourism and recreational activities, and beaches and coastlines hold many cultural and archaeological sites. Understanding what drives their formation, stability and distribution is crucial for effective management strategies and adaptation in the face of future climate change (Zhang et al, 2004; Dawson, 2013). Beach sediment is eroded during storm events and often lost offshore, but beaches can recover these sediments gradually over seasonal to decadal timescales (Harley et al, 2015; Scott et al, 2016)
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