Abstract
Abstract. How storm events contribute to long-term shoreline change over decades to centuries remains an open question in coastal research. Sand and gravel coasts exhibit remarkable resilience to event-driven disturbances, and, in settings where sea level is rising, shorelines retain almost no detailed information about their own past positions. Here, we use a high-frequency, multi-decadal observational record of shoreline position to demonstrate quantitative indications of morphodynamic turbulence – “signal shredding” – in a sandy beach system. We find that, much as in other dynamic sedimentary systems, processes of sediment transport that affect shoreline position at relatively short timescales may obscure or erase evidence of external forcing. This suggests that the physical effects of annual (or intra-annual) forcing events, including major storms, may convey less about the dynamics of long-term shoreline change – and vice versa – than coastal researchers might wish.
Highlights
Quantifying magnitudes and rates of shoreline change is fundamental to understanding the dynamics of coastlines: how they behave over time, and how they may respond to future changes in environmental forcing
Following Jerolmack and Paola (2010), we find the hallmarks of morphodynamic turbulence in time series of shoreline position measured at Narrabeen–Collaroy Beach, in southeast Australia (Short and Trembanis, 2004; Harley et al, 2011a, 2015; Turner et al, 2016; Phillips et al, 2017)
The potential for beaches to “shred” large-magnitude changes in shoreline position forced at relatively short (∼ intra-annual) timescales complicates the reconciliation of short-term beach dynamics and longterm, spatio-temporal patterns of shoreline variability and evolution
Summary
Quantifying magnitudes and rates of shoreline change is fundamental to understanding the dynamics of coastlines: how they behave over time, and how they may respond to future changes in environmental forcing. Stormdriven shoreline excursions on the order of ∼ 101–102 m may be obscured within days to months, and effectively erased within years (Birkemeir, 1979; Egense, 1989; Thom and Hall, 1991; Morton et al, 1994; Douglas and Crowell, 2000; Honeycutt et al, 2001; Zhang et al, 2002; List et al, 2006; Lazarus et al, 2012; Lentz et al, 2013; Coco et al, 2014; Masselink and van Heteren, 2014; Phillips et al, 2017) This coastal context exemplifies a unifying challenge in geomorphology: determining how dynamic sedimentary systems – especially source-to-sink pathways – respond to rapid external forcing. The potential for beaches to “shred” large-magnitude changes in shoreline position forced at relatively short (∼ intra-annual) timescales complicates the reconciliation of short-term beach dynamics and longterm, spatio-temporal patterns of shoreline variability and evolution
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