Environmental signal shredding on sandy coastlines

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.

Will Nature Work With Us? Erosion and Flooding Impacts on a Uk Barrier

“…Overwash has been identified as a key process for explaining barrier response to changing environmental conditions (Masselink and Van Heteren 2014) and represents an example of instantaneous erosion-flooding interaction (Pollard et al 2018). The role of overwash in shoreline retreat is challenging to establish in the absence of high resolution shoreline reconstruction owing to morphological 'signal shredding' (Lazarus et al 2019) whereby shorelines undergoing persistent retreat under sea level rise retain limited information about their past position. Here, through extracting the vegetation line at near annual frequency, it is possible to quantify shoreline retreat resulting from overwash.…”

Understanding spatio-temporal barrier dynamics through the use of multiple shoreline proxies

“…Owing to its location towards the landward limit of the beach profile, the Vegetation Line is effective at recording and preserving extreme event impacts. Locations closer to mean sea level on the beach profile are more exposed to post-event recovery processes (Brooks et al, 2017;Lazarus et al, 2019) making the morphological impact of storm surge events difficult to isolate when vertical aerial photographs are only captured annually. Landward rollover of the Cley-Salthouse barrier during storm surges has long been identified as one of the key forms of sediment movement at Blakeney Point (Clymo, 1967); following the storm surge of 31 January -1 February 1953, Steers and Grove (1953) estimated an average barrier rollover of 27-37 m. However, when calculated as a mean annual rollover rate, the retreat of the Cley-Salthouse barrier based on the Vegetation Line has been less, at 0.91 m a -1 , than rates recorded for barriers elsewhere (e.g.…”

Defining Coastal Resilience

“…By this definition, resistance is a capacity exerted before the system is perturbed; resilience can be measured after the perturbation has occurred. In geomorphic systems-especially sediment-transport systems-the impacts of physical disturbances can be filtered and disproportionately attenuated (through negative feedbacks), rather than amplified (through positive feedbacks) [92][93][94]. In some cases, such as in well-developed beach cusps [95] or large-scale cuspate forelands [96] that inhibit the development of smaller-amplitude wavelengths, a negative feedback underpins resilience by reinforcing equilibrium and/or pattern stability [97]-and the presence of the negative feedback itself constitutes a kind of resistance.…”

“…Although resilience is closely linked to dynamical stability, resilient coasts are not necessarily stable coasts. Given that resilience in geomorphic systems is sensitive to local geography and historical legacies [94], blanket conclusions about the relative resilience of particular types of landforms or landscapes (e.g., barrier islands, tidal wetlands, coral atolls) become problematic. And nowhere is the fallacy of stable coasts more important than on developed shorelines.…”