Abstract
Time scales of post-storm nearshore morphological recovery and physical processes governing these time scales are poorly understood at present. The ability to predict nearshore morphological recovery time scales based on pre-, during- or post-resetting storm conditions is an essential requirement for building and validating scale aggregated models that operate at macro- and higher spatio-temporal scales. In this study, quality controlled ARGUS video derived beach states at Palm Beach, Sydney (4 years) and Duck, NC (2 years) and concurrent wave data are analysed to quantify the nearshore morphological recovery time scales (Tmr) and to determine the physical processes that may govern Tmr. The results show that Tmr is of the order of 5-10 days at these two beaches. Tmr is moderately positively correlated with the averaged longshore current over the 3 days immediately after the resetting storm, indicating that it might be possible to develop a predictor for Tmr based on wave conditions immediately after the resetting storm. Weak correlations are present between Tmr and several pre-storm, during-storm and post-storm parameters at the two sites. However, these correlations are inconsistent between the two sites. A thorough analysis employing long-term beach state and wave data at several different study sites is required to fully understand this phenomenon.
Highlights
How long does it take for nearshore morphology to recover after a storm induced morphological reset event? Is the morphological recovery time scale (Tmr) more or less the same at beaches with similar characteristics, or is it completely random? Are there any physical processes that govern Tmr, or is it governed by scale-aggregated self-organising behavioural characteristics? These are important questions that need to be answered to further our understanding of macro-scale coastal behaviour, which is a prerequisite to build and validate predictive models at macro- and higher spatio-temporal scales
It is noteworthy that previous numerical modelling efforts which mimicked Palm beach conditions predicted recovery durations that are 50% lower (Reniers et al, 2004) or 50% higher (Damgaard et al, 2002) than the observed Tmr of 11 days at Palm beach
While Tmr at the single barred Palm beach (11 days) is double that of the double barred Duck beach (5 days), whether morphological recovery is generally slower at single barred beaches relative to double barred beaches is a question that cannot be conclusively answered without investigating this phenomenon at several other sites
Summary
How long does it take for nearshore morphology to recover after a storm induced morphological reset event? Is the morphological recovery time scale (Tmr) more or less the same at beaches with similar characteristics, or is it completely random? Are there any physical processes that govern Tmr, or is it governed by scale-aggregated self-organising behavioural characteristics? These are important questions that need to be answered to further our understanding of macro-scale coastal behaviour, which is a prerequisite to build and validate predictive models at macro- and higher spatio-temporal scales. How long does it take for nearshore morphology to recover after a storm induced morphological reset event? Is the morphological recovery time scale (Tmr) more or less the same at beaches with similar characteristics, or is it completely random? Coastal management/planning decision support tools that account for long term (decadal to centennial) coastline behaviour (e.g. Callaghan et al, 2008; Ranasinghe et al, 2012) will greatly benefit from a knowledge of Tmr because it is unlikely that dune recovery will occur before the nearshore morphology recovers after storm induced resets (i.e. initiation of dune recovery will almost always occur after Tmr has been reached). To date, there has been no concerted research effort focussing on the important issue of nearshore morphological recovery time scales. The present study takes an initial step towards addressing this knowledge gap
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