Instability and finite-amplitude self-organization of large-scale coastline shapes
Murray, A. Brad
Ashton, Andrew D.
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KeywordCoastlines; Pattern formation; High-angle waves; Emergent structures; Non-‐local interactions
Recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross-shore extent of active sediment transport. A simple morphodynamic instability arises from the feedback between wave-driven alongshore sediment flux and coastline shape. Coastline segments with different orientations experience different alongshore sediment fluxes, so that curvatures in coastline shape drive gradients in sediment flux, which can augment the shoreline curvatures. In a simple numerical model, this instability, and subsequent finite-amplitude interactions between pattern elements, lead to a wide range of different rhythmic shapes and behaviours—ranging from symmetric cuspate capes and bays to alongshore migrating ‘flying spits’—depending on the characteristics of the input wave forcing. The scale of the pattern coarsens in some cases because of the merger of migrating coastline features, and in other cases because of non-local screening interactions between coastline protrusions, which affect the waves reaching other parts of the coastline. Features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies. Initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature.
Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of The Royal Society for personal use, not for redistribution. The definitive version was published in Philosophical Transactions of the Royal Society of London Series A-Mathematical Physical and Engineering Sciences 371 (2013):20120363, doi:10.1098/rsta.2012.0363.
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Reply to comment by M. Ortega-Sánchez et al. on “High-angle wave instability and emergent shoreline shapes : 1. Modeling of sand waves, flying spits, and capes” Ashton, Andrew D.; Murray, A. Brad (American Geophysical Union, 2008-01-26)
High-angle wave instability and emergent shoreline shapes : 2. Wave climate analysis and comparisons to nature Ashton, Andrew D.; Murray, A. Brad (American Geophysical Union, 2006-12-15)Recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore, giving rise to an instability ...
High-angle wave instability and emergent shoreline shapes : 1. Modeling of sand waves, flying spits, and capes Ashton, Andrew D.; Murray, A. Brad (American Geophysical Union, 2006-12-15)Contrary to traditional findings, the deepwater angle of wave approach strongly affects plan view coastal evolution, giving rise to an antidiffusional “high wave angle” instability for sufficiently oblique deepwater waves ...