Patterns in the sand Seminar

Abstract

The nearshore region exhibits many striking morphological patterns with a variety of spatial and temporal scales (ripples, beach cusps, sandbars). The formation of these rhythmic features has been initially ascribed, depending on the pattern in question, to spatial structures in the flow or geological constrains. These forcing templates have been hypothesized to provide the spatial structure that becomes imprinted on the shoreline or seabed morphology. More recently, new explanations for rhythmic patterns have involved interactions between fluid flow and sediment transport that create morphological feedbacks and lead to pattern self-organization. I will illustrate the sweeping shift from template explanations to self organization by discussing different nearshore patterns. Models involving self organization show that local interactions between flow and sediment transport can collectively give rise to patterns with large-scale coherence and that the driving feedbacks can be associated with either topographical or grain-size composition instabilities. An approach based on self-organization also allows researchers to establish limitations in the predictability of rhythmic pattern occurrence and characteristics as well as to study mechanisms leading to the observed pattern variability or lack of regularity.