Taylor Perron: Environmental Fluid Mechanics/Hydrology – Defect Dynamics of Wave-generated Sand Ripples

Sand ripples generated by oscillatory flow beneath water waves, a familiar feature of beaches, have been studied for many years because they control bed roughness, record paleoenvironmental conditions, influence reservoir properties, and form visually arresting patterns. Yet remarkably little is known about how the crests and troughs that define these patterns adjust as waves and tides shift. We have conducted laboratory wave tank experiments and numerical simulations to discover the meaning of defects in wave ripples irregularities that disrupt an otherwise uniform array of crests and troughs that have been observed in modern environments and in ancient rocks. Time-lapse images of the laboratory experiments show how defects accommodate changes in the ripple wavelength as water waves vary. The numerical simulations explore the long-term evolution of the defects and their relationship to flow structures. We find that some defects are unique signatures of changes in wave height or water depth, and provide a window into ancient coastal environments, whereas others are similar to defects observed in many patterns composed of approximately parallel features, such as animal stripes and optical wave fronts.

Taylor Perron, Cecil & Ida Green CD Assistant Professor, Department of Earth, Atmospheric & Planetary Sceinces, MIT