Bed form genesis from bed defects under unidirectional, oscillatory, and combined flows

M. M. Perillo, E. W. Prokocki, J. L. Best, M. H. García

Research output: Contribution to journalArticle

Abstract

New experimental data on bed form initiation under unidirectional, oscillatory, and combined flows are presented to gain quantitative insight into bed form genesis from artificially generated defects on a flat sediment-laden bed. Planform changes revealed in time-lapse photography allowed study of the evolution of the downstream and upstream edges of defects from their initial geometric center. Based on this temporal data set and flow velocity profiles, it was observed that combined flow bed forms share the same bed form initiation processes as unidirectional and oscillatory flows, which are reflected directly in the generation of similar geometric patterns regardless of the hydrodynamic conditions. The development of these bed defects is strongly coupled to the direction and magnitude of the shear stress applied to the bed throughout the wave cycle. Under current-dominated combined flow conditions, no defect propagation occurred in the upstream direction, despite the presence of flow reversal. In addition, spectral analysis of the evolution of the downstream and upstream edges of the defects demonstrated that (i) periodicity in the defect growth pattern scales with the wave period for pure oscillatory flows; (ii) wave-dominated combined flows possess a period-driven peak with respect to defect growth in experiments with relatively short wave periods, but this peak is absent in experiments possessing relatively long wave periods (T >15s); and (iii) current-dominated combined flows and pure unidirectional flows do not display a period-driven peak in defect growth. These results suggest that the occurrence of long-period combined flow bed forms may be underrepresented in the sedimentary record.

Original languageEnglish (US)
Pages (from-to)2635-2652
Number of pages18
JournalJournal of Geophysical Research: Earth Surface
Volume119
Issue number12
DOIs
StatePublished - Dec 2014

Keywords

  • bed forms
  • bed forms initiation
  • combined flows
  • sediment transport
  • wave-current interaction

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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