Direct measurements of bed shear stress under swash flows on steep laboratory slopes at medium to prototype scales

Daniel Howe, Chris E. Blenkinsopp, Ian L. Turner, Tom E. Baldock, Jack A. Puleo

Research output: Contribution to journalArticlepeer-review

6 Citations (SciVal)


Robust measurements of bed shear stress under wave runup flows are necessary to inform beachface sediment transport modelling. In this study, direct measurements of swash zone bed shear stress were obtained in medium and prototype-scale laboratory experiments on steep slopes. Peak shear stresses coincided with the arrival of uprush swash fronts and high-resolution measurement of swash surface profiles indicated a consistently seaward sloping swash surface with minimal evidence of a landward sloping swash front. The quadratic stress law was applied to back-calculate time-varying friction factors, which were observed to decrease with increasing Reynolds number on smooth slopes, consistent with theory for steady flows. Additionally, friction factors remained relatively constant throughout the swash cycle (except around flow reversal), with a variation of approximately ±20% from the mean value and with only small differences between uprush and backwash. Measured friction factors were observed to be larger than expected when plotted on the Moody or wave friction diagram for a given Reynolds number and relative roughness, consistent with previous field and laboratory studies at various scales.

Original languageEnglish
Article number358
JournalJournal of Marine Science and Engineering
Issue number10
Publication statusPublished - 9 Oct 2019


  • Bed shear stress
  • Friction coefficient
  • Runup
  • Shear plate
  • Swash

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Water Science and Technology
  • Ocean Engineering


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