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Geo-Marine Letters

, Volume 31, Issue 4, pp 249–258 | Cite as

Coupled penetrometer, MBES and ADCP assessments of tidal variations in surface sediment layer characteristics along active subaqueous dunes, Danish Wadden Sea

  • Nina StarkEmail author
  • Hendrik Hanff
  • Christian Svenson
  • Verner B. Ernstsen
  • Alice Lefebvre
  • Christian Winter
  • Achim Kopf
Original

Abstract

In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ∼1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1–3 kPa in the top layer, 20–140 kPa in the underlying sediment; thickness of the top layer ca. 5–8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 ± 2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments.

Keywords

Tidal Cycle Acoustic Doppler Current Profiler Backscatter Intensity Sediment Mobilization Sediment Strength 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

We acknowledge the German Research Association (via MARUM, Center of Excellence at the University of Bremen, and GLOMAR, Bremen International Graduate School for Marine Sciences) for funding this study. We thank the crew of the R/V Senckenberg for support. We are particularly indebted to Matthias Lange (MARUM) and Matthias Colsmann (AVISARO, Hannover). Also, the manuscript benefited significantly from comments by an anonymous reviewer and the journal editors.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Nina Stark
    • 1
    Email author
  • Hendrik Hanff
    • 1
  • Christian Svenson
    • 1
  • Verner B. Ernstsen
    • 1
  • Alice Lefebvre
    • 1
  • Christian Winter
    • 1
  • Achim Kopf
    • 1
  1. 1.MARUM-Center for Marine Environmental SciencesBremenGermany

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