Modelling sand transport and coastal morphology

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Modelling sand transport and coastal morphology

• Jebbe van der Werf1, Jan Ribberink1 and Tom
  ODonoghue2
• 1University of Twente and 2Aberdeen University,
  Scotland
• SANTOSS project funded by UKs EPSRC
  (GR/T28089/01) and Dutch research organisation
  STW (TCB.6586)

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Introduction

• Important to understand and to be able to predict
  future changes coastal and seabed morphology
• Morphological models require accurate practical
  sand transport model
• Existing models give inaccurate prediction
  wave-induced sand transport

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Existing transport models

• Quasi-steadiness
• Asymmetric wave ? (onshore)
• e.g. Bailard (1981), Ribberink (1998), Van Rijn
  (1993, 2000, 2004)

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Wave-induced sand transport
100 laboratory exps non-breaking waves D50
0.13 0.87 mm T 5.0 12.5 s
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Wave-induced sand transport
quasi-steady models work fine for number of cases
but fail in case of...
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Wave-induced sand transport

• quasi-steady models work fine for number of cases
  but fail in case of...
• phase lag effects

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Wave-induced sand transport

• quasi-steady models work fine for number of cases
  but fail in case of...
• phase lag effects
• acceleration effects

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Wave-induced sand transport

• quasi-steady models work fine for number of cases
  but fail in case of...
• phase lag effects
• acceleration effects
• surface wave effects

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SANTOSS project (2005-2008)

• Establish new practical model for sand transport
  induced by non-breaking waves and currents
• incorporate phase lag effects based on existing
  knowledge and data (reported here)
• incorporate acceleration and surface wave effects
• full-scale surface wave experiments (delta flume,
  GWK)
• full-scale sawtooth oscillatory flows exps
  (AOFT, LOWT)
• process-based model research

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New transport model

• Semi-unsteady
• Potential transport in crest and trough direction
• Distribution potential transports over half
  cycles depending on phase lag parameters

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Phase lag effects

• Concentration lacks behind velocity since
  particle entrainment and settling takes time
• Phase lag parameter

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New transport model

• Computation net transport vector

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Data used for model calibration
136 oft experiments mainly wave-dominated collinea
r currents D50 0.13 0.46 mm T 4 12 s R
uc / (uc ut) ? 0.7
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Calibration results
?s 3.7 ?r 0.83 m 3.9 (n 1.5) (Pcr
1.0) 66 within factor 2 91 within factor 5 94
within factor 10
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Application new transport model

• Implementation in morphological models
  (Unibest-TC, Delft-3D)
• Application to practical scenarios with good
  measurements of morphological change
• study effects transport processes
• compare with currently-implemented transport
  models

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LIP experiments

• bar migration due to on- and offshore transport
  components
• when is which component important?

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GWK experiments
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Conclusions

• Existing models give inaccurate prediction
  wave-induced sand transport
• New general practical sand transport model based
  on large data set from oft experiments
• Main improvement description wave-related
  transport, particularly phase lag effects
• Future work
• incorporate acceleration and surface wave effects
• application to morphological scenarios