New high resolution measurements of Sand transport processes under fullscale surface waves

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New high resolution measurements ofSand
transport processes under full-scale surface
waves

• Jolanthe Schretlen
• Jebbe van der Werf, Maarten Kleinhans, Joris
  Eekhout,
• Michel Zuijderwijk, Jan Ribberink, Tom ODonoghue
  a.o.

GWK Coastal Research Centre, Hannover HYDRALAB-II
I / SANDS / SANTOSS May August 2007
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Outline

• Background
• Objectives
• Conditions
• Instrumentation set-up
• Experimental Results
• Discussion Future work

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Background

• Existing sand transport models are primarily
  based on oscillatory flow tunnel experiments
• Former experiments indicate that flow differences
  between full scale surface waves and OFTs may
  have a substantial effect on sand transport

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Objectives

• Insight in sand transport processes and rates
  under full scale surface waves
• (-gt emphasize on sheet-flow conditions)
• Perform high resolution velocity, concentration
  (and transport)
• measurements under full scale, non-breaking,
  surface waves
• inside the wave boundary layer and free stream
• inside the sheet-flow layer and suspended
  sediment

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Conditions
Large wave flume (GWK) Coastal Research Centre
(FZK), Germany

• 300m long, 5m wide and 7m deep
• Regular, non-breaking, waves
• H 0.71.5 m T 5.09.1 s
• (Jonswap spectrum)
• Uniform quartz sand, D50 245 µm
• Water depth 3.50 m

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Waves in GWK H 1.5 m T 5.0 s Wave gauges
along the right (and left) side of the flume
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Conditions
Depth flume 7000 mm Depth water 3500 mm Wave
height 1500 mm Wave boundary layer 50
mm Sheet flow layer 10 - 15 mm
? under sheet-flow conditions gt90 of the sand is
transported inside the sheet-flow layer
Z 1100
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Instrumentation set-up
CCM-tankBuried in the sand bed to measure
sediment concentrations close to the bed.
Vertical position of the CCMs can be controlled
with sub-mm accuracy.
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Flow velocity measurements UVP, vectrino,
EMF Sediment concentrations measurements ABS,
TSS, CCM, UHCM Other Ripple profiler, pressure
sensor, wave gauges, bed profiler
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ABS TSS Time-averaged Concentration H 1.5 m,
T 6.5 s
Concentrations measured with Acoustic Backscatter
sensors (ABS 3 sensors 1, 2, 4 MHz) (solid
lines) and 5 suction tubes (dots).
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Time-averaged Concentration H 1.5 m, T 6.5 s
ABS TSS
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Z 6 mm
Upper sheet flow layer
Z 0 mm
Pick up layer
Z -1 mm
Z -4 mm
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UVP Net horizontal velocities H 1.5 m, T
6.5 s
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Net velocities x Concentration profile
X
After Ribberink et al. 2000 Dohmen-Janssen
Hanes, 2002
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Current related sediment flux
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Current related sediment flux
AOFT Delta flume experiments 2006
GWK experiments 2007
Schretlen et al., 2007
New full scale surface wave experiments give
insight in wave boundary layer velocities From
first results it appears that velocity behaviour
under surface waves differs from boundary layer
flows in oscillatory flow tunnels
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Discussion

• Current related sediment flux in relation to wave
  related flux
• Sand transport rates
• Further analyses of
• Flow velocity results (hor. ver.)
• sediment concentration measurements
• -gt both for suspension and sheet-flow layer
• sand transport measurements

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Future work

• Compare findings to oscillatory flow tunnels
• GWK experiments 2008 (alternative sediment)
• Ripple regime
• other SANTOSS activities

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Upper sheet flow layer
Sheet flow layer
Still bed level
Pick up layer
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Horizontal velocities (m/s)
Vertical velocities (m/s)
onshore
offshore

• Ensemble averaged over 50 waves
• Measured at 8 different levels above the bed (z
  in mm)
• The original still-bed level is located at z 0
  mm

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Future work

• Velocities
• UVP (4x)
• Vectrino
• EMF (4x)
• CCMs (cross correlation)
• Concentrations
• CCMs (3x)
• TSS (5 suction tubes)
• UHCM
• ABS
• Transport rates
• Bed profiles
• Fluxes (velocity concentration data)
• Wave height shape along the flume
• Development of the bed (cross shore profile)