Physical Processes Associated with Onshore Ebb Shoal Migration

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Physical Processes Associated with Onshore Ebb
Shoal Migration
Nigel Aird Institute of Marine Studies
University of Plymouth
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Presentation Outline

• PhD - current focus
• May-2003 fieldwork program description and
  preliminary results
• Future work

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PhD - Current Focus

• What?
• A detailed study of the short term processes
  (hours to days) that lead to onshore ebb shoal
  migration

e.g. wave/tide driven mean currents, tidal
asymmetry, oscillatory currents, wave
skewness

• Why?
• These processes are important in the
  morphological evolution of natural beaches and
  are not well understood (Hoefel Elgar, 2003)

• How?
• Detailed analysis of field measurements

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Onshore Migration at TeignmouthAn Historic
Example
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Onshore Migration at Teignmouth A Recent Example
Animation not included
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May-2003 Fieldwork Program

• Dates
• 12/05/03 - 30/05/03
• Equipment
• Nearshore x2 Slots EMCM, PT, OBS
• Offshore x2 ADCPs
• Land Meteorology station speed
• Other Real time kinematic GPS survey,
  theodolite

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May-2003 Morphology and Instrument Locations
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Fieldwork - Conditions
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Preliminary ResultsWaves Currents
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Preliminary ResultsTransport Rates Spectra
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Summary (low energy conditions)

• Majority of sediment transport occurs in the surf
  zone

• Oscillatory component - sediment is predominantly
  suspended at infragravity frequencies

• Onshore directed (u-c in phase, also positive
  skewness)
• Small contribution to net transport

• Mean component gtgt oscillatory component

• Occurs on flood tide only (tidal asymmetry)
• Onshore directed

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Future Work

• Further analysis

• May 03 data set Slot 1b, 2a, 2b

• Nov/Dec 02 data set

• Modelling (MIKE21)

• Argus images

• Volume changes

• Onshore migration rates