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Physical Processes Associated with Onshore Ebb Shoal Migration

Physical Processes Associated with Onshore Ebb Shoal Migration. Nigel Aird Institute of Marine Studies University of Plymouth. Presentation Outline. PhD - current focus May-2003 fieldwork program description and preliminary results Future work. PhD - Current Focus. What?

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Physical Processes Associated with Onshore Ebb Shoal Migration

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

  2. Presentation Outline • PhD - current focus • May-2003 fieldwork program description and preliminary results • Future work

  3. 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

  4. 27th October 1988 27th April 1987 Photo collages courtesy of Syd Hook 19th February 1988 7th January 1988 23th October 1987 Onshore Migration at TeignmouthAn Historic Example

  5. Onshore Migration at Teignmouth A Recent Example Animation not included

  6. May-2003 Fieldwork Program • Dates: • 12/05/03 - 30/05/03 • Equipment: • Nearshore: x2 Slots: EMCM, PT, OBS • Offshore: x2 ADCP’s • Land: Meteorology station speed • Other: Real time kinematic GPS survey, theodolite

  7. May-2003 Morphology and Instrument Locations

  8. Fieldwork - Conditions

  9. Preliminary ResultsWaves & Currents

  10. Preliminary ResultsTransport Rates & Spectra

  11. 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 >> oscillatory component • Occurs on flood tide only (tidal asymmetry) • Onshore directed

  12. energetics 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

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