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Orientation of Outer Deltas

Orientation of Outer Deltas. Why are outer deltas formed? What determines the orientation (of the channels) of the outer delta + their dynamics?. ALW - 05/04/2002. Orientation of the Outer Delta :. Conceptual model:. Updrift: Downdrift: wave-dominated. Tide-dominated

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Orientation of Outer Deltas

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  1. Orientation of Outer Deltas • Why are outer deltas formed? • What determines the orientation (of the channels) of the outer delta + their dynamics? ALW - 05/04/2002

  2. Orientation of the Outer Delta: Conceptual model: • Updrift: • Downdrift: wave-dominated • Tide-dominated • Interaction shore parallel current • and current in the strait • Preferred sediment deposition • on downdrift side

  3. Sediment flux Hypothesis: • Asymmetry due to ‘external’ asymmetry only. • Hence the asymmetry in back-barrier area + alignment of islands not considered. Proposition: outer deltas are downdrift oriented w.r.t. the ‘large scale’ sediment flux

  4. From process-based models + observations M2 amplitude M2 phase

  5. M4 amplitude M4 phase M0 amplitude M0 amplitude

  6. Model Setup: Parameters varied: • M2 amplitude (default = 1 m) + phase • M4 amplitude (default = 0 m) + phase • M0 amplitude (default = 0 m) • initial bed profile (default = flat)

  7. M2 Amplitude Z2=1 Z2=1 Z2=-0.4 Z2=1 Z2=-1 Z2=1

  8. Df2 = 40 deg Z2=1 Z2=1 M2 Phase

  9. Z0=0 Z0=-0.1 Z0=0 Z0=0.1 Default: Z2_l = 0.9 Z2_r = 1.0 Df2 = 40 deg Influence of M0

  10. Influence of M4 phase (1) Z4=0.2 F4=290 Df4 = 60 deg Z4=0.2 F4=350 FD ED FD FD ED

  11. Influence of M4 phase (2) Z4=0.2 F4=110 Df4 = 60 deg Z4=0.2 F4=170 FD ED FD ED

  12. Z0=0 Z0=-0.1 Z0=0 Z0=0.1 Initial bed not flat

  13. M0 amplitude Comparison with data Relative phase UD DD UD UD DD+UD FD UD DD UD UD DD+UD ED : updrift (UD) FD: downdrift (DD) ED: updrift (UD) : downdrift (DD) However: M0 seems to be more ‘efficient’

  14. Conclusion • Orientation of outer deltas is downdrift with respect to sediment flux • Correlates well with the Wadden Sea embayments • Initial topography changes details, not overall picture

  15. Future work • Add waves • Influence of shape of embayment and width of throat

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