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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 - PowerPoint PPT Presentation
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Orientation of Outer Deltas
ALW - 05/04/2002
•Why are outer deltas formed?•What determines the orientation (of the channels)
of the outer delta + their dynamics?
•Why are outer deltas formed?•What determines the orientation (of the channels)
of the outer delta + their dynamics?
Conceptual model: •Updrift:
•Downdrift: wave-dominated
•Tide-dominated•Interaction shore parallel current and current in the strait•Preferred sediment deposition on downdrift side
Orientation of the Outer Delta:
Proposition: outer deltas are downdrift oriented w.r.t. the ‘large scale’ sediment flux
Sediment flux
•Asymmetry due to ‘external’ asymmetry only.•Hence the asymmetry in back-barrier area + alignment of islands not considered.
Hypothesis:
From process-based models + observations
M2 amplitude M2 phase
M4 amplitude M4 phase
M0 amplitudeM0 amplitude
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)
M2 AmplitudeZ2=1 Z2=1 Z2=-0.4 Z2=1 Z2=-1 Z2=1
M2 Phase
degZ2=1 Z2=1
Influence of M0 Default: Z2_l = 0.9 Z2_r = 1.0 = 40 deg
Z0=0 Z0=-0.1 Z0=0 Z0=0.1
Influence of M4 phase (1)
FD
ED
FD
FD
ED
degZ4=0.2
Z4=0.2
Influence of M4 phase (2)
degZ4=0.2
Z4=0.2 FD
ED
FD
ED
Initial bed not flat
Z0=0 Z0=-0.1 Z0=0 Z0=0.1
Comparison with data
M0 amplitude Relative phase
FD
ED
: updrift (UD): downdrift (DD)
FD: downdrift (DD)ED: updrift (UD)
UD DD UD UD DD+UD
UD DD UD UD DD+UD
However: M0 seems to be more ‘efficient’
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
Future work
•Add waves•Influence of shape of embayment and width of throat