Hans Burchard 1 , Henk M. Schuttelaars 2 , an d Rockwell W. Geyer 3
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Transcript of Hans Burchard 1 , Henk M. Schuttelaars 2 , an d Rockwell W. Geyer 3
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Hans Burchard1, Henk M. Schuttelaars2, and Rockwell W. Geyer3
1. Leibniz Institute for Baltic Sea Research Warnemünde, Germany
2. TU Delft, The Netherlands3. Woods Hole Oceanographic Institute, MA, USA
*) J. Phys. Oceanogr., under review.
Residual sediment fluxes in weakly-to-periodically stratified
estuaries and tidal inlets*
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Question:
What are the processes driving residual sediment fluxes into the Wadden Sea?
Velocity and sediment profile data from Spiekeroog 2011
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MacCready & Geyer (2010) after Jay & Musiak (1994)
Longitudinal density gradients & tidal oscillations lead to:
Tidal straining
Residual velocity
Flood sediment Ebb sediment
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Observations of tidal pumping
Scully & Friedrichs (2007)
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Simpson number
Key non-dimensional numbers
Rouse number
Horizontal buoyancy gradientWater depthBottom friction velocity scale
Settling velocity
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Estuaries and tidal inlets
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Analytical solution of most simple setting:Stationary exhange flow with parabolic eddy mixing
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Analytical solution of most simple setting:Sediment fluxes in the Si – Ro parameter space
seaward
landwardHow does this compare to asymmetric tidal forcing?
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Approach = GOTM
unlimited bottom pool limited bottom pool no bottom pool
Define time scale for bottom sediment pool:
Te = Time needed to empty bottom pool at mean bed stress
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Effect of Si on bed stress
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Decomposition of sediment flux
fluctuation flux
transport flux
total flux
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Tidally averaged profiles
unlimited bottom pool limited bottom pool no bottom pool
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total flux fluctuation flux transport flux
unlim
ited
botto
m p
ool
no b
otto
m p
ool
Sediment flux in parameter space
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Adding an M4 tidal forcing component
Long flood-to-ebb transition
Short flood-to-ebb transition
Stronger flood
Stronger ebb
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Adding an M4 tidal forcing component
Long flood-to-ebb transition Stronger flood
Short flood-to-ebb transition Stronger ebb
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Long
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Stro
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Shor
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tran
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Stro
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Stro
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Long
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ansit
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Campaign in Lister Deep (April 2008)
Becherer et al. (GRL 2011)
shoals
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Becherer et al. (GRL 2011)
Campaign in Lister Deep (April 2008)
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d
Campaign in Lister Deep (April 2008)
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Conclusions for PACE
• Classical picture of estuarine sediment transport: transport flux dominates.
• Observations of Scully and Friedrichs indicate important role of tidal pumping (=fluctuation flux).
• The present study supports this.
• When high ammounts of sediment are available, then fluctution flux is dominant.
• The M4 phasing (and probably other higher harmonics) determines whether net sediment flux is landward or seaward.
• Since sediment flux depends on so many parameters, it may actually be unpredictable?