Hans Burchard 1 , Henk M. Schuttelaars 2 , and Rockwell W. Geyer 3 1. Leibniz Institute for Baltic Sea Research Warnemünde, Germany 2. TU Delft, The Netherlands 3. 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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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*
Question:
What are the processes driving
residual sediment fluxes into the Wadden Sea?
Velocity and sediment profile data from Spiekeroog 2011
MacCready & Geyer (2010) after Jay & Musiak (1994)
Longitudinal density gradients & tidal oscillations lead to:
Tidal straining
Residual velocity
Flood sediment Ebb sediment
Observations of tidal pumping
Scully & Friedrichs (2007)
Simpson number
Key non-dimensional numbers
Rouse number
Horizontal buoyancy gradientWater depthBottom friction velocity scale
Settling velocity
Estuaries and tidal inlets
Analytical solution of most simple setting:
Stationary exhange flow with parabolic eddy mixing
Analytical solution of most simple setting:
Sediment fluxes in the Si – Ro parameter space
seaward
landwardHow does this compare to asymmetric tidal forcing?
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
Effect of Si on bed stress
Decomposition of sediment flux
fluctuation flux
transport flux
total flux
Tidally averaged profiles
unlimited bottom pool limited bottom pool no bottom pool
total flux fluctuation flux transport flux
un
limit
ed
bott
om
pool
no b
ott
om
pool
Sediment flux in parameter space
Adding an M4 tidal forcing component
Long flood-to-ebb transition
Short flood-to-ebb transition
Stronger flood
Stronger ebb
Adding an M4 tidal forcing component
Long flood-to-ebb transition Stronger flood
Short flood-to-ebb transition Stronger ebb
Long fl
ood-t
o-e
bb t
ransi
tion
Str
onger
flood
Short
flood-t
o-e
bb t
ransi
tion
Str
onger
ebb
Str
onger
flood
Long fl
ood-t
o-e
bb t
ransi
tion
Short
flood-t
o-e
bb t
ransi
tion
Str
onger
ebb
Campaign in Lister Deep (April 2008)
Becherer et al. (GRL 2011)
shoals
Becherer et al. (GRL 2011)
Campaign in Lister Deep (April 2008)
d
Campaign in Lister Deep (April 2008)
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?
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