Hans Burchard 1 , Henk M. Schuttelaars 2 , an d Rockwell W. Geyer 3

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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*

description

Resi dual sediment fluxes in weakly-to-periodically stratified estuaries and tidal inlets* . Hans Burchard 1 , Henk M. Schuttelaars 2 , an d Rockwell W. Geyer 3 1. Leibniz Institute for Baltic Sea Research Warnemünde , Germany 2. TU Delft, The Netherlands - PowerPoint PPT Presentation

Transcript of Hans Burchard 1 , Henk M. Schuttelaars 2 , an d Rockwell W. Geyer 3

Page 1: Hans Burchard 1 ,  Henk  M. Schuttelaars 2 ,  an d Rockwell W. Geyer 3

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

floo

d-to

-ebb

tran

sitio

n

Stro

nger

floo

d

Shor

t floo

d-to

-ebb

tran

sitio

n

Stro

nger

ebb

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Stro

nger

floo

d

Long

floo

d-to

-ebb

tran

sitio

nSh

ort fl

ood-

to-e

bb tr

ansit

ion

Stro

nger

ebb

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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?