1. 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*

2. Question: What are the processes driving residual sediment fluxes into the Wadden Sea? Velocity and sediment profile data from Spiekeroog 2011

3. MacCready & Geyer (2010) after Jay & Musiak (1994) Longitudinal density gradients & tidal oscillations lead to: Tidal straining Residual velocity Flood sedimentEbb sediment

4. Observations of tidal pumping Scully & Frie drichs (2007)

5. Simpson number Key non-dimensional numbers Rouse number Horizontal buoyancy gradient Water depth Bottom friction velocity scale Settling velocity

6. Estuaries and tidal inlets

7. Analytical solution of most simple setting: Stationary exhange flow with parabolic eddy mixing

8. Analytical solution of most simple setting: Sediment fluxes in the Si – Ro parameter space seaward landward How does this compare to asymmetric tidal forcing?

9. Approach = GOTM unlimited bottom pool limited bottom poolno bottom pool Define time scale for bottom sediment pool: T e = Time needed to empty bottom pool at mean bed stress

10. Effect of Si on bed stress

11. Decomposition of sediment flux fluctuation flux transport flux total flux

12. Tidally averaged profiles unlimited bottom pool limited bottom poolno bottom pool

13. total fluxfluctuation fluxtransport flux unlimited bottom pool no bottom pool Sediment flux in parameter space

14. Adding an M 4 tidal forcing component Long flood-to-ebb transition Short flood-to-ebb transition Stronger flood Stronger ebb

15. Adding an M 4 tidal forcing component Long flood-to-ebb transition Stronger flood Short flood-to-ebb transition Stronger ebb

16. Long flood-to-ebb transition Stronger flood Short flood-to-ebb transition Stronger ebb

17. Stronger flood Long flood-to-ebb transition Short flood-to-ebb transition Stronger ebb

18. Campaign in Lister Deep (April 2008) Becherer et al. (GRL 2011) shoals

19. Becherer et al. (GRL 2011) Campaign in Lister Deep (April 2008)

20. d

21. 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 M 4 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?