Modellierung von Sedimenttransporten im Wattenmeer

1. Modelling Mud and Sand Transport in the East-Frisian Wadden Sea Modellierung von Sedimenttransporten im Wattenmeer - Gerold Brink-Spalink - Gerold Brink-Spalink Jörg-Olaf Wolff Emil Stanev Forschergruppe BioGeoChemie des Watts BioGeoChemistry of Tidal Flats (SP 4) TP 4

2. Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions • Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions

3. Spiekeroog Otzumer Balje Study Area: Spiekeroog Island

4. Model Area: East Frisian Wadden Sea 7 Basins Spiekeroog Basin: (spring tide) Volume High Water: 184 Mio m³ Volume Low Water: 39 Mio m³ Area: 71 Mio m² Inlet width: 2500 m Inlet area: 11000 m² Maximum channel depth: 12 m

5. Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions • Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions

6. Vertical mixing: Drying: k and e from k-e-turbulence-model Hydrodynamic Model (GETM) Momentum equations:

7. Hydrodynamic Model • 3D-model • horizontal resolution: 200 m • vertical resolution: D/10 (D=water depth) • vertical grid: s-coordinates • Time discretization: mode splitting • Dt1=3s for sea level, vert. integr. Velocities • Dt2=15s for 3D-fields: turbulent variables, ...)

8. Settling velocity: or (Sand) (Mud) Deposition: Erosion: Sediment Transport Model

9. Forcing on northern boundary: Boundary conditions: • Sediment on ground (Sand: 100µm, Mud) unlimited • Morphologic changes during model run are not considered in topography data • Water flowing into model area carries no sediment • Sediment flowing out of model area is „lost“ • Sediment modelis initialized half a tide after hydrodynamic model

10. Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions • Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions

11. Mean bottom shear velocity Duration of erosion of mud (top) and sand (bottom) during one spring tide cycle in percent: u*=1,4 cm/s Maximum bottom shear velocity u*=2,0 cm/s Hydrodynamic conditions for erosion

12. Integrated suspended sediment concentration flood high water ebb low water

15. Sediment movements after 3 tidal cycles

16. Measurement of sand content in sediment: 250-125 µm 125-63 µm Model estimate of sediment types:

17. Time evolution of vertical concentration profiles

18. Measured concentration: Vertical average of concentration: Transport through inlet:

19. Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions • Overview: • Model Area: East Frisian Wadden Sea • Sediment Transport Model • Model Results • Conclusions

20. Conclusions: • A 3D-model for sediment transport has been set up, that accounts for the main processes (erosion, settling, deposition, advection, turbulent mixing) • Suspended sediment concentration patterns show consistent behaviour with observations • Spatial distribution of sediment types matches observations in large areas • Further calibration with measurements necessary • Waves need to be taken into account