Modellierung von Sedimenttransporten im Wattenmeer

- Gerold Brink-Spalink -

Forschergruppe BioGeoChemie des Watts TP 4

Gerold Brink-Spalink Jörg-Olaf Wolff Emil Stanev

BioGeoChemistry of Tidal Flats (SP 4)

Modelling Mud and Sand Transport in the East-Frisian Wadden Sea

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

Study Area: Spiekeroog Island

Spiekeroog

Otzumer Balje

Model Area: East Frisian Wadden Sea

7 Basins

Volume High Water: 184 Mio m³

Volume Low Water: 39 Mio m³

Area: 71 Mio m²

Inlet width: 2500 m

Inlet area: 11000 m²

Spiekeroog Basin:(spring tide)

Maximum channel depth: 12 m

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

uA

z

uA

zxg

z

uwfv

y

uv

x

u

t

uHV

22

vA

z

vA

zyg

z

vwfu

y

v

x

uv

t

vHV

22

Hydrodynamic Model (GETM)

0

z

w

y

v

x

u

Momentum equations:

Vertical mixing:

1tVA

,2

4

kct

k and from k--turbulence-model

,,1minmin

min

DD

DD

crit

Drying:

critDD for 1

critminfor 10 DDD

minfor 0 DD

•3D-model

•horizontal resolution: 200 m

•vertical resolution: D/10 (D=water depth)

•vertical grid: -coordinates

•Time discretization: mode splitting

• t1=3s for sea level, vert. integr. Velocities

• t2=15s for 3D-fields: turbulent variables, ...)

Hydrodynamic Model

Sediment Transport Model

erosiondeposition

settlingdiffusionadvection

EDcvzz

cA

zz

cw

y

cv

x

cu

t

csV

Deposition: d

dsb vcD

0

0 1

Erosion:e

eeME

0

0 1

Settling velocity:2

0

0

18d

gvs

sm

ss ckv or

(Sand) (Mud)

• 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 model is initialized half a tide after

hydrodynamic model

Forcing on northern boundary:

Boundary conditions:

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

Mean bottom shear velocity

Maximum bottom shear velocity

Duration of erosion of mud (top) and sand (bottom) during one spring tide cycle in percent:

u*=1,4 cm/s

u*=2,0 cm/s

Hydrodynamic conditions for erosion

flood

high water

ebb

low water

Integrated suspended sediment concentration

Sediment movements after 3 tidal cycles

Model estimate of sediment types:

Measurement of sand content in sediment:

250-125 µm 125-63 µm

Time evolution of vertical concentration profiles

Vertical average of concentration: Transport through inlet:

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. Conclusions

Overview:

1. Model Area: East Frisian Wadden Sea

2. Sediment Transport Model

3. Model Results

4. 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

Conclusions: