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: