Quest4D Workshop Sediment Dynamics and Increasing Anthropogenic Pressure: Ways Forward? Flanders Hydraulics Research, May 14 th , 2009 Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM http:// www.mumm.ac.be/ Sediment Transport Modelling Belgian part of the North Sea Dries Van den Eynde, Michael Fettweis, Fritz Francken, Vera Van Lancker Management Unit of the North Sea Mathematical Models Jaak Monbaliu, Erik Toorman Katholieke Universiteit Leuven Job Janssens, Joris Vanlede, Toon Verwaest Flanders Hydraulics Research
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Quest4D Workshop Sediment Dynamics and Increasing Anthropogenic Pressure: Ways Forward? Flanders Hydraulics Research, May 14 th, 2009 Management Unit of.
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Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Sediment Transport ModellingBelgian part of the North Sea
Dries Van den Eynde, Michael Fettweis, Fritz Francken, Vera Van LanckerManagement Unit of the North Sea Mathematical Models
Jaak Monbaliu, Erik ToormanKatholieke Universiteit Leuven
Job Janssens, Joris Vanlede, Toon Verwaest Flanders Hydraulics Research
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Overview Two sediment transport models
– Transport of material in suspension MU-STM– Transport of sand MU-SEDIM
New developments– Bottom model– Flocculation model
Conclusions
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Sediment transport model mu-STM Semi-Lagrangian model – based on Second Moment
Method Bottom stress under influence of currents and waves Erosion and sedimentation Consolidation model with different layers in the bottom Boundary conditions
Applications– Dispersion of dumped material – optimisation of dredging
works– Sediment balance for the Belgian Continental Shelf
Turbidity maximum is a natural phenomenon not caused by the dumping Most of the material that enters the BCS from the Dover Strait,
disappears to the North
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Sediment transport model MU-SEDIM Bottom stress as function of currents and waves: Bijker formula Bottom roughness
– Skin-friction, roughness by bottom load, roughness by bottom ripples
Shields-criterium for start of sediment transport Different formulae for local total load
– Ackers-White (1973) with adaptations of Swart (1976, 1977) many different formulae available, results vary of orders of
magnitude Continuity for bottom: erosion and sedimentation
Applications– Modelling of volumetric changes of Kwintebank, assess effects of
sand extraction– Modelling sediment transport at wind mill farms
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Q4D Sediment transport model
MU-STM MU-SEDIM
Multi-classesFlocculation
model
Bed modelGeological information
Armouring Sand/mud layers
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Fall velocity of flocs
p : density of primary particles grain size analysis, OM, CaCO3 of SPM sample (2580 kg/m³)
•Critical shear stress measurement: 0.5-4Pa (top), 4-9 Pa (rest)•Bulk density: 1.3-1.6 g/cm³(carried out by Westrich & Jancke, Stuttgart Univ.)
Fluid mud on top, sandy with shell fragments; very soft mud with intercalation of sand layers
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Bed model: parent bed – active bed
In order to incorporate erosion of old sediments the bed is split in active & parent partActive layer: consist of different sub-layers to allow consolidation of mud, pore filling of sand by mud and segregation between sand/mud layers
Cohesive sediments (fine, mixed)•Active bed layers: ce < 4 Pa, sedimentation/erosion processes, corresponds to recent sediments•Parent bed layer: ce > 4 Pa, only erosion processes, corresponds to old sediments (Holocene, tertiary clays near surface)
Sandy sedimentsactive & passive layers
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Bed model - variables
Erosion characteristics: ce at surface ce averaged over the depth interval• Density averaged over the depth interval• Mass over the depth interval• Critical erosion rate averaged over the depth interval
Maps are constructed based on geological constraints and erosion flume experiments
2.6 2.8 3 3.2 3.4
51.1
51.2
51.3
51.4
51.5
51.6
Vers afgezet slib <1.0 N /m ²
W einig/m iddelm . gecons. s lib 1.4 N /m ²< <2.0 N /m ²
cr
cr
Recent mud ce <4PaCompact mud ce > 4Pa
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Bed model - variables
Sediment characteristics:• 8 grain size classes from gravel to clay• Clay is defined as fraction <8 µm is based on the difference
between sortable silts and aggregated particles (Chang et al., 2007)• Cohesive – non cohesive behaviour is based on Van Ledden et al.
(2004) adapted according to clay definition
Maps are constructed based on sedimentological data
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM
http://www.mumm.ac.be/
Bed model - ternary diagram
Most sediments fall into
I : non cohesive sand dominated
II : cohesive mixed sediments
III : non-cohesive mixed sediments
IV : cohesive clay dominated
Van Ledden et al. (2004)
Silt content [0.008<%<0.063mm]
0
10
20
30
40
50
60
70
80
90
100
Clay content [%<0.008mm]
0
10
20
30
40
50
60
70
80
90
100
Sand content
0102030405060708090100
IV
VI
VIII
II
I
40%
50%
Quest4D WorkshopSediment Dynamics and Increasing Anthropogenic Pressure: Ways
Forward?Flanders Hydraulics Research, May 14th, 2009
Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM