Presentation by Roy van Weerdenburg and Bas van Maren (Deltares, Netherlands), at the Delft3D User Days, during Delft Software Days - Edition 2022. Tuesday, 15 November 2022.

1. Unifying the formulations and combining the best of both
Roy van Weerdenburg and Bas van Maren
Delft3D User Days 2022
Fine sediment transport modelling in
D-Morphology or D-Water Quality?

2. Fine sediment transport modelling in D-Morphology or D-Water Quality?
Within the Delft3D FM Suite, transport of fine sediment can be computed
within two different modules
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?
2
D-Morphology
online coupling
e.g. when modelling mud (or sand-mud)
morphodynamics or when density
coupling is important
D-Water Quality
online and offline (file-based) coupling
e.g. when modelling turbidity and effects
on water quality
e.g. What is the best module to answer the (research) questions?
e.g. What is available from previous projects?
Choose one of the modules based on content and/or practical matters

3. Fine sediment transport modelling in D-Morphology or D-Water Quality?
3
e.g. What is the best module to answer the (research) questions?
e.g. What is available from previous projects?
Choose one of the modules based on content and/or practical matters
What do we need to know before we convert fine sediment transport
models from D-Morphology to D-Water Quality and vice versa?
And what was needed to align these two modules a bit better?
~
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

4. What is actually different between D-Morphology or D-Water Quality?
• D-Water Quality (online coupling) and D-Morphology use the same advection-diffusion solver
(adopted from D-Flow FM module of the Delft3D FM Suite)
• Units!
• Transport formulations are similar, but slightly different
4
In case of a file-based coupling to D-Water Quality,
also the advection-diffusion solver is different
Buffer model (Van Kessel et al., 2011)
As the hydrodynamic model is the same,
vertical mixing and settling are the same
in D-Water Quality and D-Morphology
Differences arise at the water-bed
interface and in the bed
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

5. Differences at the water-bed interface
5
Buffer model (Van Kessel et al., 2011)
Deposition
(no differences)
Fractional deposition towards layer S2:
,
cr,depo
1
i s i i
D w C


 
= −
 
 
 
( )
,1 ,
1
i s i i
D w C

= −
,2 ,
i s i i
D w C

=
, ,
cr,i
1
i WAQ i WAQ
E M


 
= −
 
 
 
( )
, , cr,i
i MOR i MOR
E M  
= −
,
,
cr,1
i WAQ
i MOR
M
M

=
Resuspension from layer S1 (E1)
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

6. Differences at the water-bed interface
6
Buffer model (Van Kessel et al., 2011)
Resuspension from layer S2 (E2)
1.5
,2, ,2 ,2,
, ,2
1
i WAQ i i WAQ
cr i
E f M


 
= −
 
 
 
1
,2, ,2 ,2,
, ,2
1
i MOR i i MOR
cr i
E f M


 
= −
 
 
 
n: user-defined power function for the dimensionless excess bed shear stress
,2 ,2
,2
2 2
(1-n )
i i
i
sand sand
m m
f
d m

= =
In D-Water Quality, the buffer layer has
a fixed thickness and represents a
passive sand layer in which fines
infiltrate.
In D-Morphology, the buffer layer is
dynamic in thickness as the amount of
sand in this layer may vary in time.
,2
,2
i
i
sand mud
m
f
m +
=
Conceptual difference:
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

7. Application in a schematized tidal inlet
7
Set up models with fine sediment transport in D-Morphology
and D-Water Quality (both online and file-based coupling)
• 2DH (depth-averaged)
• Local wind waves (D-Waves coupling)
• One mud fraction (ws = 0.5 mm/s)
• No initial bed sediment; Initial sediment concentration is 1 g/L
• Concentration at offshore boundary is 5 mg/L
We provided a mass of sand in D-Morphology which corresponds to the
thickness of the buffer layer (d2) and switched off sand transport, to
mimic the immobile sand fraction in the buffer layer in D-Water Quality.
→ Compare results from different modules based on the net
result of deposition and resuspension.
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

8. Model results
8
Differences ~5% of total mass
More resuspension from buffer layer in
D-Water Quality, and therefore more
deposition at intertidal area in both layers
D-Morphology D-Water Quality D-Water Quality – D-Morphology
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

9. Model results
9
Differences ~5% of total mass
More resuspension from buffer layer in
D-Water Quality, and therefore more
deposition at intertidal area in both layers
,2 ,2
,2
2 2
(1-n )
i i
i
sand sand
m m
f
d m

= =
,2
,2
i
i
sand mud
m
f
m +
=
D-Morphology D-Water Quality
! Mud fraction in D-Water Quality
increases faster than in D-Morphology
We built a D-Water Quality research version to correct for this conceptual difference
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

10. Model results
10
D-Morphology D-Water Quality D-Water Quality – D-Morphology
Remaining differences ~1% of total mass
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

11. D-Water Quality: Online vs Offline (file based) coupling
11
Same process formulations, but different advection-diffusion solver
Communication at time step level (~ 1 min) in online coupling, every 30 minutes in offline coupling
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

12. D-Water Quality: Online vs Offline (file based) coupling
12
online coupling offline coupling offline - online
∆t = 1 min
Convergence OK:
time step more relevant than different
numerical solver
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

13. Computation times
13
1 year simulation time:
D-Flow FM (Hydrodynamics) 100
D-Flow FM + D-Morphology (one mud and one sand fraction) 130
D-Flow FM + D-Water Quality (online coupling; one mud fraction) 106
D-Water Quality (file-based coupling; one mud fraction) 3
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

14. Key message and outlook
14
Approach in a research project in the Ems-Dollard
estuary:
1. Spin-up period of multiple years for spatially
varying sediment composition in D-Water Quality
(file-based coupling)
2. Continue with modelling morphodynamic effects
of interventions in D-Morphology
Schrijvershof et al. (in prep.)
What do we need to know before we convert fine
sediment transport models from D-Morphology to
D-Water Quality and vice versa?
1. Mind the details in the implementation,
but differences in results are small
2. Significant differences in computation
times!
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?

15. Final remarks
15
Want to know more?
Roy.vanWeerdenburg@deltares.nl
Fine
sediment
transport
modelling
in
D-Morphology
or
D-Water
Quality?