This document discusses a study investigating the effect of fluvial mud supply on large-scale estuarine morphology. The study uses a 2D morphological model with a bed module for sand-mud mixtures to simulate scenarios with different fluvial mud input concentrations. Results show that higher mud concentrations lead to narrower and shallower estuaries and channels with less dynamics. However, issues were discovered with the model's representation of dry cell erosion over long timescales. Future work is needed to expand the model and obtain more validation from field data.

1. Faculty of Geosciences
River and delta morphodynamics
Effects of fluvial mud supply on
large-scale estuarine morphology
L. Braat, M.G. Kleinhans, T. van Kessel

2. Introduction
Objective: effect of fluvial mud concentrations on
the large-scale shape and patterns of estuaries.
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3. Introduction
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Objective: effect of fluvial mud concentrations on
the large scale shape and patterns of estuaries.
Hypothesis: cohesive sediments reduce the
ability to erode, leading to narrower channels,
increase in channel depth, decrease dynamics,
less avulsions and therefore a lower braiding
index.

4. Method
2DH morphological model
Bed module for sand-mud mixtures (van Kessel
et al., 2012)
Scenarios fluvial mud input
Sensitivity analyses
Comparing data
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Fluvial mud
concentration
[kg/m3]
0.01
0.005
0.001
0.0005
0

5. Initial conditions
Funnel-shaped idealised estuary
Initial flat bed
No mud
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6. Boundary conditions
River
Total discharge boundary
Mud concentration
Sea along-shore
Water level boundary
Astronomic components
M2 of 1.5 m
Sea cross-shore
Neumann no gradient
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7. Results
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Bathymetry
Sand
Bathymetry
Sand + mud
Mud deposits

8. Cross-section: Mudflats
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9. Cross-section: Filling channel
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10. Validation: Western Scheldt
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McLaren 1994Bathymetry
Mudfraction

11. Scenarios
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Narrower/shorterestuaries
Narrowerchannels
Increasemudconcentration

12. Hypsometry
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[kg/m3]
Model runs Westerschelde

13. Morphodynamics (timestacks)
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Sand and mudSand

14. Upscaling dry cell erosion
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Difference
Tidal-Morfac 30
Morfac 30

15. Upscaling dry cell erosion
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morphological time
many timesteps
less timesteps

16. Conclusions
Large effect of fluvial mud on estuaries
Decrease estuary width
Decrease channel dimensions
Decrease dynamics
Issue with dry cell erosion
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17. Future research
Expand the model (waves, current, marine mud,
salinity, 3D)
More validation with field data
Transverse bed slope effect
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18. Questions?
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19. Extra slide - TiMORFAC
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time
TiMORFAC
MORFAC
Tidal cycle

20. Parameters
Mdf par. value
mnkmax 202 201 1
dt 0.2
ccofu /ccofv 65
Viscouv 1
dicouv 10
Tlfsmo 60
Pmcrit 0.3
Betam 3
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Mor par. value
RDC 0.01
RDW 0.02
MorFac 1000
MorStt 1440
Tresh 0.05
EqmBc True
DensIn False
AksFac 1
Rwave 2
AlfaBs 1
SedThr 0.05
ThetSD 0.5
Islope 3. Koch & Flokstra
Ashld 1
Bshld 0.5
Underlayer value
ThTrLyr 0.1
NEuLyr 10
ThLaLyr/ThEuLyr 0.2
IDiffusion 0
FluFFlyr 0
Sed par. value
SedDia (sand) 2e-4
WS0/WSM 2.5e-4
TcrSed 1e3
TcrEro 5e-1
EroPar 1e-4

21. Upscaling dry cell erosion
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dt
dt * MORFAC
Equal morphological time
dt TiMORFAC

22. Discussion
Sesitive to bedslope effect.
Should be set to extreme values with EH (van der
Wegen and Roelvink, 2012)
Concerns use Morfac
Simulation transport for longer tidal period
■  trial speedup factor over 1 tidal cycle
■ Discovered problem with dry cell erosion
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