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
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Faculty of Geosciences
River and delta morphodynamics RGB
blue 0 101 164
green 0 166 81
yellow 255 212 0
Effects of fluvial mud supply on
large-scale estuarine morphology
L. Braat, M.G. Kleinhans, T. van Kessel
Introduction
Objective: effect of fluvial mud concentrations on
the large-scale shape and patterns of estuaries.
2
Introduction
3
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.
Method
2DH morphological model
Bed module for sand-mud mixtures (van Kessel
et al., 2012)
Scenarios fluvial mud input
Sensitivity analyses
Comparing data
4
Fluvial mud
concentration
[kg/m3]
0.01
0.005
0.001
0.0005
0
Initial conditions
Funnel-shaped idealised estuary
Initial flat bed
No mud
5
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
6
Results
7
Bathymetry
Sand
Bathymetry
Sand + mud
Mud deposits
Cross-section: Mudflats
8
Cross-section: Filling channel
9
Validation: Western Scheldt
10 McLaren 1994 Bathymetry
Mu
d f
raction
Scenarios
11
Narr
ow
er/
short
er
estu
aries
Narr
ow
er
channels
Incre
ase m
ud c
oncentr
ation
Hypsometry
12
[kg/m3]
Model runs Westerschelde
Morphodynamics (timestacks)
13
Sand and mud Sand
Upscaling dry cell erosion
14
Difference
Tidal-Morfac 30
Morfac 30
Upscaling dry cell erosion
15
morphological time
many timesteps
less timesteps
Conclusions
Large effect of fluvial mud on estuaries
Decrease estuary width
Decrease channel dimensions
Decrease dynamics
Issue with dry cell erosion
16
Future research
Expand the model (waves, current, marine mud,
salinity, 3D)
More validation with field data
Transverse bed slope effect
17
Questions?
18
Extra slide - TiMORFAC
19
time
TiMORFAC
MORFAC
Tidal cycle
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
20
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
Upscaling dry cell erosion
21
dt
dt * MORFAC
Equal morphological time
dt TiMORFAC
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
22
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