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