Presentation by Lonneke Roelofs, University of Utrecht, The Netherlands, at the Delft3D and XBeach User Day: Coastal morphodynamics, during Delft Software Days - Edition 2019. Wednesday, 13 November 2019, Delft.

1. Faculty of Geosciences
River and delta morphodynamics
Morphodynamic effects of peat
compaction in a fluvial-tidal basin
A case of sinking natural levees
Lonneke Roelofs MSc
Marcio Boechat-Albernaz MSc, dr. Harm Jan Pierik, prof. dr. Maarten Kleinhans
dr. Sanneke van Asselen, dr. Helena van der Vegt, dr. ir. Bert Jagers,
Aulia Valencia MSc

2. Combination of two projects
Levee morphology and evolution in the fluvial-
tidal realm
MSc thesis – Numerical modelling & fieldwork
Peat compaction and delta evolution, a case
study on natural levees & crevasses
Internship Deltares – Numerical modelling

3. Levees

4. Peat compaction
Berendsen, 2005
Van Asselen, 2010

5. Case study: Oude Rijn
From tidal to fluvial
Levees played a role in closing
Well preserved due to peat
>0 m
<-2 m
Height
w.r.t. NAP

6. Numerical modelling
Delft3D
Water depth
(m)
• 4 sand fractions
• 1 silt fraction
• 1 clay fraction

7. Numerical modelling
Peat compaction
Model by Van Asselen (2010)
Peat thickness and organic content (LOI)
Peat thickness
Natural strain
Primary compaction
(stress)
Secondary compaction
(time)

8. Numerical modelling
Water depth
(m)

9. Results without compaction

10. Results without compaction
2
0
-2
-4
-6
-8
-10
Elevation(m)
SandSiltClay
Tidal amp
0.25 m
River Q
700 m³/s

11. SandSiltClay
Tidal amp
0.25 m
River Q
700 m³/s

12. General development
Q constant
No tide
Q variable
No tide
Q constant
Small tide
Q constant
Large tide
10
5
0
Distance(km)
10
5
0
Distance(km)
0 5 10 15 20
Distance (km)
0 5 10 15 20
Distance (km)

13. Peat
Overbank
Point bar
Channel belt
Older dep.
Grain size
C14

14. Results with compaction

15. Increasingpeatthickness
Elevation (m) Deposition (m)

16. Increasingpeatthickness

18. Discussion
Tides largely influence levee morphology, and
evolution
Increase width & height -> effective distribution
Crevasses
Peat compaction increases levee thickness and
crevasse length
Balance between compaction & sedimentation
important for development

19. Discussion
Adding compaction to Delft3D gives insight in
Evolution of levee morphology in compaction prone
environments
Influence of compaction on formation and evolution of
crevasse channels in peat rich environments
Further developments needed
Peat growth
■ The entrainment of sediments in peat deposits
■ The suffocation of peat vegetation
Dynamic system -> avulsions