Presentation by Mijke van Oorschot (University of Utrecht) at the Delft3D User Days, during Delft Software Days 2016. Wednesday 2 November 2016, Delft.

1. Modelling invasive species in river systems:
interaction with native ecosystem engineers
and effects on morphodynamic processes
Mijke van Oorschot
Maarten Kleinhans, Gertjan Geerling,
Hans Middelkoop, Rob Leuven, Gregory Egger

2. Patterns in vegetation
Patterns
Allier river, France
Patterns in fluvial morphology

3. Eco-engineering effect of vegetation
Vegetation
Hydrology River morphologySediment balance

4. Vegetation
Hydrology River morphologySediment balance
Eco-engineering effect of vegetation
Interaction
creates dynamic
patterns
0
250
500
750
1000
1250
1500
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Discharge(cubicm/s)
mean minimum maximum
Period 1968 - 2000
River morphologySediment balance

5. Modeling vegetation – morphology
interactions
What is the long-term effect of dynamic vegetation on the
morphodynamics and vegetation pattern of a meandering river?
Static vegetation uniformly sown
Crosato & Saleh, 2011
Nicholas, 2013

6. Vegetation model
Riparian vegetation
Morphodynamics
Colonization
Sedimentation &
Erosion
Development Mortality
Flow (regime) Bed level
Interactively coupled
Matlab
Delft3D-
flow

7. Colonization
Sedimentation &
Erosion
Development Mortality
Flow (regime) Bed level
Morphodynamics
Vegetation
Hydraulic resistance
New substrate
Burial
Scour
Uprooting
Flooding
DesiccationColonisation
location
Vegetation model

8. Vegetation processes
Colonisation
1. Colonisation window
2. Water levels during dispersal period
Lowest water level
Highest water level
Bare substrate
Interaction & Mortality
Ecological time steps
Year + 1

9. Vegetation processes
Changing characteristics over time
Age Age Age
Shoot (m) Root (m) Frontal area (m)
Interaction
Year + 1
Colonisation

10. Vegetation processes
Changing characteristics over time
Chezy roughness
by Baptist
Frontal area Vegetation size
Interaction
Year + 1
Colonisation

11. Vegetation processes
Slope
Threshold
Flooding (days)
Desiccation (days)
Flow velocity (m/s)
Mortality
(%)
Interaction & Mortality
Year + 1
Colonisation

12. Vegetation processes
Flooding (days)
Desiccation (days)
Flow velocity (m/s)
Mortality
(%)
Sensitive
Resistant
Burial : sedimentation > shoot height
Scour: erosion > rooting depth
Different at each age
and life-stage!!
Interaction & Mortality
Year + 1
Colonisation
Van Oorschot, M., Kleinhans, M., Geerling, G., Middelkoop, H., 2016. Distinct patterns of interaction between
vegetation and morphodynamics. Earth Surface Processes and Landforms 41, 791–808.

13. 1. Without vegetation
2. Static vegetation (uniform, no growth, no mortality)
3. Dynamic vegetation (riparian trees)
4. Invasive species (riparian trees + invasive herb)
5. Human pressures (climate change, dams)
Model runs

14. Model result
Dynamic vegetation patterns, aging,
sustained dynamic meandering, distinct
patterns in river morphology

15. Chute cut-offs
Oxbows
Flow
Comparison to aerial photos
500 m

16. Comparison to aerial photos
Young Old
Young
Old
%Cover
Empirical
Data
Dynamic
Stripes
Areas
Dots

17. Synthesis dynamic vegetation
Dynamic vegetation; settling, growth and
mortality, creates natural biogeomorphological
patterns

18. Invasive species
What is the long-term effect of an invasive riparian plant
on native vegetation community and river morphology?
Fallopia japonica (Japanese Knotweed)

19. Invasive species
• No invaders
• Dense invaders (‘aggressive’)
– High fraction in cell
• Sparse invaders (‘mild’)
– Low fraction in cell

20. Invasive species results
Movies bed level plus vegetation
Aggressive invaders
Mild invaders

21. Results invasive species
No invaders Mild invader Aggressive invader
• Mild invader facilitates native vegetation
• Aggressive invader constrains native vegetation
Effect on native vegetation cover

22. Results invasive species
Center cell
Edge cell
Neighbour cell
Morphodynamic effects
Invader inclusion =
larger vegetation patches
Aggressive invader
Mild invader
No invader

23. Aggressive invader
Mild invader
No invader
Results invasive species
Morphodynamic effects
• Shielding by vegetation patches
• Invader inclusion = more native colonization in center
and edge of cell
Where do
native
seedlings
colonize?
Aggressive invaderMild invaderNo invader

24. Synthesis invasive species
Invasive and native species interact
through morphodynamic processes

25. Dams: work in progress
• Modified upstream discharge boundary to
simulate 2 dam operating scenarios

26. Dams: results vegetation
Construction dam
• Stabilization dam: aging vegetation, reduction colonization peaks
• Reversed dam: initial aging, reduction colonization peaks and
total reduction of vegetation

27. Dams: results habitat suitability
Post-processing
How are other riverine species affected by dams?
Salmon
Pike
Helophytes &
Macrophytes
Bivalves

28. Dams: results habitat suitability
Delft3D
Model
results
Statistics
Post-processing
run
HABITAT
model
Salmon
Pike
Helophytes &
Macrophytes
Matlab
Python
scripting
HSI
results
Year +1
Bivalves

29. Dams: results habitat suitability
Post-processing
• Dams decrease good habitat of fish
• Reversed dam increases good habitat water plants
• Stabile dam decreases good habitat water plants

30. Conclusions
• We can model the dynamic interaction between vegetation and river
morphodynamics
• Settling, growth and mortality of vegetation creates natural
biogeomorphological patterns and continuous dynamic meandering
• Invasive and native species interact through morphodynamic
processes
• Working on dam effects, dam removal, climate change, estuarine
species and interaction with mud
Mijke.vanoorschot@deltares.nl
Thank You!
Van Oorschot, et al., 2016. Distinct patterns of interaction
between vegetation and morphodynamics. ESPL 41, 791–808.
Come see me during the
breaks at my stand 