Sediment transport and underwater light climate affected by flexible aquatic vegetation

1. Sediment transport and underwater
light climate affected by flexible
aquatic vegetation
Jasper T. Dijkstra (Deltares, TU Delft)
Marieke M. van Katwijk (Radboud University Nijmegen)

2. Why?
7 augustus 2015
• Aquatic plants are important.
• There occurrence depends on feedback mechanisms.
• For aquatic plants, light=life.
• Flexibility –reconfiguration- matters for flow and sediment
transport.
• Approach:
• modelling flexibility,
• compare against field observations,
• study light climate for different vegetation scenarios.

3. Flexibility
Rigid
Flexible
Prone

4. Modelling: the principles
Plant properties
Dynveg Look-up table
Hydrodynamic conditions
Delft3DSediment properties Sediment transport, light conditions

5. Dynveg
1DV flow interaction between flow and flexible vegetation
• plant drag depends on orientation in flow; dynamic feedback
• k-epsilon turbulence model
• real plant properties (buoyancy, elasticity)
• can be coupled to Delft3D for 2/3D

6. Modelling: validation (1)
Experiments by Ed Morris et al. (2008, L&O) on Zostera noltii

7. The field experiment
Thanks to: MNHN, Shore

8. Modelling: validation (2)
Vegetation properties for range of flow conditions > Dynveg.
Feedback loop to vegetation position and CD (from Dynveg) every 5
minutes

9. Modelling: validation (2)
Veg Non-veg

10. Comparing 4 scenarios
Real vegetation
Dense vegetation
No vegetation
Stiff vegetation

11. Comparing the sediment transport

12. Modelling the light climate

 Kz
b sI I e
  0 f f c cK K K c K c

13. Conclusions
Not only vegetation presence, but also vegetation properties are
important for sediment transport and light climate.
Flexibility matters indeed.
In deep water, plants have more effect on bed load transport than on
suspended sediments.
The presence of plants extends their ‘depth limit’ for occurrence to
deeper waters.
Models like these are an important tool for modelling habitat suitability
and landscape development.