Sediment transport and underwater

light climate affected by flexible

aquatic vegetation

Jasper T. Dijkstra (Deltares, TU Delft)

Marieke M. van Katwijk (Radboud University Nijmegen)

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.

Flexibility

Rigid

Flexible

Prone

Modelling: the principles

Plant properties

Dynveg Look-up table

Hydrodynamic conditions

Delft3D Sediment properties Sediment transport, light conditions

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

Modelling: validation (1)

Experiments by Ed Morris et al. (2008, L&O) on Zostera noltii

The field experiment

Thanks to: MNHN, Shore

Modelling: validation (2)

Vegetation properties for range of flow conditions > Dynveg.

Feedback loop to vegetation position and CD (from Dynveg) every 5

minutes

Modelling: validation (2)

Veg Non-veg

Comparing 4 scenarios

Real vegetation

Dense vegetation

No vegetation

Stiff vegetation

Comparing the sediment transport

Modelling the light climate

Kzb sI I e

0 f f c cK K K c K c

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.