Presentation by Thijs van Kessel (Deltares) and Joris Vanlede (Flanders Hydraulic Research), at the Delft3D - User Days (Day 4: Water quality and ecology), during Delft Software Days - Edition 2018. Thursday, 15 November 2018, Delft.

1. Delft3D User Days 2018
Mud dynamics in the Scheldt estuary
Modelling natural dynamics and human
interventions
Joris Vanlede (Flanders Hydraulics Research)
Thijs van Kessel (Deltares)

2. The Scheldt estuary
- At the border between the Netherlands and Belgium
- Important for accessibility to harbours (e.g. Antwerp)
- Safety issues (e.g. high water levels during storm surges)
- Important ecological functions
- Long-term collaborative research and management between the
Netherlands and Flanders (part of bi-lateral treaty)
- Present work is part of this project

3. Mud dynamics in the Scheldt Estuary
- Natural mud dynamics
- Suspended sediment concentration
- Turbidity, turbidity maximum
- Deposition rate on mud flats and in secondary channels
- Anthropogenic influence on mud dynamics
- Channel deepening
- Harbour construction
- Maintenance dredging and release of mud
- Land reclamations (past) and setbacks (future)

4. Trinity
Observations
Models
Understanding

5. NEVLA Model
NEderland – VLAanderen
Model of the Belgian part of the North Sea, Western Scheldt, Sea
Scheldt and tributaries
3D version (Triwaq) -> now used primarily in combination with
DELWAQ for cohesive sediment transport
2D version (Waqua) -> used for operational forecasting, updated
through Baseline
2D version (Delft3D 4 Suite) -> used for sand transport and morphology
Recent update of the 3D version with 2014/2015 bathy and validation
run 2014

6. Model grid
NEVLA

7. Model grid: Terneuzen
Resolution ~100m

8. Model grid: DGD
Resolution ~50m

9. Hydrodynamic model: Water Levels

10. Hydrodynamic model: Water Levels

11. Hydrodynamic model: Salinity

12. Mud modelling concepts
- 2L bed module (buffer concept)
- Aimed at long term (multiple years) and large scale (whole estuary)
- Modelling of suspended sediment and bed composition

13. Mud Balance
Sink: burial of alluvial sediments
Fluvial import
Marine Import
Export
Source: erosion of
exposed legacy
sediments
dm/dt = Fi + Mi – Ex + Erls – Bu ≠ 0
Inspired by Wartel, Van Eck, Van Maldegem
.
..
.
.
.

14. Model results on mud dynamics
Wal D. van der, T. van Kessel,
M.A. Eleveld, J. Vanlede (2010).
Spatial heterogeneity in estuarine
mud dynamics. . Ocean
Dynamics doi:10.1007/s10236-
010-0271-9.
Kessel, T. van, J. Vanlede, J.M.
de Kok (2011). Development of a
mud transport model for the
Scheldt estuary.
Continental Shelf Research 31
S165–S181 DOI:
10.1016/j.csr.2010.12.006.

15. Salinity and SPM along thalweg

16. Time series at Buoy 84 (recalibrated)

17. Mud balance (recalibrated)

18. Impacts of tidal dock and river discharge
Question:
Are high SSC levels in 2011
explained by low river discharge
or overdue maintenance dredging?

19. Impact reduced upstream discharge
Note: Dredging-dumping process
in Delft3D-WAQ enabled

20. Impact of reduced intervention level DGD
Note: Dredging-dumping process
in Delft3D-WAQ enabled

21. Impact DGD (previous work)
With DGD Without DGD
>2/3 of mud is
second-hand!

22. Conclusions
• Model available that reproduces the main features of large scale
and long term hydro- and mud dynamics in the Scheldt estuary
• Model has been applied to quantify natural and antropogenic
effects such as freshwater discharge variations, dock construction
and maintenance dredging
• SSC peak in 2011 caused by sediment pulse from overdue
maintenance,
• SSC peak in 2011 not caused by low freshwater discharge
• Anthropogenic influence on mud dynamics in Scheldt is substantial
• Points of attention:
• Validation of dynamic mud stocks (more data required)
• Intra-tidal dynamics underestimated