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DSD-INT 2018 Mud dynamics in the Scheldt estuary - modelling natural dynamics and human interventions - van Kessel

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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.

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DSD-INT 2018 Mud dynamics in the Scheldt estuary - modelling natural dynamics and human interventions - van Kessel

  1. 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. 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. 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. 4. Trinity Observations Models Understanding
  5. 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. 6. Model grid NEVLA
  7. 7. Model grid: Terneuzen Resolution ~100m
  8. 8. Model grid: DGD Resolution ~50m
  9. 9. Hydrodynamic model: Water Levels
  10. 10. Hydrodynamic model: Water Levels
  11. 11. Hydrodynamic model: Salinity
  12. 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. 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. 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. 15. Salinity and SPM along thalweg
  16. 16. Time series at Buoy 84 (recalibrated)
  17. 17. Mud balance (recalibrated)
  18. 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. 19. Impact reduced upstream discharge Note: Dredging-dumping process in Delft3D-WAQ enabled
  20. 20. Impact of reduced intervention level DGD Note: Dredging-dumping process in Delft3D-WAQ enabled
  21. 21. Impact DGD (previous work) With DGD Without DGD >2/3 of mud is second-hand!
  22. 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

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