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DSD-INT 2019 Elbe Estuary Modelling Case Studies-Stanev


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Presentation by Emil Stanev (HZG Institute of Coastal Research, Germany), at the DANUBIUS Modelling Workshop, during Delft Software Days - Edition 2019. Friday, 8 November 2019, Delft.

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DSD-INT 2019 Elbe Estuary Modelling Case Studies-Stanev

  1. 1. Elbe Estuary. Modelling Case Studies Emil V. Stanev DANUBIUS Modelling Workshop Friday, 08 November 2019, Delft, The Netherlands (Elbe Delta)
  2. 2. Motivation 1. Share knowledge and experience about the modelling of river-sea systems. 2. Consider possible research-support when solving society-relevant issues, climate change and environmental protection Focus on 1. What happens when the river water encounters the sea water? 2. Nesting and seamless approach; coupling different modules Outline 1. Introduction 2. SCHISM 3. SED3D 4. WWM 5. ECOSMO
  3. 3. 1. Introduction (challenges) The water cycle Global European Seas J.P. Peixoto & A.H. Oort, Physics of Climate, 1992 Stanev and Lu (2013)
  4. 4. Chl-a µg/l Remote Sensing & FerryBox Data 1°E 2°E 3°E 4°E 5°E 6°E 7°E 8°E 54°N 52°N FerryBox Sediment dynamics and biogeochemical processes W. Schröder, personal communication
  5. 5. W. Schröder, personal communication Vertical mixing: a fundamental ingredient of coastal models
  6. 6. Where the river meets the sea Different estuaries and mixing processes • How is the "salt balance" maintained in an estuary? • Why does the river water not simply flush out all the salt and turn the estuary into fresh water? Strongly, partially mixed, salt wedge estuaries
  7. 7. Hansen & Rattray, (J. Marine Research, 23, 104-122; 1965) CD is the friction parameter, UT is the amplitude of the depth-averaged tidal velocity, ω is the tidal frequency, No = (βgsocean/H)1/2 is the buoyancy frequency, H is the depth, UR is the velocity of river flow, ß= 7.7 × 10-4 is the coefficient of salinity contraction, and g is the gravitational acceleration. M2 = CDUT 2/(ωNo H2) Estuarine classification Geyer and MacCready (Annu. Rev. Fluid Mech. 2014. 46:175–97) M2 = CDUT 2/(ωNo H2) quantifies the effectiveness of tidal mixing measuring the ratio of the tidal timescale to the vertical mixing timescale. Frf = UR/(ßgsoceanH)1/2, freshwater Froude number measuring the ratio between the net velocity due to river flow and the maximum frontal propagation speed No H.
  8. 8. Hydrology HD-Modell 2. The model GCOAST Modelling system Waves WAM Atmosphere COSMO-CCLM Ocean NEMO/SCHISM Biogeochemistry ECOSMO/E2E Atm. Chemistry CMAQ Marine chemistry MECOSMO Bio- accumulation Drift Models Coupler OASIS SPM
  9. 9. 3D, primitive equations, unstructured-grid. - Upgrade from an existing model (SELFE, A Semi-implicit Eulerian-Lagrangian Finite Element model for cross-scale ocean circulation). - Uses hybrid finite element and finite volume approach. - New viscosity formulation (effectively filters out spurious modes without introducing excessive dissipation). Semi-implicit Cross-scale Hydroscience Integrated System Model; - New higher-order implicit advection scheme for transport (TVD2) is proposed to effectively handle a wide range of Courant numbers - Addition of quadrangular elements into the model - Flexible vertical grid system (Zhang et al. 2015, OM) - Model polymorphism that unifies 1D/2DH/2DV/3D cells in a single model grid. Zhang Y.J., F. Ye, E. V. Stanev, and S. Grashorn (2016, Ocean Modelling).
  10. 10. Stanev et al. (2019, CSR)
  11. 11. 3. SPM dynamics • A zone within which the suspended sediment concentrations are higher than those in the river or further down in the estuary. • The turbidity maximum occurs more often in well-mixed and partially-mixed estuaries, and less often in stratified estuaries. • In many places the turbidity maximum contains more sediment than brought by rivers.
  12. 12. SED 3D
  13. 13. Stanev et al. (CSR, 2019)
  14. 14. 4. Wind waves. WWM III and ist coupling with SCHISM -WWM III (third generation spectral wave model) is described by Roland et al. (2012). -Wind input and dissipation is as in Bidlot et al. (2002). -SCHISM gets from WWM III the radiation stress. -The coupling between the wind-wave and the circulation model is made through the friction velocity computed from the wave model (Bertin et al., 2015). -The source terms for depth-induced wave breaking and bottom friction are computed as explained by Bertin et al. (2015). Schloen et al. (2017, OMOD)
  15. 15. Model validation Wind speed and significant wave height in July 2013 The meteorological situation and wind waves Observed and simulated significant wave height, direction and peak period
  16. 16. Left: Spatial and temporal variability of difference between salinity simulated in experiment RWF and RF: Consequent snapshots during one tidal period are shown for 23-24.07. Velocity-difference vectors are also plotted. Right: Time versus distance diagram along a section line north of the islands. (a) The ratio of significant wave height and tidal range averaged along the transect line north of the islands. (b) Wind speed and direction along the section line. (c) Difference of the u-component between experiment RWF and RF. Temporal-spatial variability
  17. 17. (a) The ratio of significant wave height and tidal range averaged for the whole model run and for a period with high waves (23 Jul 2011). (b) Vertical profile of difference in salinity on transect along the tidal channel for RWF and RF averaged over 16 tidal M2-periods. Estuarine implications
  18. 18. Results - Density gradients in the coastal zone reduce the tidal current by 18 %. - Wind waves enhance the circulation in some cases. The latter happens when strong winds blow resulting in long-shore currents following the western Dutch coast and the German Wadden Sea islands. - The wave-induced transport of salt leads to changes in the horizontal salinity distribution, which are very pronounced in regions of fresh water influence. - The weak stratification dominating the patterns of salinity in the coastal zone is mostly destroyed by wind waves. Thus, effects created by wind waves tend to substantially modify the estuarine circulation. - More extended description of the results can be found in Schloen et al. (2017).
  19. 19. WGE 5. BGC modelling Elbe model coupled hydrodynamically to bigger set-up (GB), atmospheric forcing by DWD data, river discharge, nutrient and plankton load from observations
  20. 20. 22 Ecological module: ECOSMO2 – a pelagic NPZD model plus bottom pool of nutrients Coupler: FABM (Bruggeman & Bolding, 2014) linking hydrodynamics and ecology ELBE BGC-MODELLING SYSTEM Set-up characteristcs: 33k horizontal nodes, 20 s-layers, TVD² transport, KL-turbulence model. ECOSMO/ MAECS/ SPM FABM Daewel & Schrum, 2013 Schrum et al., 2006
  21. 21. The M-2 amplitudes BGC properties Pein et al. (under revision)
  22. 22. (a) (b) (c)
  23. 23. (c) (e) (g) (a) (d) (f) (h) (b)log (Ri) Lateral processes
  24. 24. Conclusions Coastal ocean modelling is nowadays mature enough to address practical issues from coastal engineering, search and rescue, BGC, green energy, coastal management, response to climate change