Verbetering randvoorwaardenmodel DEELRAPPORT 5 ACTUALISATIE VAN HET 3D SCHELDEMODEL

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1 Verbetering randvoorwaardenmodel DEELRAPPORT 5 ACTUALISATIE VAN HET 3D SCHELDEMODEL 00_018 WL Rapporten

2 Verbetering randvoorwaardenmodel Deelrapport 5 Actualisatie van het 3D Scheldemodel Verheyen, B.; Vanlede, J.; Decrop, B.; Verwaest, T.; Mostaert, F. April 2013 WL2013R00_018_5rev2_0 I/RA/11382/12.152/VBA

3 This publication must be cited as follows: Verheyen, B.; Vanlede, J.; Decrop, B.; Verwaest, T.; Mostaert, F. (2013). Verbetering randvoorwaardenmodel: Deelrapport 5 Actualisatie van het 3D Scheldemodel. Version 2_0. WL Rapporten, 00_018. Flanders Hydraulics Research & IMDC: Antwerp, Belgium. Published by: In collaboration with: Waterbouwkundig Laboratorium Flanders Hydraulics Research B-2140 Antwerp Tel. +32 (0) Fax +32 (0) waterbouwkundiglabo@vlaanderen.be International Marine and Dredging Consultants nv Coveliersstraat 15 B-2600 Antwerpen Tel: +32 (0) Fax: +32 (0) Nothing from this publication may be duplicated and/or published by means of print, photocopy, microfilm or otherwise, without the written consent of the publisher.

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5 Contents 1. Introduction Units and reference plane Abbreviations Available data Water levels Flow Velocity Discharge Transects with ebb and flood discharge Salinity Methodology Model description The NEVLA model Bathymetry Boundary conditions Model parameters Actualization of the 3D Nevla model List of executed scenarios Model changes Model grid and bathymetry improvements Training walls: strek- and leidam Bathymetry Belgian Continental Shelf Initial conditions Discharge Merelbeke Model results Comparison to reference run (simg19) Annual run with the actualized model simg34 (year 2006) Conclusions and recommendations Conclusions Recommendations List of references Appendix A Definition of statistical parameters... A1 Appendix B Hypsometric curves... A4 Appendix C Tidal analysis... A8 Appendix D Discharges... A42 Appendix E Time series of stationary velocities... A47 Appendix F Time series of salinities... A54 Final version WL2013R00_018_5rev2_0 I

6 List of tables Table 4-1: Available stations with water level measurments for the year Table 4-2: Stationary velocity measurement Table 4-3: Overview available discharge data Table 4-4: Overview of available transects with ebb and flood discharges Table 4-5: Overview of available stations with salinity measurements Table 6-1: Layer distribution in the 3D Nevla model Table 7-1: Overview of executed scenarios Table 10-2: Model qualification for different RMAE ranges, based on Sutherland et al. (2003)... A3 Final version WL2013R00_018_5rev2_0 II

7 List of figures Figure 4-1: Available measurement locations Figure 4-2: Overview transects with ebb and flood discharges Figure 6-1: Grids of the overall ZUNO model (blue) and detailed NEVLA model (red) Figure 6-2: Grid domain NEVLA 3D model (simg19 and simg34) Figure 6-3: Bathymetry (mnap) NEVLA 3D model (simg34) Figure 6-4: Bottom roughness (in Manning) in the Nevla 3D model (simg34) Figure 7-1: Model grid adaptions for simg28 and simg34, compared to simg19, in Lower Sea Scheldt (upper) and Upper Sea Scheldt (lower) Figure 7-2: Model bathymetry near the training walls for simg19 (upper) and sisimg29 and simg34 (lower) Figure 7-3: Bathymetry of the BCS before the new interpolation (top) and after the new interpolation (below). Note the bad representation and transition in the western part of the BCS in the upper figure Figure 7-4: Difference in new and old bathymetry (positive values indicate a deeper new bathymetry). The figure clearly shows the discontinuous old bathymetry in the West and the bad interpolation of the sand banks Figure 7-5: Velocity field in the Dijle 15 minutes before the simulation crashes due to a too high velocity gradient Figure 7-6: Model grid in the section of the Dijle where the high velocity gradient occurred. Outer dike areas are clearly present in the model Figure 7-7: Bathymetry and discharge location at Merelbeke for simg Figure 7-8: Bathymetry and discharger location at Merelbeke for simg Figure 8-1: Analysis of modelled (simg19, simg34) and measured tidal component M2 for amplitude (upper) and phase (lower) Figure 8-2: Analysis of modelled (simg19, simg34) and measured amplitude of tidal components M4 (upper) and M6 (lower) Figure 8-3: RMSE between simg34 and simg19 of the complete timeseries of water level along the Scheldt estuary Figure 8-4: Calculated water level (simg19 and simg34) and measured water level in Schoonaarde. The new reference run (simg34) reproduces better the LW Figure 8-5: Velocity field of the old reference run (simg19) around the training walls. The current cannot pass over the training wall Figure 8-6: Velocity field of the new reference run (simg34) around the training walls. The current can pass over the training wall around high water Figure 8-7: Stationary velocities for simg19 and simg34 in BCS, Westhinder (upper) and Wandelaar (lower) Figure 8-8: Stationary velocities for simg19 and simg34 around training wall, downstream in Bath (upper) and between both training walls in Zandvliet (lower) Figure 8-9: Stationary velocities for simg19 and simg34 in Sea Scheldt, upstream training wall in the Lower Sea Scheldt in Antwerp (upper) and in the Upper Sea Scheldt in Schoonaarde (lower) Figure 8-10: Stationary velocities for simg19 and simg28 up to simg34 around the training walls, between both training walls in Zandvliet (upper), and just upstream in Boei 97 (lower) Figure 8-11: Modelled (simg19 and simg34) and measured discharges in the Western Scheldt over Gat van Ossenisse (upper) and Middelgat (lower) Figure 8-12: Modelled (simg19 and simg34) and measured discharges in the Lower Sea Scheldt, Oosterweel (upper) and the Upper Sea Scheldt, Schoonaarde (lower) Figure 8-13: Analysis of modelled (simg34) and measured tidal component M2 for amplitude (upper) and phase (lower) Final version WL2013R00_018_5rev2_0 III

8 Figure 8-14: Analysis of modelled (simg34) and measured properties of assymetry of vertical tide, amplitude ratio M4/M2 (upper) and phase shift 2M2-M4 (lower) Figure 8-15: Vector difference (simg34 versus measurements) of the 10 main components (Z0, M2, N2, S2, L2, MU2, K1, O1, M4, M6) for the different stations along the Scheldt estuary Figure 8-16: Low passed average error at Vlissingen of model results (simg34) minus measurements Figure 8-17: Modelled (simg34) and observed velocities in the BCS, Wandelaar (upper) and Bol van Heist (lower) Figure 8-18: Modelled (simg34) and observed velocities in the BCS, A2B Boei (MOW1) (upper) and in the Lower Sea Scheldt, Oosterweel (lower) Figure 8-19: Modelled (simg34) and observed salinities at the mouth of the Scheldt, Vlakte van de Raan (upper) and upstream in the Lower Sea Scheldt, Boei 84 (lower) Figure 10-1: Definition of straight and oblique setup (after Adema, 2006).... A1 Final version WL2013R00_018_5rev2_0 IV

9 1. Introduction In the framework of the project Verbetering randvoorwaardenmodel a constant maintenance and improvement of the NEVLA model is performed. This hydrodynamic model is designed with the SIMONA software and includes a large part of the BCS, the Scheldt estuary and all its tributaries which are tidally influenced. The NEVLA model is extensively used in research both internally and externally of Flanders Hydraulics Research, among which the LTV O&M projects considering the themes Veiligheid and Toegankelijkheid. Already a large effort has been done improving the performance of the depth averaged (2D) version of the NEVLA model. A sensitivity analysis and first calibration are described in Verbetering randvoorwaardenmodel Deelrapport 1: Gevoeligheidsanalyse (Vanlede et al., 2008a) and Verbetering randvoorwaardenmodel Deelrapport 2: Afregelen van het Scheldemodel (Vanlede et al., 2008b). Further detailed improvements were performed and can be found in Verbetering randvoorwaardenmodel Deelrapport 3: Kalibratie bovenlopen (Maximova et al., 2009a) and Verbetering randvoorwaardenmodel Deelrapport 4: Extra aanpassingen Zeeschelde (Maximova et al., 2009b). Future research will focus more on the 3D development of the NEVLA model. Previous 3D versions of the NEVLA model are described in van Kessel et al. (2008) and (2010) where the hydrodynamic output of the NEVLA model was used as a driving force for a mud transport model. The present document describes the developments in the NEVLA3D model with respect to the 3D model used in van Kessel et al. (2010). The model grid and bathymetry improvements made by FHR in 2009 in the 2D NEVLA model (Maximova et al, 2009a & 2009b) are integrated in the 3D NEVLA model. Furthermore, an update of the bathymetry of the BCS is performed, the discharge location and local bathymetry at Merelbeke have been changed and a new initial condition is applied. The hydrodynamic scenario used in van Kessel et al. (2010) (simg19) is used as reference run in the description. Run-ID s higher then simg19 represent consecutive changes, which resulted in the hydrodynamic scenario simg34. In simg34 the hydrodynamics of the year 2006 are calculated. The model settings (viscosity, roughness, time step) are not changed from simg19 to simg34. The actualized model simg34 is used for sediment transport calculations in van Kessel et al (2011). A new calibration of the roughness field for the 3D model is scheduled in 2012 at FHR (Vanlede et al., 2012 in preparation). Final version WL2013R00_018_5rev2_0 1

10 2. Units and reference plane Times are represented in MET. Depths, altitudes and water levels are represented in meters NAP. Depths are positive downwards and water levels are positive upwards. The horizontal coordinate system is RD Parijs. Final version WL2013R00_018_5rev2_0 2

11 3. Abbreviations ADCP amt BCS BMM DGD FHR HIC HMCZ HW KNMI LW MAE MET MVB MUMM NAP NEVLA RD Parijs RMAE RMSE RWS TAW Acoustic Doppler Current Profiler Afdeling Maritieme Toegang Belgian Continental Shelf Beheerseenheid van het Mathematisch Model van de Noordzee (zie ook MUMM) Deurganckdok Flanders Hydraulics Research Hydrologisch InformatieCentrum Hydro Meteo Centrum Zeeland High Water Koninklijk Nederlands Meteorologisch Instituut Low Water Mean absolute error Mean European Time Meetnet Vlaamse Banken Management Unit of the North Sea Mathematical Models and the Scheldt Estuary (zie ook BMM) Normaal Amsterdams Peil (vertical reference system) Nederlands-Vlaams waterbewegingsmodel Rijksdriehoekscoördinaten Parijs (horizontal reference system) Relative mean absolute error Root mean square error Rijkswaterstaat Tweede algemene waterpassing (vertical reference system) Final version WL2013R00_018_5rev2_0 3

12 4. Available data 4.1. Water levels For the year 2006, water level measurements are available at 48 stations with time-interval of 10 minutes, see Table 4-1. The locations of these stations are represented in Figure 4-1. The data are obtained from MVB, HMCZ and HIC. Table 4-1: Available stations with water level measurments for the year Nr Measuring station Data source 1. Antwerpen HIC 2. Antwerpen HMCZ 3. Appelzak (MOW2) MVB 4. Baalhoek HMCZ 5. Bath HMCZ 6. Bol Knokke MVB 7. Boom HIC 8. Borssele HMCZ 9. Boudewijnsluis HIC 10. Breskens HMCZ 11. Cadzand HMCZ 12. Dendermonde HIC 13. Duffel HIC 14. Emblem HIC 15. Hansweert HMCZ 16. Hemiksem HIC 17. Hombeek HIC 18. Kallo HIC 19. Kallo HMCZ 20. Kessel HIC 21. Liefkenshoek HMCZ 22. Liefkenshoek HIC 23. Lier Maasfort HIC 24. Lief Molbrug HIC 25. Mechelen stuw afwaarts HIC 26. Melle HIC 27. Nieuwpoort MVB Final version WL2013R00_018_5rev2_0 4

13 28. Oostende MVB 29. Overloop Hansweert HMCZ 30. Rijmenam HIC 31. Schaar Van De Noord HMCZ 32. Schelle HIC 33. Schoonaarde HIC 34. St Amands HIC 35. Temse HIC 36. Terneuzen HMCZ 37. Tielrode HIC 38. Vlakte Van De Raan HMCZ 39. Vlissingen HMCZ 40. Walem HIC 41. Walsoorden HMCZ 42. Wandelaar MVB 43. Westhinder MVB 44. Westkapelle HMCZ 45. Wetteren HIC 46. Zandvliet HIC 47. Zeebrugge MVB 48. Zemst HIC Final version WL2013R00_018_5rev2_0 5

14 Figure 4-1: Available measurement locations Flow Velocity Available stationary velocity measurements for the year 2006 are listed in Table 4-2. The location of the stations can be found in Figure 4-1. Table 4-2: Stationary velocity measurement. Nr Measuring station Data source Availability 1. Bol van Heist (MOW3) MVB 1/01/ /06/2006 & 3/07/2006 1/01/ Wandelaar MVB 1/01/2006 1/01/ Tripod deployment MOW1 (ADP) BMM 4. Tripod deployment Blankenberge (ADP) 5. A2B-boei (MOW1) IMDC 14/02/ /02/2006 & 15/05/ /06/2006 BMM 8/11/ /12/ /06/ /08/2006 & 1/09/ /11/2006 & 20/12/2006 1/01/2007 1/01/ /01/2006 & 6. Oosterweel IMDC 26/01/ /06/2006 & 29/06/ /08/2006 & 28/09/2006 1/01/ Boei 97 IMDC 20/12/2006 1/01/2007 Final version WL2013R00_018_5rev2_0 6

15 4.3. Discharge Upstream of the model 8 sources with discharges are imposed. Table 4-3 lists the data used for these boundary conditions. The location of the stations can be found in Figure 4-1. Table 4-3: Overview available discharge data. Nr Location Data source Data description 1. Scheldt Merelbeke HIC Measured daily averaged time series at Melle 2. Dender Dendermonde HIC Measured daily averaged time series at Appels 3. Zenne Zemst HIC Measured (Q-H) daily averaged time series at Eppegem 4. Dijle - Haacht HIC Measured (Q-H) daily averaged time series at Haacht 5. Grote Nete - Itegem HIC Measured (Q-H) daily averaged time series at Itegem 6. Kleine Nete - Grobbendonk HIC Measured (Q-H) daily averaged time series at Grobbendonk 7. Kanaal Gent-Terneuzen HIC Hourly values 8. Spuikanaal Bath RWS Zeeland 10 minute values 4.4. Transects with ebb and flood discharge Based on sailed ADCP transects, ebb and flood discharges are defined. These discharges represent a 13 hour measurement of one tidal cycle. Table 4-4 list all the available transects for which a 13 hour measurement is available. Figure 4-2 gives an overview of the location of the transects. Table 4-4: Overview of available transects with ebb and flood discharges. Nr Transect Data source 1. Raai 13: Oostgat-Deurloo-Wielingen RWS Zeeland 2. Raai 12: Wielingen-Deurloo-Oostgat RWS Zeeland 3. Raai 11: Wielingen-Sardijngeul RWS Zeeland 4. Raai 10: Vaarwater langs hoofdplaat Honte RWS Zeeland 5. Raai 9: Vaarwater langs hoofdplaat Honte/Schaar van Spijker RWS Zeeland 6. Raai 8: Pas van Terneuzen Everingen RWS Zeeland 7. Raai 7: Pas van Terneuzen Everingen RWS Zeeland 8. Raai 7a: Zuid Everingen RWS Zeeland 9. Raai 6: MIddelgat-Gat van Ossenisse RWS Zeeland 10. Raai 5: Zuidergat-Schaar van Waarde RWS Zeeland Final version WL2013R00_018_5rev2_0 7

16 11. Raai 3: Overloop van Valkenisse-Zimmermangeul RWS Zeeland 12. Raai 2: Schaar van de Noord RWS Zeeland 13. Raai 1: Vaarwater boven Bath-Ballastplaat RWS Zeeland 14. Liefkenshoek MONEOS 15. Oosterweel MONEOS 16. Kruikbeke MONEOS 17. Schoonaarde MONEOS 18. Boom MONEOS Figure 4-2: Overview transects with ebb and flood discharges. Final version WL2013R00_018_5rev2_0 8

17 4.5. Salinity Five stations with salinity data are available and are listed in Table 4-5. In every station two time series of salinities are present, one for the upper part of the water column and one for the lower part of the water column. The location of the stations can be found in Figure 4-2. Table 4-5: Overview of available stations with salinity measurements. Nr Measuring station Data source 1. Vlakte Van De Raan HMCZ 2. Hoofdplaat HMCZ 3. Baalhoek HMCZ 4. Boei 97 HMCZ 5. Boei 84 HMCZ Final version WL2013R00_018_5rev2_0 9

18 5. Methodology This chapter describes the methodology to analyze the model performance. Model and measurements are compared and analyzed using the MATLAB tool VIMM v2.7, developed at FHR. The following output is generated: - Tidal analysis of water levels (amplitudes and phases of constituents, vector difference). - Statistical evaluation of time series of water levels (Bias, RMSE, RMSE0) and of levels of HW and LW and time of HW and LW - Low pass averaged differential signal between model results and measurements - Time series of velocities and statistical evaluation (MAE, RMAE) of components and (BIAS, RMSE, RMSE0) of magnitude and direction of currents. - Time series of discharges and statistical evaluation (Bias, RMSE) of discharge. - Vectorplots representing the calculated velocity fields. The tidal analysis presented in this report is performed in MATLAB using t_tide, as developed by Pawlowicz et al. (2002). Amplitudes and phases are derived for the main tidal components M2, S2, O1, K1 and Z0 for comparison of simg19 with the actualized model. For the annual run of the actualized model the 10 main components are derived: Z0, M2, N2, S2, M4, L2, K1, MU2, M6, O1. Furthermore the model results are summarized in an overall error, the summed vector differences at a number of selected stations (Gerritsen et al., 2003) and (de Brye et al., 2010). This error includes the evaluation between model and observations for both the amplitude and phase of each harmonic component. Appendix A contains the mathematical expression of this analysis. The asymmetry of the vertical tide can be analyzed based upon the tidal components M2, M4 (Wang et al., 2002). The amplitude ratio M4/M2 describes the asymmetry of the vertical tide. The phase difference 2M2- M4 indicates the nature of the tidal asymmetry. If 2M2-M4 equals 0, there is no asymmetry in the system. A positive difference (0 to 180 ) means the duration of the ebb phase is longer than the duration of flood and thus maximum currents occur during flood (flood dominant). A negative value means the ebb phase is shorter and thus maximum currents occur during ebb (ebb dominant). Measured discharges over transects are available for specific through-tide measurements. To be able to use these measurements for analysis with model results, a comparable tide is searched in the modeled period. It is selected based on the smallest RMSE 0 value between the observed tides during the measurement and during the selected modeling period. Using these discharges over transect, flow through ebb and flood channels can be analyzed. Stationary velocity measurements are analyzed for the magnitude and direction of currents. Also an analysis of the components of the currents is performed based on Sutherland et al. (2003). This results in a MAE (mean absolute error), combining magnitude and direction, and a RMAE (relative mean absolute error), allowing to evaluate the performance of the model. Appendix A contains more details. Final version WL2013R00_018_5rev2_0 10

19 6. Model description This chapter gives a general description of the NEVLA hydrodynamical model, and focusses further on model version simg19, as used for sediment transport calculations in van Kessel et al. (2010). Model version simg19, is the reference simulation for the actualization discussed in chapter The NEVLA model The NEVLA (NEderlands-VLAams) model is a hydrodynamic model, designed in the SIMONA software. SIMONA (SImulatie MOdellen NAtte waterstaat) is a program developed by Rijkswaterstaat, for 2D (WAQUA module) and 3D (TRIWAQ module) modelling of water movement, particle dispersion and fluid mud transport and consists of a number of programs for preprocessing (preparation of simulations), computing and post processing (visualisation of the model results). The NEVLA model domain includes a large part of the BCS, the Scheldt estuary and all its tributaries which are tidal dependent, Durme, Rupel, Nete, Dijle and Zenne. Boundary conditions are imposed downstream and upstream. Upstream, measured discharges are imposed. For the downstream boundary conditions can be chosen between two set-ups. One set-up of downstream boundary condition is located at the mouth (Cadzand-Westkapelle) and is based on water level measurements. The other set-up is located offshore and based on nesting in the larger scale ZUNO model. The roughness field in the model is defined in Manning and is variable over the model domain. The model has active cells with maximal grid dimensions in M and N direction of 379 and 3000 cells. Figure 6-1 and Figure 6-2 present the model grid domain. The NEVLA model was primarily developed in depth averaged state (2D) and was calibrated and improved in different stages by Vanlede et al. (2008a en 2008b) and Maximova et al. (2009a en 2009b). Meanwhile, based on the work in Vanlede et al. (2008b), a 3D version of the NEVLA model was derived. The model is presented in van Kessel et al. (2008) and (2010). The 3D model also includes salinity. The model used in van Kessel et al. (2010), called simg19, is the reference simulation. This model will be described in the following paragraphs and the model changes discussed in chapter 7, are compared to simg19. The SIMONA version simona has been applied for the simulations Bathymetry The bathymetry of the NEVLA model simg19 is designed to represent the situation for the year 2006 and is more extensively prescribed in Vanlede et al. (2008). In the Upper Sea Scheldt surveys of 2001 were used (amt). The Rupel basin has been taken from the model M729_09 (Adema, 2006). The bathymetry in the Lower Sea Scheldt is based upon surveys of (Flemish Hydrography, Antwerp). Data for 2006 was used to create a bathymetry for the Western Scheldt, with the intertidal areas based on laser-altimetry surveys of 2003 (RWS-Zeeland). Also the area around the mouth is based upon surveys of 2003 (RWS Zeeland). The remaining bathymetry of the offshore Belgian and Dutch coastal area is made out of the bathymetry of the Kustzuid model version 5. Figure 6-3 presents the final bathymetry Boundary conditions At the North Sea boundary the model is coupled with the larger ZUNO-grof (Zuidelijke Noordzee) model, as shown in figure 6-1. The ZUNO model was run with time- and space varying wind. The two boundaries perpendicular to the coastline (east and west in Figure 6-1) are implemented as velocity boundaries. The boundary parallel to the coastline (north in Figure 6-1) is implemented as a Riemann boundary. The boundary conditions for the year 2006, obtained from the ZUNO model, were corrected for the phases of the components M4 and M6 by subtracting respectively 40 and 15, both for water levels and velocities. The ZUNO model (the finer grid version) is described in detail in Leyssen et al., Final version WL2013R00_018_5rev2_0 11

20 Upstream at Grobbendonk (Kleine Nete), Itegem (Grote Nete), Eppegem (Zenne), Haacht (Dijle), Dendermonde (Dender) en Merelbeke (Bovenschelde en Leie) measured daily median discharges were imposed. Also a discharge is imposed for the Bath canal and the canal Gent-Terneuzen. The measured wind direction and speed at Vlissingen (source: KNMI) for the year 2006 is uniformly imposed on the model domain Model parameters The bottom roughness field is defined by a space-varying Manning coefficient, as represented in figure 6-4. The roughness is prescribed in different zones throughout the model domain. The roughest zone is present between Bath and Zandvliet (0.028 m -1/3 s), the smoothest section occurs upstream of Sint-Amands (0.017 m -1/3 s). The model has 6 layers with a thickness, represented in table 6-1, in a quasi-logarithmic distribution, in which the upper layer is divided in two. This vertical distribution allows to represent enough vertical resolution close to the bottom and surface. The horizontal viscosity en diffusivity are constant and are respectively 1 m²/s and 10 m²/s. In the vertical, a k-ε turbulence model is applied. The time step is 7.5 seconds. Table 6-1: Layer distribution in the 3D Nevla model. Layer Thickness (% water column) 1 (surface) (bottom) 5 Final version WL2013R00_018_5rev2_0 12

21 Figure 6-1: Grids of the overall ZUNO model (blue) and detailed NEVLA model (red). Final version WL2013R00_018_5rev2_0 13

22 Figure 6-2: Grid domain NEVLA 3D model (simg19 and simg34). Final version WL2013R00_018_5rev2_0 14

23 Figure 6-3: Bathymetry (mnap) NEVLA 3D model (simg34). Final version WL2013R00_018_5rev2_0 15

24 Figure 6-4: Bottom roughness (in Manning) in the Nevla 3D model (simg34). Final version WL2013R00_018_5rev2_0 16

25 7. Actualization of the 3D Nevla model The following paragraphs describe the actualization of the existing 3D NEVLA model simg19. All changes are accumulated in the new reference run simg34. Therefore the different changes will be discussed by comparing simg34 with simg List of executed scenarios Table 7-1 lists the executed simulations. All six simulations (simg28 up to simg33) contain one or more improvements or model changes which have accumulated in a new reference run simg34. Also an extra simulation, simg35, has been done which represents a smaller period for comparison with the previous runs. Table 7-1: Overview of executed scenarios. Name Description Period simulation simg19 Reference run. 1/10/2006 8:00 1/01/2007 0:00 simg28 Adaptation of grid and bathymetry as reported in 1/10/2006 8:00 1/11/2006 8:00 Maximova et al. (2009). simg29 Strek- and leidam represented in the bathymetry, 1/10/2006 8:00 1/11/2006 8:00 previous thin dams removed. simg30 Bathymetry BCS actualized. 1/10/2006 8:00 1/11/2006 8:00 simg31 Check of numerical instability in Dijle, 5/01/2006 5:30 6/03/2006 5:30 New set of initial conditions. simg32 Location of discharge at Merelbeke and local 1/10/2006 8:00 1/11/2006 8:00 bathymetry changed. simg33 Check of discharge at Merelbeke during high 2/02/2006 0:00 20/02/2006 0:00 discharge. simg34 New reference run. 5/01/2006 5:30 5/01/2007 5:30 simg35 Similar to simg34 but with similar output period for comparisons. 1/10/2006 8:00 1/11/2006 8: Model changes In this paragraph the model changes in simg34 with respect to simg19 are discussed Model grid and bathymetry improvements The model grid adaptations reported in Maximova et al (2009a & 2009b) are integrated in the 3D hydrodynamic model. They include intertidal areas along the Sea Scheldt and its tributaries in the model grid. Most changes were implemented in the Upper Sea Scheldt (see figure 7-1). The Durme river was extended until its tidal border (figure 7-1). Also the numerical schematisation in the area of the Deurganckdok was refined. The total area of Deurganckdok was included in the model and a higher resolution was obtained. Together with the model grid improvements, the bathymetry of the calibrated model of Maximova et al. (2009b) is imposed. The bathymetry differs with simg19 in local bathymetrical changes in the Zenne and in the Upper Sea Scheldt. In Maximova et al., (2009a), a renewed gridcell averaging interpolation method was used. The bathymetry also contains the strek- and leidam near the Zandvliet - Berendrecht sluices (Maximova et al., 2009b). Appendix B contains the hypsometric curves and shows the change in volume storage between the bathymetries from simg19 and simg28 and further on. In the Western Scheldt nothing is changed. Although the grid has extended in simg28, the storage volume is decreased in the Sea Scheldt and the Rupel basin, also for the intertidal areas that are situated circa between -3mNAP and +4mNAP. Final version WL2013R00_018_5rev2_0 17

26 Figure 7-1: Model grid adaptions for simg28 and simg34, compared to simg19, in Lower Sea Scheldt (upper) and Upper Sea Scheldt (lower) Training walls: strek- and leidam Originally the training wall near the Zandvliet - Berendrecht sluices are represented as thin dams in the 3D model. Water cannot flow over these dams, in reality though, flow over the dams is possible beyond a certain water level between low and high water. Maximova et al (2009b) already removed the thin dams in the 2D model by adapting the bathymetry.based on the samples used by Decrop et al. (2010), a new interpolation is made of the bathymetry of the training wall, making sure the crest height is represented by Final version WL2013R00_018_5rev2_0 18

27 at least one cell. The thin dams are removed in the 3D model. Figure 7-2 presents the bathymetry of simg19 and simg34 near the training wall. Figure 7-2: Model bathymetry near the training walls for simg19 (upper) and sisimg29 and simg34 (lower) Bathymetry Belgian Continental Shelf The bathymetry in the Western part of the Belgian Continental Shelf (BCS) was based on samples with a coarse resolution (triple the grid resolution), which resulted in a poor interpolation of topographic features such as sandbanks. Furthermore the western part of the model was extended in a later phase without assuring a smooth transition between the existing bathymetry and the new interpolated part. Final version WL2013R00_018_5rev2_0 19

28 Samples of the BCS (2007, Afdeling Kust) with a resolution of 25m were used to create a new bathymetry of the BCS (Figure 4.4). Attention has been paid that the transition between the existing bathymetry and the newly interpolated one is smoothly enough to avoid numerical spurious oscilation due to discontinuities in the transition. Figure 7-3 shows both bathymetries in the BCS and Figure 7-4 represents the difference between the new and old bathymetry. Furthermore a spike in the bathymetry around the Kallo sluice is removed. Figure 7-3: Bathymetry of the BCS before the new interpolation (top) and after the new interpolation (below). Note the bad representation and transition in the western part of the BCS in the upper figure. Final version WL2013R00_018_5rev2_0 20

29 Figure 7-4: Difference in new and old bathymetry (positive values indicate a deeper new bathymetry). The figure clearly shows the discontinuous old bathymetry in the West and the bad interpolation of the sand banks Initial conditions During the simulation of the year 2006, numerical instabilities (no convergence for the momentum solver) were discovered. A high velocity gradient was observed during a flood discharge in the Dijle. Due to the high imposed initial conditions (9 mnap for waterlevel), water was available on the dike s crest. With the high water level in the Dijle due to the flood discharge, this platform of water made contact with the river and a high local velocity gradient was observed. Figure 7-5 displays the velocity field 15 minutes before the model crashes, the contact with the platform was already made. Therefore a new initial condition was applied imposing a lower water level of 1.5 mnap downstream of Schelle and 3 mnap upstream of Sint- Amands and in the Zenne, Dijle and Nete. Furthermore the grid contains also outer dike areas, areas beyond the river bank s crest (figure 7-6). These areas don t have impact on the normal hydrodynamics in the river, but when wet due to a uniform initial condition, they can cause numerical instabilities. It is therefore recommended to remove these inactive cells from the model grid Discharge Merelbeke The discharge locations imposed in Maximova et al. (2009b) have been used. At Merelbeke, the discharge was imposed at the actual location of the weir. The model also contained the quay walls of the sluices. This lead locally to high velocities during high discharges. The bathymetry and discharge location were therefore changed locally to guarantee a smooth inflow. Figure 7-7 and figure 7-8 represent the old and new bathymetry and discharge at Merelbeke. Final version WL2013R00_018_5rev2_0 21

30 Figure 7-5: Velocity field in the Dijle 15 minutes before the simulation crashes due to a too high velocity gradient. Figure 7-6: Model grid in the section of the Dijle where the high velocity gradient occurred. Outer dike areas are clearly present in the model. Final version WL2013R00_018_5rev2_0 22

31 Figure 7-7: Bathymetry and discharge location at Merelbeke for simg19. Figure 7-8: Bathymetry and discharger location at Merelbeke for simg34. Final version WL2013R00_018_5rev2_0 23

32 8. Model results The results of the actualized 3D hydrodynamical model are presented in two parts. First, a comparison is made with the model results of the reference run simg19. This comparison is made for the last quarter of Secondly, the results of the actualized model simg34 are summarized for the entire year Comparison to reference run (simg19) A harmonic analysis for the water level M2 component shows a similar behavior for both simg19 and simg34 (figure 8-1). The average difference in amplitude M2 is about 1 cm. The phases of the two runs are nearly identical (difference smaller than 1 ). A greater difference between the two models becomes apparent when analyzing the higher harmonics (M4, M6), Figure 8-2. This difference is mainly due to the difference in implementation of the training wall near the Dutch-Belgian border, discussed in Section In simg19, these structures were implemented as impermeable thin dams. In simg34, these structures are implemented as obstacles in the model bathymetry that will flood above a certain water level. This results in a difference in amplitude of the higher harmonics upstream the Dutch-Belgian border, and has a possible impact on the modeled tidal asymmetry. The difference in M4 and M6 amplitude due to the different implementation of the training wall is around 1 cm. The difference in phase around Antwerp is 3 for M4 and 2 for M6. Comparing the water levels of simg19 and simg34 results in an overall RMSE (figure 8-3). The difference in calculated water levels is limited to 1 à 2 cm in the BCS and the Western Scheldt. At Bath the difference increases to 3 cm due to the removal of the thin dams, but at Zandvliet the difference lowers again to 2 cm. Further upstream the bathymetry of Maximova et al (2009b) has been used and the difference increases up to 4 cm, with a local larger effect that is only present in Schoonaarde (figure 8-4), and better represents the LW. The effect of the removal of the thin dams is shown in the velocity fields in figure 8-5 and figure 8-6. Currents around high water are more accurate in the new reference run. The change in the bathymetry of the BCS can locally be observed (for example in modeled velocities at Westhinder, figure 8-7). But outside this region, the effect of the bathymetrical change is limited (for example modeled velocities at Wandelaar in figure 8-7). The effect of the training walls is visible in the current at Bath, especially in Zandvliet where the peak velocities have tripled (figure 8-8). The effect on currents in Zandvliet is also not limited to the period around high water. The effect seems to work up to Antwerpen Loodsgebouw (figure 8-9). But comparison of simg28 (new bathymetry, thin dams) and simg29 (new bathymetry, no thin dams) indicates that the effect of the removal of the thin dams is very local (figure 8-10). The observed effect on the currents at Antwerpen must be due to the extended bathymetrical influence of the training wall and or due to the overall influence of the new bathymetry of Maximova et al. (2009b). Also the bathymetrical change in the Upper Sea Scheldt has an impact on the currents. This can be seen in for example Schoonaarde. Discharges in the Western Scheldt are the same between simg19 and simg34 (figure 8-11), but a decrease in discharge in the Sea Scheldt has been observed in simg34 (figure 8-12), which can be explained by the decrease in storage volume in intertidal areas (paragraph 7.2.1). Final version WL2013R00_018_5rev2_0 24

33 Figure 8-1: Analysis of modelled (simg19, simg34) and measured tidal component M2 for amplitude (upper) and phase (lower). Final version WL2013R00_018_5rev2_0 25

34 Figure 8-2: Analysis of modelled (simg19, simg34) and measured amplitude of tidal components M4 (upper) and M6 (lower). Final version WL2013R00_018_5rev2_0 26

35 Figure 8-3: RMSE between simg34 and simg19 of the complete timeseries of water level along the Scheldt estuary. Figure 8-4: Calculated water level (simg19 and simg34) and measured water level in Schoonaarde. The new reference run (simg34) reproduces better the LW. Final version WL2013R00_018_5rev2_0 27

36 Figure 8-5: Velocity field of the old reference run (simg19) around the training walls. The current cannot pass over the training wall. Final version WL2013R00_018_5rev2_0 28

37 Figure 8-6: Velocity field of the new reference run (simg34) around the training walls. The current can pass over the training wall around high water. Final version WL2013R00_018_5rev2_0 29

38 Figure 8-7: Stationary velocities for simg19 and simg34 in BCS, Westhinder (upper) and Wandelaar (lower). Final version WL2013R00_018_5rev2_0 30

39 Figure 8-8: Stationary velocities for simg19 and simg34 around training wall, downstream in Bath (upper) and between both training walls in Zandvliet (lower). Final version WL2013R00_018_5rev2_0 31

40 Figure 8-9: Stationary velocities for simg19 and simg34 in Sea Scheldt, upstream training wall in the Lower Sea Scheldt in Antwerp (upper) and in the Upper Sea Scheldt in Schoonaarde (lower). Final version WL2013R00_018_5rev2_0 32

41 Figure 8-10: Stationary velocities for simg19 and simg28 up to simg34 around the training walls, between both training walls in Zandvliet (upper), and just upstream in Boei 97 (lower). Final version WL2013R00_018_5rev2_0 33

42 Figure 8-11: Modelled (simg19 and simg34) and measured discharges in the Western Scheldt over Gat van Ossenisse (upper) and Middelgat (lower). Final version WL2013R00_018_5rev2_0 34

43 Figure 8-12: Modelled (simg19 and simg34) and measured discharges in the Lower Sea Scheldt, Oosterweel (upper) and the Upper Sea Scheldt, Schoonaarde (lower). Final version WL2013R00_018_5rev2_0 35

44 8.2. Annual run with the actualized model simg34 (year 2006) The results of simg34 are discussed for the entire year Tidal components Figure 8-13 shows the computed and observed M2 amplitude as analysed for the entire year 2006, for different points along the estuary. M2 is the most important tidal component and contains most of the tidal energy. The model reproduces the combined effects of convergence of the estuary and friction. This is shown by the peak in amplitude around Schelle, which is visible in both measurements and model. The average difference in M2 amplitude between model and measurements is 4 cm. The difference varies between -4 cm (Antwerp, -2%) and +1 cm (BCS, +1%). The difference in M2 phase is smaller than 4. The phase difference 2M2-M4 and the amplitude ratio M4/M2 describe the asymmetry of the vertical tide (Wang, 2002). These parameters are well calculated in the Western Scheldt and Sea Scheldt as can be seen in figure A summary of the main tidal components based on measurements and model results are presented in Appendix C. The overall vector difference, based on the 10 main tidal components and over all available stations, is 0.78 m. Figure 8-15 represents the value for the stations in the BCS and the Scheldt. The value is smallest in the BCS and downstream the Western Scheldt and increases upstream in the Western Scheldt and in the Sea Scheldt where the tidal interaction becomes more complex. Water levels The Root Mean Square Error (RMSE) of computed water levels varies between 20 cm at sea to 30 cm at the upstream end of the model, at Ghent. This error is higher than the M2 amplitude difference, as other tidal components also contribute to the RMSE. In addition, the error in the non-tidal part of the water level curve plays a role, such as set-up or set-down by wind. This non-tidal part is mainly included in the boundary conditions. The RMSE on the high water and low water level are respectively 10 à 15 cm and 5 à 10 cm. HW and LW are on average 10 to 15 min later in the model. Error with low-pass filter Figure 8-16 shows the error between modeled and measured water levels at Vlissingen, passed through a low-pass Godin filter (Godin, 1972) in order to remove the tidal signal. What remains is the slowly varying part of the modeling error. It seems that the model overestimates the water level in the first part of the year, and under-estimates the water level in the last quarter. Such error may be expected as the model is steered at its downstream boundary by a train of different models (in this case the Continental Shelf Model and the Southern North Sea Model), and not by a time series of measured water levels. Leyssen et al. (2012) validated the larger scale ZUNOfijn, which is comparable to but not identical to the ZUNOgrof model this model simg34 is nested in. Analysis of the ZUNOfijn model for the year 2009 showed similar differences as the NEVLA model for the water levels and phases of the tidal components. Discharges Based on a comparable tide, the model is analysed for discharges over transects. Appendix D contains the results of modeled (simg34) and measured discharges. The RMSE value is 1980 m³/s (maximum flood and ebb discharges at the mouth have an order of magnitude of respectively m³/s and m³/s). The shape of the discharges are well represented by the model. In the Western Scheldt, the peak flood discharge tends to be underestimated and the peak ebb discharge tends to be better represented. Ebb and flood channel behave similar at Pas van Terneuzen, Zuidergat and Overloop van Valkenisse. The Gat van Ossenisse seems to transport relative to the Middelgat too much volume during flood. In the Lower Sea Scheldt (Oosterweel) the discharges are underestimated, while in the Upper Sea Scheldt (Schoonaarde) the discharges are overestimated. Final version WL2013R00_018_5rev2_0 36

45 Velocities at the stationary current measurement stations The currents have been analysed in the stations Wandelaar, Bol van Heist and A2B (MOW1) in the BCS and Oosterweel in the Lower Sea Scheldt (figure 8-17 and figure 8-18). Appendix E contains a more elaborated set of time series with modeled and measured velocities. In the BCS, the model reproduces smaller magnitudes for flood- and ebb currents with a RMSE value of 12 cm/s for station Wandelaar (bin 4), a RMSE of 25 cm/s for station Bol van Heist (bin 4) and RMSE values at A2B Boei of 22 cm/s and 15 cm/s at top and bottom. The maximum currents are underestimated about 30%. The directions are quite well prescribed at Wandelaar, Bol van Heist and A2B with an average deviation of respectively 11, 19 and 18. At Wandelaar, the MAE of the velocity components is about 12 cm/s and a corresponding RMAE about 27% which results in a good representation of the currents according to Sutherland et al. (2003) (Appendix A). At Bol van Heist the MAE of the velocity components is about 25 cm/s, with a RMAE around 45%. This corresponds to a reasonable/fair quality of the model. The MAE in A2B is about 0.20 cm/s with a RMAE of 39% what is just within limits of a good representation. The error increases from offshore towards the mouth of the Scheldt (Wandelaar, A2B, Bol van Heist). The stations Wandelaar and Bol van Heist are located near the Scheur, the shipping lane toward the mouth of the Scheldt. A2B boei is located closer to Zeebrugge. In the Lower Sea Scheldt a comparison is made with the current measurements at Oosterweel (top and bottom). The magnitude of the currents has a RMSE of 18 cm/s at the top and 14 cm/s at the bottom. The current is well represented during flood, but is underestimated during ebb. The deviation of the current is on average 11 at the top. On the bottom frequent erroneous measurements of the direction are present for the month of October and no analysis is made. The MAE of the components at the top is 18 cm/s, and the RMAE is 26% which results in a good quality of the model at this location. Salinity Figure 8-19 shows the computed and measured salinity at location Boei 84 (Sea Scheldt, in the vicinity of Deurganckdok). The model performs well, bearing in mind that salinity is modeled without separate calibration. The model has a slight systematic underestimation of one half parts per thousand (ppt), which is less than the accuracy of salinity measurements. The most offshore measurements are in station Vlakte van de Raan (Figure 8-19). The model represents the main variations in salinity, with a difference up to 1 à 2 ppt, although sometimes with a much slower response time. Appendix F contains time series of modeled and observed salinities. The results gives confidence in the model that the processes advection and diffusion that dominate the salt transport, are well represented. Final version WL2013R00_018_5rev2_0 37

46 Figure 8-13: Analysis of modelled (simg34) and measured tidal component M2 for amplitude (upper) and phase (lower). Final version WL2013R00_018_5rev2_0 38

47 Figure 8-14: Analysis of modelled (simg34) and measured properties of assymetry of vertical tide, amplitude ratio M4/M2 (upper) and phase shift 2M2-M4 (lower). Final version WL2013R00_018_5rev2_0 39

48 Figure 8-15: Vector difference (simg34 versus measurements) of the 10 main components (Z0, M2, N2, S2, L2, MU2, K1, O1, M4, M6) for the different stations along the Scheldt estuary. Figure 8-16: Low passed average error at Vlissingen of model results (simg34) minus measurements. Final version WL2013R00_018_5rev2_0 40

49 Figure 8-17: Modelled (simg34) and observed velocities in the BCS, Wandelaar (upper) and Bol van Heist (lower). Final version WL2013R00_018_5rev2_0 41

50 Figure 8-18: Modelled (simg34) and observed velocities in the BCS, A2B Boei (MOW1) (upper) and in the Lower Sea Scheldt, Oosterweel (lower). Final version WL2013R00_018_5rev2_0 42

51 Figure 8-19: Modelled (simg34) and observed salinities at the mouth of the Scheldt, Vlakte van de Raan (upper) and upstream in the Lower Sea Scheldt, Boei 84 (lower). Final version WL2013R00_018_5rev2_0 43

52 9. Conclusions and recommendations 9.1. Conclusions This report presents an actualization of the 3D NEVLA model with respect to the 3D NEVLA model (simg19) used in van Kessel et al. (2010). The following model changes were performed: Update of the model grid and bathymetry based on Maximova et al. (2009a and 2009b) to include all intertidal areas and the Durme until the tidal border and to improve the numerical schematization of the Deurganckdok. The training walls (strek- and leidam) are defined in the model bathymetry and the previous imposed thin dams are removed. The bathymetry in the BCS is improved by a better interpolation. A new set of initial conditions has been defined. The discharge at Merelbeke is optimized for smooth inflow through a new discharge location and new local bathymetry. The changes have led to a new reference run for the 3D NEVLA model, simg34, in which the hydrodynamics and salt transport for the year 2006 have been calculated. A comparison was made with the previous reference run simg19. The general behavior of the model remains the same, though local changes occur. The removal of the thin dams as a training wall and the bathymetrical change in the BCS cause only local changes in currents. The former also influences the higher harmonics upstream the Dutch-Belgian border. The bathymetry of Maximova et al. (2009b) has a smaller tidal storage volume and causes smaller ebb- and flood discharges in the Sea Scheldt. The model results of simg34 for 2006 show that the model is capable of reproducing the tidal hydrodynamics in the BCS and the Scheldt estuary. The model reproduces the combined effects on the main tidal components of convergence of the estuary and friction. A low pass filter of the model error is evaluated and indicates that a non-tidal error is already introduced at the boundary of the model. Analysis of current velocities indicates a good to reasonable quality of the model. Discharges through ebb and flood channels have similar shape in the model and measurements. The salinity in the model is reasonably well reproduced, which shows that the processes advection and diffusion that dominate the salt transport, are well represented Recommendations A number of further improvements could be investigated: Remove non-active cells. Based on a long term calculation (one year), the model results showed several cells never participated in the model. This became clear when velocity gradients occurred during flood discharges in the more upstream parts. Outer dike areas became initially wet due to high initial water level conditions in what was seen as good modelling practice. Due to the high initial water level were a stagnant water column of water is present at extended crests and outer dike areas. During flood events these reservoirs come in contact with the riverbeds causing high gradients in flow and non-convergence in the momentum equations. Research showed the model contains several non-active cells that never take part in the hydrodynamic cycle of flooding and drying but can lead to instabilities. Therefore it is recommended to remove these inactive cells where possible. Application of a more recent version of SIMONA. Both simg19 and simg34 are calculated in Simona More recent versions of the software have since become available. Weir Mechelen: In the 2D NEVLA model (WAQUA) it is possible to include a weir schematization. This is not possible in the 3D version (TRIWAQ) in the simona2007 version. The application of a new version of SIMONA would allow a better representation of the water levels in the Dijle. Final version WL2013R00_018_5rev2_0 44

53 Reducing error import at downstream boundaries. A non-tidal and tidal error are introduced at the boundaries of the model due to the modeling accuracy of the model train (ZUNO, CSM). A better representation of the hydrodynamics at the BCS in the ZUNO and CMS model will improve the NEVLA model performance. Alternatively the boundary conditions from the ZUNO model can separately be improved based on measurements near the model boundaries. Velocity field on intertidal areas. The quality of reproduction of velocities on intertidal areas is not known, but is important regarding to ecological aspects. A detailed analysis and calibration of the velocities in shallow and intertidal areas is recommended to improve future model applications. Final version WL2013R00_018_5rev2_0 45