LTV O&M thema veiligheid: deelproject 1. Verbetering hydrodynamisch NEVLA model ten behoeve van scenario-analyse

In the framework of different projects, among which “LTV O&M thema Veiligheid - Deelproject 1” and “LTV O&M thema Toegankelijkheid - Ontwikkeling van een slibtransportmodel”, a calibration of the existing hydrodynamic NEVLA model of the Scheldt estuary is executed. This report gives a summary of all the steps which are undertaken to improve the model.The objective of the study “LTV O&M thema Veiligheid -- Deelproject 1” is to analyze the effect of different changes and their influence on the hydrodynamics of the estuary. Based on a literature review and data analysis some hypotheses concerning the change in tidal penetration in the estuary will be made. Afterwards these hypotheses will be verified with numerical models. In order to obtain reliable results, it is necessary that the numerical model performs well. Therefore a sensitivity analysis, a calibration and a validation of the NEVLA model, which will be used for 2D-3D hydrodynamic simulations, were carried out.The objective of the sensitivity analysis was to understand the impact of different model parameters on the tidal penetration. The results of this analysis are described in (Ides et al., 2008) and (Vanlede et al., 2008a). In (Vanlede et al., 2008b) the calibration was performed for the calculated water levels and discharges, based on the phase and magnitude of the most important harmonic tidal components of these parameters. In (Maximova et al., 2009) the calibration of the NEVLA model was extended. The resulting model parameters from (Vanlede et al., 2008b) were used as the reference simulation. The methodology was based on the comparison of phase and magnitude of the calculated and measured high and low water levels. This extended calibration was mainly focused on the Upper Sea Scheldt and the tributaries Zenne and Dijle because in these regions the differences between calculated and measured water levels were the largest. As a result of the calibration, the accuracy of the model for high water levels and low water levels was improved for most stations along the Scheldt estuary.The calibrated model was validated for a period with normal tide and for a period with an extreme high water. The calibrated model performs rather well for a period with normal tide. However, it does not simulate accurately a period with an extreme high water level. The reason for this and the possibilities to improve the model accuracy for such circumstances should be studied more in the future. The roughness field used for the calibrated model is strongly related to the bathymetry that was used during calibration of the model. If we use a different bathymetry for the scenario analysis the roughness field might change as well. Therefore, a simple roughness field without variation in the transversal direction was found, which gives rather similar results as the calibrated model with the space varying roughness field

Habitatmapping ondiep water Zeeschelde: deelrapport 2 - Numeriek 2D model

Shallow subtidal areas and intertidal zones are very important for the ecology of the estuary. These areas are characterized by low dynamics, which results in a silty and nutrient-rich environment. They form habitats for large bird polpulations and benthic species. The objective of the project “00_028 Habitatmapping ondiep water Zeeschelde” is to study the relations between the physical, sedimentological and ecological characteristics in the Sea Scheldt and to classify the shallow subtidal areas according to their ecological value (in collaboration with INBO). This report describes the calibration and validation of a numerical model. The model accuracy is analyzed based on comparison of the model results and measured water levels, discharges, stationary velocities and sailed ADCP measurements. The calibrated model will be used to analyse the hydrodynamic characteristics of the study areas

The unstructured Scaldis model: a new 3D high resolution model for hydrodynamics and sediment transport in the tidal Scheldt

In the framework of the projects "Integral Plan for the Upper Sea Scheldt" and "Agenda for the Future", the SCALDIS model, a new unstructured high resolution model of the tidal Scheldt is developed in TELEMAC 3D (Telemac-Mascaret software platform). Starting from the stated model purpose, a weighted dimensionless cost function is set up that attributes equal weight to the vertical and the horizontal tide. By adapting the bottom roughness, the cost function is minimized during model calibration. Quantification of the model skill and cost function calculation is done using the VIMM toolbox which is developed and maintained at Flanders Hydraulics Research. The quantified model skill of the SCALDIS model shows that the model is well suited to assess the effects of changing the bathymetry and geometry of the Scheldt river on water levels, velocities, tracer dispersion and residence times, and that the hydrodynamics can be used as the basis for sediment transport calculations (both cohesive and non-cohesive)

Vervolgstudie inventarisatie en historische analyse van slikken en schorren langs de Zeeschelde: scenario analyse 2D model

The research described in this report is made in the framework of the project Vervolgstudie inventarisatie en historische analyse slikken en schorren langs de Zeeschelde. The main purpose of the project is to investigate why some of the evolutions of the slikke and schorre area in the past – described in the report Van Braeckel et al. (2006) – did occur. The main tools to investigate these evolutions are measured data from the past as well as numerical models.With the numerical models different scenarios were studied in order to see how each of them influenced the tidal penetration in the Scheldt estuary. In fact it is change in tidal penetration that will affect the slikke and schorre area. In each scenario one possible cause of tidal change was implemented. A distinction was made between natural evolutions (sea level rise, changes in fresh water discharge) as well as human interventions in the estuary (poldering, straightening of the river, deepening of the navigation channel, …) in the scenarios. In Coen et al (2009) the results of the 1D model are described. In Ides et al. (2008) a sensitivity analysis of the 2D model is carried out, in order to have an idea about the uncertainty interval of the results of the different scenarios. In this report the results of the scenarios will be given

Integraal plan Boven-Zeeschelde: Subreport 1. SCALDIS: a 3D Hydrodynamic model for the Scheldt Estuary

In the framework of the projects 'Integrated plan for the Upper Sea Scheldt' and 'Agenda for the Future', it was necessary to develop a hydrodynamics and sediment transport model that covers the entire tidally influenced zone of the Scheldt Estuary and the mouth area, and that has sufficient resolution in the upstream part.Existing models lack a high resolution in the Upper Sea Scheldt, Durme, Rupel and Nete. For this reason, the SCALDIS model, a new unstructured high resolution model of the Scheldt Estuary is developed in TELEMAC 3D for the entire estuary, but with special attention to the upstream parts. The use of an unstructured grid allows to combine a large model extent with a high resolution upstream. The calibrated model will be used to analyse the effects of several scenarios (different morphology of the Scheldt with different ranges of boundary conditions).This report describes the model development, calibration and validation of the hydrodynamics. The model is calibrated for one spring-neap tidal cycle in 2013 against field data: water levels, velocities (in deep and shallow zones) and discharges

Numerical modelling of flood control areas with controlled reduced tide

The present paper focuses on the numerical modelling in TELEMAC-3D of flood control areas with controlled reduced tide structures along the Scheldt estuary and coastal zone for the storm event of December 6th, 2013. A new culvert functionality was implemented in the code to better represent the hydrodynamics of the exchange of water between the Scheldt estuary and these flood control areas with controlled reduced tide. Existing source and sink terms included in the code were paired and used as a culvert. The theoretical background to represent the different kind of flows through the culvert was based on the work of Bodhaine (1968). Additionally different head loss coefficients were introduced according to different geometric features of the culverts. The implementation of these new structures inside the 3D numerical model was validated using measured water levels in the estuary and inside the flooding areas , and using discharges (in and out) through the culverts measured only for one full tidal cycle. For the storm surge only measured water levels were available and these were compared with modelled ones

Werkgroep O&M - Projectgroep Veiligheid: Sub project 1. Data analysis and hypothesis - Lower Sea Scheldt

During the past centuries the tidal regime of the Scheldt estuary has seriously changed. This is due to different natural processes and human interventions in the estuary. An important question for the safety management in the Scheldt estuary is how the safety level changes on a long term, taking into account the historical and present human impacts (such as poldering, enlargement, etc.) and natural changes (sea level rise). An important aspect from viewpoint of safety management is the change of the high water levels during the coming decades. The changes in hydrodynamics and morphology of the estuary are related to each other.Within this report an analysis of both tidal and topo-bathymetric characteristics in the Lower Sea Scheldt since 1900 has been performed. The historical evolution of tidal parameters (high and low water levels, tidal range, duration of rising and falling, celerity of tidal wave) and topo-bathymetric parameters (hypsometric curves, channel volumes, volumes above intertidal areas) was investigated. For these tidal and topo-bathymetric characteristics several relationships were analysed. Long term evolutions show both similar as opposing trends for the investigated geographic sections (i.e. Parts of the estuary between water level stations) in the Lower Sea Scheldt