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Op 10/04/2017 werd het Waterbouwkundig Laboratorium per mail gevraagd naar de mogelijkheid om een snelle en indicatieve berekening uit te voeren naar de vereiste bodemprofielen om te voldoen aan onderstaande klantenwensen: Tankvaart Kieldrechtsluis bij diepgang 16.5 m en minimale tijpoortlengte gelijk aan 2 uur: - Opvaart (scenario 1a en 1b) - Afvaart (scenario 2) Containervaart Deurganckdok bij diepgang 18.0 m en minimale tijpoortlengte gelijk aan 1 uur: - Opvaart (scenario 3) - Afvaart (scenario 4) Bulkvaart Vlissingen Sloehaven bij diepgang 17.0 m en een minimale tijpoortlengte gelijk aan 30 minuten - Opvaart met stroomcriterium [-15 minuten SvH;+15 minuten SvH] in 90% van de tijen (scenario 5). In het kader van voorliggende opdracht ontwikkelde WL een rekenmethodiek die toeliet om uitgaande van een vooropgestelde toegankelijkheid een minimaal vereist diepteprofiel te berekenen. Hierbij wordt iteratief een gelijkwaardige verdieping toegepast op de openings- en sluitingsdrempels van een tijpoortberekening. Per drempel kon bovendien een maximale diepte gedefinieerd worden waaronder de drempel niet verdiept mocht worden. De rekenmethodiek werd toegepast op bovenvermelde klantenwensen en resulteerde voor elk in een geoptimaliseerd diepteprofiel. Op basis van de resultaten is een inschatting mogelijk van de vereiste inspanningen om te voldoen aan de klantenwensen.

Scheldt River (Netherlands and Belgium: Mouth)

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The specific objective of this study is to investigate impact of the presence of secondary tidal basins on long-term estuarine morphodynamics. To this end, first, a morphodynamic model using Delft3D software is set up, which is able to reproduce large-scale bottom features similar to those observed in real estuaries. Second, runs are conducted with the latter model in case that secondary tidal basins are present. The Scheldt estuary is selected as the study area, where multiple secondary tidal basins were present in the past (e.g. Sloe and Braakman). To compare model results with observa- tions, secondary tidal basins are constructed at the same positions as those of former basins Sloe and Braakman. In the case of using present geometric shape of the Scheldt estuary (default case), good resemblance between modeled and measured bathymetry is observed, even though significant differences occur. In particular, the simulated formation of a shallow region in the mouth of the estuary flanked by two distinct southern and northern channels, and of a system of straight and meandering channels inside the estuary, are large-scale features that are comparable to observed bathymetry. Moreover, the simulated connection between the main ebb channel in the estuary and the southern channel in the mouth, with the latter extending seaward over time, is confirmed by historical bathymetric data. A significant difference between simulated and measured bathymetries is that the southern channel in the mouth area forms too far south compared with the observed main channel in this area (Wielingen). Another major difference is that many small-scale secondary channels appear in the mouth, which are not observed in the field. Appearance of these small-scale bathymetric features is attributed to neglecting of waves. Similar to the case of absence of secondary basins (default case), a system of straight flood and meandering ebb channels occurs also in case of presence of the Sloe basin. Main difference is that in the latter case, the part of the ebb channel that is located near this basin forms 2 km more to the south with respect to its location in the default case. These results suggest that the presence of this secondary basin causes a locally southward migration of the ebb channel. Similar southward migration of the ebb channel occurs in case that both Sloe and Braakman basins are present. However, in this case, the meandering ebb channel is wider and the flood channels are less pronounced compared with those in the case of only the Sloe basin. Adding only the Braakman basin weakens the connection between the landward and seaward parts of the ebb channel, which results in a decrease of the sinuosity (meander) of this channel. The presence of Braakman basin does not result in a local displacement of the ebb channel, which reveals the importance of basin location. Results further show that the presence of secondary tidal basins leads to changes in the shape of the meandering ebb channel, such that the connection between the latter channel and the southern channel in the mouth area is weakened, particularly in the case of Braakman basin. This means that the presence of a secondary tidal basin inside the estuary not only have local morphodynamic effects, but it can also have significant impact on the morhodynamic evolution of the mouth of the estuary. This is also confirmed by the fact that sand balance of the entire estuarine system (estuary+mouth) changes significantly in case that secondary basins are added to the system. Based on the model results, it can be stated that observed northward migration of the ebb channel near the location of former secondary basin Sloe is due to closure of this basin. Moreover, these results suggest that the closure of Sloe and Braakman basins probably have affected to morphological evolution of the Scheldt mouth area.

Scheldt River (Netherlands and Belgium: Mouth)

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Scheldt River (Netherlands and Belgium: Mouth)

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This report is an extension to the work previously reported by Chu et al. (2019). During the discussion of the results, the suggestion was given to lower the weight of the stations in the Rupel Basin in the cost function that is used in the automatic calibration procedure, and check the influence on the end result. This report follows up on that suggestion. The weights in the cost function for the water level stations in the Rupel basin are made 16 times smaller. The model is then automatically calibrated on bottom roughness for the entire year of 2007. The result of lowering the weight of the stations in the Rupel basin in the cost function is that (as expected), the error on water levels in the Rupel basin slightly rises by 1-2 cm. The model however performs slightly better from Hemiksem to Walem (also by 1-2 cm). The re-calibrated model shows an unchanged (good) skill representing the salinity and cross-sectional discharge in the Scheldt estuary. As expected, the model performance in the Western Scheldt is unaffected by the change in weights.

Scheldt River (Netherlands and Belgium: Mouth)

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Scheldt River (Netherlands and Belgium: Mouth)