|Data-analysis water levels, bathymetry Western Scheldt|
Kuijper, K. (2013). Data-analysis water levels, bathymetry Western Scheldt. International Marine & Dredging Consultants/Deltares/Svašek Hydraulics BV/ARCADIS Nederland BV: Antwerp. 125 + annexes pp.
tide, bathymetry, high water, safety, natural changes, human impact, Westerschelde, analytical model
Water level data and bathymetric data of the Western Scheldt have been analysed to study the evolution of high and low waters and their propagation velocity since the end of the 19th century. Analysis of the measured tidal propagation shows that since the end of the 19th century the tide in the Western Scheldt has become more dynamic. This follows from the increase of the tidal range and the larger propagation velocity. In addition the mean water level has risen which is largely due to mean sea level rise. The overall effect is that the high waters and to a lesser extent the low waters have increased in the estuary. The increase of extreme high waters seems to be somewhat larger than that of yearly-average high waters.Differences between ebb- and flood dominance have become smaller converging to almost neutral conditions along the Western Scheldt. With respect to tidal volumes the largest changes have occurred for the individual main and secondary channels east of Terneuzen with the former increasing at the expense of the latter. The tidal volume as sum of both main and secondary channel indicates an increase in the eastern part of the Western Scheldt but less clear trends in the other regions.Bathymetric changes since 1955 indicate that the channel volume has increased which has resulted in larger channel depths. At the same time the water volume above the intertidal flat area has decreased. Thus tidal flow has increased at the expense of tidal storage. The sand volume of the intertidal flats has become considerably larger while the intertidal area has increased only slightly. As such the intertidal flats have become higher. The overall picture is that since 1955 sand has been redistributed resulting in deeper channels and higher intertidal flats. For the individual sections Vlissingen-Terneuzen, Terneuzen-Hansweert and Hansweert-Bath the overall characterization of hydrodynamic and bathymetric changes may be somewhat different.Effects of human interventions such as land reclamations, channel deepening, normalisation works (‘leidammen’) and the Deltaworks could not be retrieved from data records on high and low waters, tidal range and amplification.The application of an analytical model on tidal propagation showed that the major features as tidal range, amplification and propagation velocity were well represented by the model. The enhanced amplification of tidal range for the section Hansweert-Bath could be explained by the model indicating that changes in overall channel depth played a major role.Furthermore it is predicted that for channel depths larger than 15-20 m the tidal range will reduce. This effect may be (partly) compensated by an increased tidal range of the tidal wave coming from outside the estuary (North Sea) as observed during the past 100 years.