DREDGING WORKS IN THE WESTERN SCHELDT TO DEEPEN THE NAVIGATION CHANNEL AND TO CREATE ECOLOGICALLY VALUABLE AREAS: STATUS AFTER 3 YEARS OF MONITORING

摘要

The Scheldt Estuary is an intensely shipped area, holding the fairway to the ports of Flushing, Terneuzen in the Netherlands and Ghent and Antwerp in Belgium. Since the 3rd deepening and widening of the fairway (2010), the shoals and sills along the main shipping channel are maintained at a depth of 14.5 m below LAT allowing for tide independent access to Antwerp for ocean ships up to 13.1 m draught.The sediment volume involved in the dredging activities amounts to 12.6 Mm~3 and 10.1 Mm~3 for the first two years and about 9 Mm~3 (preliminary) in the third year. The deepening volume (for the Western Scheldt) amounted to a volume of 7.7 Mm~3 as predicted in the environmental impact assessment. The maintenance volume is expected to further decrease due to the expected system's re-equilibration.The Flexible Disposal Strategy, aimed at creating ecologically valuable area, was set up in this framework. A first approach in the strategy is the disposal of dredged sediments on the edges of tidal fiats to create low-dynamic, shallow water areas, beneficial for fauna development. A second approach is to dispose sediments in the deep parts of the fairway and the secondary channels. This contrasts to the former disposal strategy that consisted of disposal solely into secondary channels.Monitoring data are continuously acquired (bathymetry, topography, ADCP, dredging and disposal data, ...) for assessment of morphodynamical and ecological consequences. If necessary, the disposal strategy is adapted to reach the desired ecological goals and mitigate possible undesired effects. This process of monitoring is captured in monthly data reports and yearly detailed analysis in which the so-called 'Quality parameters' are tested to well-defined criteria.In this paper we discuss the deepening and subsequent maintenance dredging works in the Western Scheldt for the first three years after the start of the project. We describe the process of monitoring and analysis as a decision-making instrument in the approach of the Flexible Disposal Strategy.