Further development and first application of a mud transport model for the Scheldt estuary: in the framework of LTV. Phase 2

Abstract

In 2006, a work plan was conceived tor the development of a mud transport model tor the Scheldt estuary in the framework of LTV (Long Term Vision) (Winterwerp and De Kok. 2006). The purpose of this model is to support managers of the Scheldt estuary with the solution of a number of managerial issues. Also in 2006, the first two phascs were initiated. Thc present report discusses the actlvities that have been carried out during 2007, i.e. further improvement of the hydrodynarnic and mud transport model and lirst applicarion of the mud model to the release of fine sediment dredged from Sloe harbour, Vlissingen. At a technical level, all model improvements scheduled tor 2007 have been implemenred. The most important developments are: longer hydrodynarnic simulation period (3 month), more accurate concenration boundary condition, variable wave effects and biological effects. The hydrodynarnic sirnulation demonstrates realistic values for water levels, salinities and residual currents. Upstream of Antwerpen. the propagation of the tidal wave is modelled less accurately. Regarding the mud transport simulations, the following is concluded:
1. A minor shift of two dumping locations near Antwerp rnuch improves the proper modelling of the ETM.
2. New concentration BC at sea result in more realistic SPM concentrations and longshore SPM fluxes at sea.
3. The difference between simulations with 5 and 10 horizontal layers is only minor.
4 . Variable waves temporarily enhance the concenrations in the western part of the Western Scheldt during storrns.
5. The biological impact on large-scale SPM concentrations in the Scheldt estuary appears to be minor.
6. The SPM levels appear to be rather sensitive to the volume of harbour siltation and dumping.
7. The model cornputes an unrealistically high residual sediment flux towards the North Sea (about 2 MT/y).
If sediment dumping is in equilibrium with harbour siltation, this net export results in too low equilibrium SPM levels. Application of the model to the dumping of sediment dredged from Sloe harbour shows that a shift of the release location in western direction may be favourable because of a small reduction in local SPM levels and siltation rates.

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