A smooth Scheldt

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Jelmer Cleveringa, Marcel Taal

Monday 29 june 2015

12:00 - 12:15h at South America (level 0)

Themes: (T) Special session, (ST) Scheldt Estuary physics and integrated management

Parallel session: 1J. Special session: Scheldt Estuary physics and integrated management

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The Scheldt estuary delivers important (ecosystem) services, as a shipping lane, a nature reserve and in the protection against flooding. Ongoing studies of various aspects of estuarine development are an essential element of the estuarine management and this study is one example from many, executed in cooperation between the Netherlands and Flanders. The bathymetry of the Western Scheldt, the Dutch part of the Scheldt estuary, is measured each year. The abundance of data allows for detailed analysis of the morphology at scales that range from the (sediment volume of the) entire basin to the evolution of individual tidal flats and small tidal channels. Additionally the interpretation of aerial photographs of the intertidal and supra-tidal environments provides detailed information on the abundance of bed forms (mega ripples). A decline in the number of small tidal channels – ebb- and flood chutes and channels that connect the main ebb- and flood channels, is observed throughout the Western Scheldt. The large number of small tidal flats have merged into a limited number of bigger entities, and the jagged edges of the flats have given way to almost straight water lines. The surface area of the inter-tidal flats that is covered with mega-ripple fields has decreased. The overall change is from an irregular distribution of inter-tidal flats with branching channels and shallow areas towards smooth tidal flats in between the main channels. Causes for the smoothing of the Scheldt have not yet been found. Hypotheses and explanation have to account for the distribution of the change throughout the Western Scheldt. Explanation on the scale comprise intrinsic pattern development and/or the closure of branching tidal basins. Changes in the propagation of the tidal wave are ruled out as an explanation, because these are more pronounced in the eastern reaches. Future research, including numerical modelling simulations may provide more insight in the underlying mechanisms. Estuarine management needs to incorporate the fact that the future Scheldt will be a smoother Scheldt. The present and future morphology of the tidal flats and small channels differs from past patterns. Values that are associated with this morphology have and will changed and it may require tailor-made measures to retain them.