River-induced flushing of the turbidity maximum in narrow estuaries.

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Johan Winterwerp, Miguel de Lucas Pardo, Bas van Maren, Julila Vroom, Zheng Bing Wang

Monday 29 june 2015

14:29 - 14:41h at South America (level 0)

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

Parallel session: 2J. Special session: Scheldt Estuary physics and integrated management

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In three previous papers (Winterwerp, 2011; Winterwerp and Wang, 2013; Winterwerp et al., 2013), we have argue that the Loire and Ems River have evolved into their current hyper-turbid state in response to large-scale engineering works, such as narrowing, rectification and deepening, sometimes accompanied by redirection of fresh water as well. In this paper, we show how fine sediments can build up in a flood-dominant narrow estuary at low river flows. Under normal flow conditions, the balance between river-induced flushing and estuarine circulation forms an estuarine turbidity maximum at the head of the salinity intrusion. At low river flows, this dynamic equilibrium is disturbed by the effects of up-estuary transport by tidal asymmetry and sediment-induced drag reduction. This conclusion follows from numerical simulations with Delft3D on the fine sediment dynamics in a schematized model of the Upper Sea Scheldt, the tidal river upstream of Antwerp.