A new disposal strategy in the Schelde-estuary: using dredged sediment to create benefits for nature

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Yves Plancke, Gwendy Vos, Marco Schrijver

Chair(s): Mark van Koningsveld

Monday 29 june 2015

17:00 - 17:15h at Antarctica (level 0)

Themes: (T) Special session, (ST) Building with nature

Parallel session: 3D. Special session: Building with Nature

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To guarantee optimal port accessibility, the deepening of the navigation channel was executed within the scope of the LongTermVision for the Schelde estuary. As the estuary is part of the Natura 2000 network, both an EIA and AA were necessary. A new disposal strategy was proposed, using dredged sediments to create opportunities for nature development. This new strategy was first investigated by Flanders Hydraulics Research, combining several research tools, and performing 2 in situ disposal tests. After a positive evaluation of the tests, the strategy was further developed, and 4 locations were chosen to apply the strategy to. The main idea of the strategy is using dredged sediments to create morphological structures that influence the flow patterns, creating low dynamic areas, which are suited for ecological purposes ("working FOR nature"). Since the 4 locations each have specific characteristics, site-specific relocation strategies were developed, taking into account local flow and sediment characteristics. For 2 locations at the tip of a sandbar a "megadune" has been realised, creating a shadow zone behind the megadune. For the other 2 locations located along a sandbar, a "sandspit" has been realised, aiming at guiding the flow away from the sandbar. To evaluate the success of this new disposal strategy, an extensive monitoring program was set up and several criteria were defined. Before the start of the deepening the reference situation was monitored. Since then, new measuring campaigns at all locations have been executed to evaluate the effect of the works. Recent results show different effects near different sandbars, both for sediment stability as changes in flow velocities. Nevertheless, ecological results are promising: the first results show an increase of almost 100 ha new low dynamic habitat. During the following years the new strategy and the monitoring will continue, allowing the evaluation of the new disposal strategy on the longer term.