Characterization of the impact of dredging and disposal on the channel network of the Western Scheldt estuary
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In recent history, the Western Scheldt estuary has been influenced by regular dredging and disposal operations performed to facilitate shipping. The exact response of the estuary to different dredging and disposal protocols is still not fully understood, while dredging and disposal is known to have an extensive range of effects that, in the case of the Western Scheldt, can threaten the multichannel system and ecosystem service functioning. The aim of this study is to assess the long term effects of three different dredging and disposal protocols on the tidal flow conditions and network complexity of the flow patterns in the Western Scheldt estuary. These effects and their morphologic impacts are examined and differentiated at a channel scale with the use of novel flow field based networks, and are compared to bathymetry based networks. After modelling the three dredging and disposal scenarios over 40-year periods, this study finds: a) a roughly 20% decrease in the number of active chute channels for all dredging and disposal strategies, with disposal in the main channel scours resulting in the highest mean number of active channels; b) a decrease in the area that is ebb asymmetric with disposal in the main channel scours and an increase with flexible disposal and disposal in the side channels and main channel scours. Until now, research has predominantly found a tendency towards ebb asymmetry with dredging and disposal which can increase erosion rates; and c) the strongest decrease in tidal flow conditions takes place in side channels and in the eastern part of the estuary, which can lead to increased sedimentation at those locations. Overall, disposal in the main channel scours seems to have a lower negative effect on the flow network complexity and tidal dominance in the estuary on the long term. The assessment is based on flow field networks, which on the whole, provide a good method to analyze tidal flow dynamics. The results in this study highlight the significance of the disposal strategy for future estuary management in the Western Scheldt and demonstrate that flow field based networks allow for efficient analysis of tidal flow dynamics at a channel scale.