The vulnerability of tidal flats and multi-channel estuaries to dredging and disposal

Shipping fairways in estuaries are continuously dredged to maintain access for large vessels to major ports. However, several estuaries worldwide show adverse side effects to dredging activities, including a shift from multi-channel systems to single-channel systems and the loss of ecologically valuable intertidal flats. We used a time series of bathymetry of the Western Scheldt estuary (the Netherlands), morphodynamic model runs and physical scale-experiments to analyse the effects of dredging. All methods indicate that current dredging and disposal strategies are in the long run unfavourable because dredging increases the imbalance between shallow and deeper parts of the estuary, causing a loss of valuable connecting channels and fixation of the tidal flats and main channel positions. Changing the disposal strategy can be economically and ecologically better for the preservation of the multi-channel system. While future sea-level rise may revive the multi-channel system, further channel deepening will accelerate the adverse side effects.