Impact of dredging and dumping on the stability of ebb–flood channel systems

a r t i c l e i n f o The impact of dredging and dumping on the morphologic stability of the tidal channels is investigated using morphologic field observations for the Westerschelde estuary dating back to 1955. The results are used to verify the theoretical concept presented by Wang and Winterwerp (2001). This concept states that a critical threshold for the amount of sediment dumping exists above which a channel system in equilibrium may become unstable and degenerate. The value of this threshold amounts to 5–10% of the total sediment transport capacity. Verification of this concept using field observations is not straightforward as the morphology of tidal channel often changes as a result of both natural processes and human interferences, i.e. the channels are not in equilibrium. In addition, the morphological timescales associated with channel degeneration are large (decades to centuries). Verification of the theory thus requires a careful analysis of abundant morphological data and numerical modeling of sediment transports. The results of such analyses presented in this study confirm the existence and the approximate magnitude of the critical level for dumping that follows from theory. Refined guidelines are derived to use the theoretical concept as an engineering tool for the evaluation and design of strategies for dumping in estuarine multi-channel systems. In the absence of the required morphological data the indicative theoretical level of 5–10% can be used to obtain a first estimate of the dump capacity in two-channel systems. The Schelde is a tide-dominated estuary that is situated in the southwest of the Netherlands and Belgium. It includes the entire gradient from fresh to salt water areas providing various habitats for marine flora and fauna. In addition to these ecological values, the estuary is of large economic importance as it provides navigation routes to the ports of Antwerpen, Gent, Terneuzen and Vlissingen. The frequently conflicting economic and environmental interests make the management of the estuary a complex task. Collaboration of the Dutch and Belgium government has resulted in the formulation of a Long-Term Vision, hereafter referred to as LTV, for the Schelde estuary. Accordingly, a primary management objective for the estuary is a dynamic preservation of the physical characteristics and dynamics of the system of channels and shoals in the marine part of the estuary between Vlissingen and the border between The Netherlands and Belgium, referred to as the Westerschelde, Fig. 1. The morphology of the …