Effects of dredging and dumping in laboratory scale experiments of estuaries

Abstract

Shipping fairways are continuously dredged to maintain and increase access of large ships to major ports located in estuaries, for example the port of Antwerp in the Western Scheldt. However, it has been shown in various estuaries worldwide that there are several adverse side effects of these actions including loss of ecologically valuable intertidal area, increased tidal range and increased wave propagation speeds which results in flooding. The Western Scheldt estuary is one such estuary which has undergone both channel deepening events (capital dredging) and maintenance dredging, which takes place on a continuous basis to maintain a minimum depth required for shipping. This thesis examines the effects of dredging and dumping on the morphology of estuaries at a variety of spatial and temporal scales. This was done using a scale experiment in combination with detailed analysis of the Western Scheldt estuary. A scale experiment was designed with a dredging and dumping protocol based on past and current practices in the Western Scheldt. Information about these practices came from reports, papers and supporting literature, combined with detailed analysis of digital elevation models of the estuary (DEMs) from 1955-2015. A shipping fairway was dug with dimensions scaled on measures taken in the Western Scheldt and consequently maintained to a minimum depth requirement with removed material being dumped back in the system. Dumping locations were based on current practices in the Western Scheldt. Results from the experiment are compared with a control experiment without dredging or dumping. The implications of dredging and dumping were seen on both an estuary wide scale and individual morphological features over a variety of temporal scales. The experiment replicated the processes occurring in the Western Scheldt and other estuaries worldwide including adverse effects such as decreased intertidal area, increased high waters, increased tidal range, increased tidal penetration and a tendency for the main channel to silt up more quickly. It also indicates which dumping locations result in sedimentation/erosion and the importance of distance along the estuary in determining this. To maintain the sediment budget of sandy multi-channel systems such as the Western Scheldt and to combat negative and potentially dangerous effects (particularly with the threat of sea level rise) of dredging and dumping further human interference will be needed.