Author(s): B. Hofland; H. Christiansen; R. A. Crowder; R. Kirby
Linked Author(s):
Keywords: Current deflecting wall; Siltation; Density current; Harbour design
Abstract: Sedimentation is a serious problem for harbours around the globe. Sediment is transported into a harbour by various exchange mechanisms. A relatively new means to reduce harbour sedimentation of river harbours in tidal conditions in a passive manner is the Current Deflecting Wall (CDW). The main effect of a CDW in a harbour without density differences is that all the water that is needed for tidal filling is "caught" from the upper parts in the water column. This water contains little sediment. In order to determine whether a cdw can also work when density-induced exchange currents are present, laboratory experiments were executed. Several CDW configurations were optimised and compared visually. The configuration that seemed to decrease the exchange most was tested in detail. Especially the flood period was studied closely. During flood most river water enters the harbour basin due to tidal filling and the density current. During a large part of the flood period flow velocities in the flume are high enough for the CDW to function. With the CDW in place, the water that flows into the harbour during rising tide originates from the upper water layer in the flume. Hereby the influx of near bed water is substantially decreased. It also increases the density difference however, which causes a small extra exchange around high water slack. This effect is only minor when compared to the decrease of exchange of near bed water. It can be concluded that the CDW tested is able to decrease the influx of sediment due to density currents, but for quantification site-specific hydraulic modelling is required.
Year: 2001