The current deflecting wall in a tidal harbour with density influences

Abstract

Siltation is a serious problem for harbours situated on tidal rivers and estuaries. Maintenance dredging is necessary on a regular basis to guarantee safe navigation and is often a large cost factor. A means to prevent sediment from entering a harbour is the Current Deflecting Wall (CDW), which passively alters the water exchange at the harbour entrance. The established beneficiary effects ofthe CDW during rising tide under tidal conditions with homogeneous density are: 1) The mixing exchange between harbour and river is reduced. 2) The water needed for tidal filling is captured by the CDW from the top layer of river water, which contains less sediment. 3) An over-capture of water by the CDW pushes the mixing layer away from the harbour basin. This final thesis presents the findings ofthe experiments on the effect of a Current Deflecting Wall on siltation reduction in harbours. The experiments were executed in the tidal flume at Delft Hydraulics. The experiments were conducted in the framework ofthe European Community's LIP III program. Aim of the study The thesis work had the following objectives: 1) Quantification ofthe effect of a CDW on water exchange between harbour and river under quasi-tidal flow and homogeneous conditions (constant water density, constant discharges through the flume and the harbour). These tests were performed during Phase 1. 2) Investigation ofthe influence of a CDW on water exchange between harbour and river under tidal flow and inhomogeneous conditions (salinity gradients). These tests were performed during Phase 2. 3) Development of the experimental measurement techniques Dye Concentration Measurements (DCM) and Particle Tracking Velocimetry (PTV) for quantification of water exchange between harbour and river. The emphasis ofthe current study was on the second objective because the CDW had not been studied under inhomogeneous conditions before.