Presence of connecting channels in the Western Scheldt Estuary

To predict the effects of dredging operations in the Western Scheldt estuary, insight into the morphological behaviour of its channels is needed. The estuary features two large main channels that meander alongside each other and that are linked by smaller connecting channels. These connecting channels originate from water level differences between the two main channels. Three hydrodynamic mechanisms are investigated that are responsible for generating such water level differences: (1) differences in tidal wave propagation along two neighbouring main channels, (2) centrifugal forces, and (3) Coriolis forces.The magnitude of the three mechanisms is analytically assessed based on channel geometry, which is derived from historical depth charts. The analysis demonstrates a large temporal variability of the water level differences due to tidal wave propagation, mainly as a function of changes in the depth ratio between the two main channels. Conversely, both the centrifugal effect and the Coriolis effect are relatively constant over time. The temporal evolution of the connecting channels can therefore primarily be attributed to the wave propagation mechanism. A correlation analysis reveals a linear relationship between connecting channel dimensions and the net water level differences produced by the three processes.The relationship suggests that dredging operations may significantly influence the evolution of connecting channels by changing the depth ratio between the two main channels. The proposed future deepening of the navigation channel is therefore expected to induce a decline in the size, or even a total disappearance, of connecting channels in some parts of the estuary

Tidal flow separation at protruding beach nourishments

In recent years, the application of large-scale beach nourishments has been discussed, with the Sand Motor in the Netherlands as the first real-world example. Such protruding beach nourishments have an impact on tidal currents, potentially leading to tidal flow separation and the generation of tidal eddies oflength scales larger than the nourishment itself. The present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions, based on extensive field observations and numerical flow simulations. Observations of the flow field around the Sand Motor, obtained with a ship-mounted current profiler and a set of fixed current profilers, show that a tidal eddy develops along the northern edge of the mega-nourishment every flood period. The eddy is generated around peak tidal flow and gradually gains size and strength, growing muchlarger than the cross-shore dimension of the coastline perturbation. Based on a 3 week measurement period, it is shown that the intensity of the eddy modulates with the spring-neap tidal cycle. Depth-averaged tidal currents around coastline perturbations are simulated and compared to the field observations. The occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape. Results show that several different types of behavior exist, characterized by different combinations of the nourishment aspect ratio, the size of the nourishment relative to the tidal excursion length, and the influence of bed friction.Coastal EngineeringEnvironmental Fluid Mechanic

Understanding coastal erosion processes at the Korean east coast

Rivers, Ports, Waterways and Dredging EngineeringCoastal Engineerin