Port and channel sedimentation

Abstract

Maintenance dredging, as a result of port and channel sedimentation, can have a large share in overall maintenance costs of a port. A smart design can minimize the amount of maintenance dredging and thus improve the profitability of a port but also the long-term sustainability. As the preliminary design stages are often decisive for the final port layout, it is essential to quickly gain insight into the sedimentation quantities and governing processes, such that these can be accounted for in the port design. This leads to the main objectives for this research: - Develop a rapid integral modelling tool which accounts for the morphological aspects in and around a port, such as coastline evolution, sediment bypassing and port and channel sedimentation - Study the relation between port layout, coastline evolution and port and channel sedimentation The main process causing port sedimentation is the exchange of water between the port and the open sea. Water from outside the port brings in sediment which settles in the port basin. Three exchange mechanisms bring in sediment laden water: horizontal exchange due to eddy formation in the port entrance, vertical exchange due to density differences and tidal filling of the port basin. Channel sedimentation on the other hand is mainly caused by the reduction in velocity over the channel due to the increased depth. Not all sediment ends up in a port or channel. This part, the bypassing,moves beyond both breakwaters to either settle there or once again be part of the longshore transport. These processes can be represented by two empirical relations: SEDHAR (port sedimentation) & SEDPIT (channel sedimentation). These processes however need input in the form of (among others) flow velocities. A hydrodynamic model (Delft3D Flexible Mesh) is combined with these empirical relations to calculate this input for these relations. The hydrodynamic model is however not fast enough to take a longterm process such as coastline evolution into account. A hybrid model is developed by incorporating a 1D coastline model which is able to calculate long term coastline change as well as short term hydrodynamic processes. The hybrid model can be applied to calculate sedimentation for the port and channel in a matter of ‘minutes - hours’ for a period of many years. The change in (longshore transport) bypassing due to coastline evolution, is expected to relate to sedimentation. To verify the hybrid model it is applied to the port of IJmuiden in the Netherlands. The model results show its capability of predicting sedimentation for several decades relatively quickly (less than an hour). The model is however not capable of predicting increased sedimentationwhich is expected due to coastline change. Further analysis has on the other hand shown the impact of change in sediment concentration or change in port and channel geometry on sedimentation. The recommendation is to study sediment concentrations in and around the port more in detail and relate this to coastline change and sedimentation.