Assessing the accessibility of ports

Abstract

For seaports to be economically viable, they must be accessible for vessels. Due to the trend of increasing ship size and draught, the ports often must deal with high costs in maintenance dredging to ensure their maintained bed level (MBL). To reduce these costs, the definition of MBL has been subject to discussion in ports with muddy bed material. The Nautical Bottom Approach (NBA) was introduced for these ports. Instead of a static design MBL, the NBA defines the MBL as the level at which the density or yield stress of the bed material reaches a critical level (e.g., 1200 kg/m³ and 50 Pa). This creates the possibility to significantly reduce the dredging costs, while maintaining accessibility for incoming seagoing vessels.
To apply the NBA, new monitoring methods and dredging techniques are applied. Particularly, Rheotune and SILAS system were used to detect 1200 kg/m³ level before, during and after dredging with the Tiamat system. An optimal application of these methods requires proper knowledge of the bed properties and sediment behaviour in time and space. The density and yield stress measured by Rheotune should be properly calibrated before applying the measurement for the NBA.
In addition, there is a knowledge gap in the conversion from the measurements of the bed level properties to an actual applicable NBA. Several ports are using the density or yield stress critical limits to define their NBA. However, the critical limits often differ from port to port. Moreover, the effects of this approach towards the reduction of dredging efforts, while maintaining the accessibility of the port, are also unknown.
In this thesis the practical application of the NBA is being researched in combination with the effects it would have on the dredging strategy and the accessibility of the port. If a port has bed properties that imply the NBA could be used, it should also be researched what the effect will be on the port operations.
To find out what the effects of the NBA are on the accessibility of a port, the Port of Harwich has shared their data for this research. In the Port of Harwich several locations are present where mud will build up rapidly after (and even during) dredging works. With the data that has been shared by the Harwich Haven Authority, bed level models have been created, where the bed level is represented by several measurement techniques over the time. These bed level models are further used in a nautical traffic model to determine what the effects are on the accessibility of the port over time.
The results of this research show possibilities to implement the NBA within a port. By using variable bed levels, regularly surveying these bed levels and starting dredging works when necessary, a port can implement the NBA.
When a port authority has proper knowledge on its bed characteristics and changes their port operations to implement the NBA. The port can benefit by maintaining their accessibility for deep draughted ships, while lowering their dredging efforts.