Assessing maintained bed levels in ports

Abstract

The accessibility of a port, which is mainly determined by the available water depth, is of economic importance for a port to distinguish itself from other ports. For the vertical design of navigation channels, the goal is to make routes equally accessible and not have bottlenecks; to have an optimal maintenance program and not incur unnecessary costs. Ultimately, the vertical design of channels entails a trade-off between the Maintained Bed Level (MBL), vessel draughts and the percentage of accessibility. The objective of this research is to assess available and required water depths in ports, and to identify opportunities for the vertical design of channels. To reach this objective, a literature study has been carried out. Vertical design approaches, vessel characteristics, local conditions and admission policies are considered. Also, since this topic is strongly related to practice, a relatively large number of interviews were conducted. In this study, a new, more detailed vertical design approach has been framed. The vertical design of channels revolves around available and required water depths. Since parameters to determine these depths vary in time and space, a systemic-view is required to design for the same accessibility percentage along a route. In this research, a general method to quantify accessibility percentages as a function of the MBL in a port-network has been framed. By looping over the MBL, corresponding accessibility percentages can be calculated. As a result, it becomes possible to maintain bed levels for neither too little (bottlenecks) nor too much (unnecessary dredging costs) available water depth. Also, assessing the actual draught of vessels for vertical channel design purposes appears relatively new. A Port of Rotterdam case study is performed to analyse the traffic data and to validate the results of the computer model. Four terminals, with different business-dynamics, handling the largest-draughted vessels, were selected. The results of this study are presented and supported by relevant actors in the port: shipping line, terminal, port authority and pilot. From the traffic study, it was concluded that there can be a significant discrepancy between actual and design vessel draughts. For example, only <0.1% of the largest container vessels (16-17m vessel design draught) handled in the Prinses Amaliahaven (almost) reach the draught for which channels has been designed (17m). Moreover, the MBL model allows a port authority to be more rational about where to maintain for which bed level. By removing structural over-depths, dredging costs can be saved. By removing bottlenecks, entire routes can become more accessible with relatively little dredging work. It would be recommended to review the actual use and accessibility of channels in ports on a regular basis (with the MBL model). The MBL model has a general set up; it can be applied to ports all over the world. Overall, it would be expected that something as fundamental as the MBL would be fully thought out in ports. It is compelling that by combining different data-sets (water levels, actual vessel draughts, and currents in case of a tidal window), room for improvement can be found.