Optimization of the operational use of entrance channels based on channel depth requirements

Large capital and maintenance dredging operations are required to ensure the accessibility of many ports. The expenses associated with the dredging operations can have a significant impact on the finances of these ports. Therefore, considerable attention to the design of the width and depth aspects of access channels is justifiable. This study considered this topic within the framework of an Additional Master Thesis (3-month internship). The objectives of the study are: i) to verify the influence of different processes and sources of uncertainties in the evaluation of minimum depth requirements; and ii) to investigate the advantages and drawbacks of different methods of depth requirement evaluation. The Port of Tubarão (Southeast Brazil) is used as a case study to verify processes and methods. Four different approaches were considered to evaluate depth requirements for the access channel of the Port. These methods are based on either deterministic and/or probabilistic methods, and on approaches without or including wave influences. The results for the case study indicate that ship motions due to waves have a minor influence on the required channel depth at that location during most of the time. However, in certain wave conditions (not only in terms of wave height, but also wave period and wave direction relative to the manoeuvring ship) vertical ship motions become the dominant issue regarding depth requirements; consequently waves should be included in a practical evaluation over time. In probabilistic approaches more knowledge can be incorporated in the analysis, however, this requires detailed information. The deterministic approach, on the other hand, is simpler to use and gives good insight about the main driving variables. Although, the main drawback of deterministic methods is that the reliability of the evaluation cannot be accessed, or that conservative assumptions need to be made. This may be uneconomical. The use of a probabilistic method for the case study led to a more optimized use of the channel in terms of accessibility in comparison to the results obtained with the deterministic method. Nevertheless, those results depend largely on the safety factors assumed in the deterministic computations relative to the probability distributions considered in the deterministic approach. Alternatively, the safety margins can be computed or calibrated for specific cases based on probabilistic calculations. In that case the results of deterministic and probabilistic methods can be similar, ensuring the required reliability of the practical deterministic approach, but not being excessively restrictive.Ports and WaterwaysHydraulic EngineeringCivil Engineering and Geoscience