This dissertation is triggered by the prevalent observation of conflicting stakeholder interests in highly urbanised deltas. These are coastal areas containing estuaries - i.e., water bodies where river water meets and mixes with seawater - which can form open or closed systems,
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This dissertation is triggered by the prevalent observation of conflicting stakeholder interests in highly urbanised deltas. These are coastal areas containing estuaries - i.e., water bodies where river water meets and mixes with seawater - which can form open or closed systems, and which can be natural or (highly) modified (e.g., trained, dredged or closed-off channels and canals). In these deltas, many stakeholders, including local communities, agriculture, shipping, and ecology, rely on estuarine services such as water safety, freshwater availability, deep and calm waters, and natural dynamics. Due to climate change and socioeconomic developments, many of these estuaries have become increasingly pressured, meaning that during extreme conditions, such as droughts, the variety of stakeholder interests can no longer be simultaneously satisfied. Consequently, system modifications to improve one stakeholder's interest may come at the expense of other stakeholders' interests, requiring complex trade-off decisions.
Here, waterborne transport is a key player. To facilitate the movement of goods and people, water transport entrepreneurs employ ever-larger vessels that call at ports ever more frequently. To accommodate this trend, waterways have been deepened and new lock complexes have been constructed. While such system modifications have brought beneficial effects to regional and (inter)national economies, they have also exacerbated saltwater intrusion, which negatively impacts freshwater availability during droughts. A framework to quantify a fair trade-off between the interests of waterborne transport and other estuarine user functions is currently absent. Instead, policy and decision-makers rely on qualitative analyses based on oversimplified models, hindering rational policy and decision-making. This problem particularly holds for the impact of physical system changes on waterborne transport performance, which are often not quantified.
Consequently, interventions aimed at improving waterborne transport often neglect the potential negative impacts on other stakeholders, leading to suboptimal and non-integrated solutions that may be ineffective in the long run.
The objective of this dissertation is, therefore, to assemble a methodological framework that can rationally quantify the trade-offs between impacted stakeholder interests for interventions in systems where waterborne transport plays a significant role. To achieve this, a two-step approach is followed. First, a method is developed to quantify the impact of system modifications in estuaries on waterborne transport performance. Second, this quantification method is included in a framework that can evaluate multi-stakeholder interests for an intervention in the estuary. This framework results in a trade-off curve between the impacts on the stakeholders' key performance indicators.
As a result of the first step, this dissertation found that vessel waiting times are the key performance indicator for quantifying the impact of system modifications on water transport. These waiting times are primarily caused by the cascading effects of downtime and congestion, which are currently not quantified by any existing method. To include these effects, this dissertation identified the open-source simulation library OpenTNSim to be the most suitable for further development. Additional modules were developed and added to this library to resolve the aforementioned `cascading effects of downtime and congestion' for both open and closed estuarine systems. The proposed quantification method was validated by its implementation as a nautical traffic model in a real-world case study of seagoing vessels calling at a liquid bulk terminal in the Port of Rotterdam. In this case, the nautical traffic model was considered valid when a sufficient part of observed waiting times could be reproduced and explained. One year of AIS data was analysed to obtain a representative fleet in the model with realistic origins, destinations, speeds, turning times, and laytimes at the terminal and anchorage areas. In addition, geospatial data and one year of hydrodynamic data were used to derive model input. Together with the actual maintained bed levels, port layouts, and tidal accessibility policies, the model resolves tidal downtime and infrastructure congestion. Analysis of the model results reveals that the nautical traffic model was able to unravel 73.4\% of the observed non-excessive vessel waiting times. Moreover, the unresolved excessive waiting times are believed to be caused by other processes that are not related to the system's state. Hence, the implemented method is considered valid to quantify waterborne transport performance as a function of the physical system.
In the second step, the now-validated quantification method for waterborne transport performance was included in a developed framework to evaluate trade-offs between the stakeholders' interests. The framework entails a train of models that link state indicators of the physical system to performance metrics for stakeholder interests. The model results are used to quantify the trade-off between port performance and freshwater availability as a function of bed-level variations in the open system of the Nieuwe Waterweg (NWW) in the Rhine-Meuse Delta. The resulting impact curves are insightful; they reveal how waterborne transport performance and freshwater availability compete as the bed level of the NWW changes. Freshwater availability improves when the bed level is raised, albeit at the expense of water transport performance, while water transport performance improves when the NWW bed level is lowered, albeit at the expense of freshwater availability elsewhere in the estuary. By adding valuation functions to each of the performance curves, stakeholders can express how important they find certain levels of performance loss. Ultimately, the framework leads to an optimal depth, although this decision remains a political process.
In conclusion, this dissertation enables a more rational trade-off between stakeholder interests in estuaries where water transport plays an important role. The underlying agent-based nautical traffic modelling method, implemented in the OpenTNSim library, and trade-off framework can be further expanded and applied. For this, further validation of the modules is recommended, particularly for closed systems, as they were only validated for open estuaries, with a specific focus on tidal windows and salt intrusion effects. Furthermore, to extend the applicability of the proposed quantification method for water transport performance, this dissertation recommends considering the incorporation of additional physical factors that affect downtime and additional sources that contribute to congestion. This may require the incorporation of additional datasets and the involvement of additional computing power. Moreover, to extend the applicability of the trade-off framework, it is advised to incorporate additional stakeholder interests and to involve stakeholders in constructing realistic valuation functions. With these additions, the proposed approach becomes more widely applicable, opening the door to its application to other estuaries around the world. @en
