Trading off dissimilar stakeholder interests: Changing the bed level of the main shipping channel of the Rhine-Meuse Delta while considering freshwater availability

Climate change and socioeconomic developments have led to highly stressed estuarine systems in which dissimilar and conflicting stakeholder interests can no longer be satisfied simultaneously, inevitably resulting in trade-offs. Since translating these stakeholder interests into quantifiable performance indicators is challenging, policy and decision-makers are often bound to qualitative trade-off assessments, potentially resulting in suboptimal system interventions. In this paper, we assess the well-known socioeconomic trade-off in estuaries worldwide: port accessibility versus freshwater availability. We consider the severely dry year of 2022 in the Rhine-Meuse Delta, for which we assess the effects of bed level change. To quantify the trade-off, we apply a general framework of performance indicators determined based on models that use the output of a validated hydrodynamic model, including salt transport. Port accessibility was quantified based on vessel waiting times, using a data-driven nautical traffic model. For the performance indicator of freshwater availability, we developed a metric that includes storage capacity. The method resulted in a trade-off curve showing improved freshwater availability and deteriorated port accessibility for decreasing bed level. This trade-off curve provides valuable insights into system interventions in a multidisciplinary setting, being an intuitive visualisation showcasing the (non-monetary) benefits and costs for different stakeholders with dissimilar interests. As the method could be expanded and applied further, this study aids quantitative policy and decision-making.