Maintenance dredging in ports and waterways is essential to ensure safe navigation. With increasing regulatory pressure on the maritime sector to reduce exhaust emissions, both dredging contractors and port authorities are seeking effective mitigation strategies. However, accurate emission estimates for maintenance dredging activities are still limited in the literature and often rely on experiential knowledge rather than scientific methodologies. This study suggests a method for estimating emissions and comparing alternative maintenance dredging strategies by quantifying trade-offs between project duration, energy consumption, and emissions. The method integrates vessel characteristics, project specifications, and sediment properties to allow for situation-specific, realistic assessments. A discrete-event simulation is used to evaluate two alternative scenarios, offering insights into the impact of key parameters on vessel selection and overall operational efficiency. The method is demonstrated using a case study of the Port of Ramsgate (UK), where estimated results are compared with real-world data for validation. Finally, the study outlines theoretical and managerial implications and suggests directions for future research.

Inland waterway transport (IWT) is one of Europe’s most energy-efficient freight modes, requiring far less energy per tonne-kilometre than road or rail. Yet, it still contributes to greenhouse gas emissions. Under the European Union (EU) commitment to climate neutrality by 2050, transitioning IWT to zero- emission (ZE) operation has become a key but complex systemic challenge. IWT system performance is shaped by fluctuating water levels, which affect navigability, vessel loading capacity, and energy consumption, as well as by infrastructure constraints and an ageing, heterogeneous fleet. Addressing these challenges requires an integrated approach linking multiple systems, domains, and spatial and temporal scales. A digital twin can provide such a framework by integrating logistics, infrastructure constraints, environmental conditions, fleet composition, operational dynamics, and energy systems. This enables stakeholders to assess operational, tactical, and strategic decisions within a consistent digital environment.

Addressing these challenges requires an integrated approach linking multiple systems, domains, and spatial and temporal scales. A digital twin can provide such a framework by integrating logistics, infrastructure constraints, environmental conditions, fleet composition, operational dynamics, and energy systems. This enables stakeholders to assess operational, tactical, and strategic decisions within a consistent digital environment.

Mud is a fine-grained cohesive material which contains mineral particles (predominantly clay and silt), organic (and inorganic) matter, and water. Understanding mud’s rheological and settling behaviour is critical for sustainable sediment management in ports [1, 2]. A systematic analysis of the effect of clay minerology on the rheological and settling behaviour of mud has been conducted previously [3, 4]. In contrast, literature on the impact of organic matter on physical properties of sediment is scarce. Our previous work [5] demonstrated the impact of microbial inactivation via gamma radiation, revealing a significant increase in settling rates. Current research incorporates chemical sterilization (NaN3) and organic matter removal (NaOCl), to systematically differentiate between effects of microbial activity and effects of organic matter on the physical properties of fluid mud (FM).

Floc size distribution and settling velocities are crucial parameters for characterising cohesive sediments, as they influence how these sediments behave in various environmental settings. The accurate measurement of these properties is essential, with different methods available depending on the scope of the study. For long-term monitoring, in situ techniques based on laser diffraction are commonly used, while video microscopy techniques are preferred for shorter studies due to their ability to provide detailed information on individual particles. This study compares two high-magnification digital video camera setups, LabSFLOC-2 and FLOCCAM, to investigate the impact of particle concentration on settling velocity in flocculated sediments. Flocculated clay was introduced into settling columns, where both the size and settling velocities of the flocs were measured. The results obtained from both setups are in line with each other, even though the FLOCCAM was slightly more efficient at capturing images of small particles (of size less than 50 microns) and LabsFLOC-2 was better at detecting large size fraction particles (having a low contrast due to the presence of organic matter). Floc size and settling velocity measurements from both setups however exhibit mostly similar trends as a function of clay concentration and the same order of magnitudes for the recorded settling velocities.

Dewatering of dredged sediment often relies on chemicals and heavy machinery, which increase fossil fuel use and emissions [1]. Traditional sediment dewatering methods only worsen the financial and environmental burdens associated with sediment management. When the slurry eventually dries at dewatering fields, it is perceived that the biological quality of the resulting sediment does not meet the standards of healthy soil, meaning it is rarely reused. It is also important to note that none of the existing commercial dewatering methods improve the environmental quality of the final product; they only address its physical properties.

Over the past decade, more nature friendly innovative methods have been developed [2]. These methods use only endemic fauna and flora to significantly accelerate the dewatering process for various types of slurry. Additionally, the treated final product resembles closely biological properties of soil. Soil is a valuable resource, which would otherwise need to source it from the commercial soil market, a process that is both expensive and environmentally harmful due to operations-related emissions.

The UK’s largest container port at Felixstowe, faces significant sedimentation challenges, with approximately 2.4 million m³ of sediment requiring management annually [1]. To optimize maintenance strategies and enhance navigability, Harwich Haven Authority is exploring the implementation of PIANC’s nautical bottom concept [2], which relies on understanding the rheological and settling behaviour of muddy bed in the port.

This study examines the shear strength (yield stress) evolution of soft mud layers by investigating their physical properties (e.g., density, organic matter, salinity, etc.), rheological behaviour such as yield stresses and thixotropy, and how these properties develop over time. By linking these temporal changes due to sediment settling and consolidation processes, the research aims to identify critical thresholds for navigability.

The concept of circularity is used as an alternative to linear flow materials in order to protect the environment from potential damage. To determine to what extent a sediment management project contributes to circularity practices, it is necessary to quantify how much of the dredged material is maintained within the system. Hence, defining boundaries for the system and circularity indicators for dredged material plays a vital role in measuring the circularity level of a certain project [1]. This study concentrates on defining circularity indicators for sediment management projects when a certain amount of material is diminished during the pre-processing stage. Besides, the perspectives of different stakeholders (e.g. port authorities, and dredging contractors) influence the selection of strategies for circular maintenance dredging [2].

Inland waterway transport (IWT) is increasingly recognized as a cleaner, more efficient alternative to road transport for freight movement. However, the successful adoption of zero-emission fuelsparticularly hydrogen and battery power-depends on the strategic location and capacity of bunkering and charging stations. This extended abstract presents a multi-stage framework that combines simulation and mixed-integer optimization to identify where and how these stations should be deployed. First, a simulation model estimates the fuel consumption of vessels under varied waterway conditions, vessel dimensions, and hydrodynamic influences. Next, an optimization module, modeled within the supply chain, aims to minimize capital and operating expenses while ensuring sufficient fuel availability. Strategically placing multi-fuel stations in high-demand locations reduces infrastructure redundancy and ensures flexible operations. This study underlines the critical role of well-planned bunkering infrastructures and highlights the potential for future expansions in zeroemission vessel networks.

Purpose: Maintenance dredging can often hinder port operations resulting in waiting times for seagoing vessels. The purpose of this paper is to investigate the dynamics between maintenance dredging activities and seagoing vessels, specifically focusing on how waiting times can be reduced. Then, the role of selecting different maintenance dredging strategies in reducing these waiting times is outlined. Methods: The study analyzes historical automatic identification system (AIS) data to identify the interaction between maintenance dredging and seagoing vessels and quantify the hindrance periods for the Mississippihaven case study in the Port of Rotterdam, the Netherlands. The trajectories of the vessels are analyzed in a simple case to show how the vessels interact and how the waiting times are quantified. The interactions are checked with the Port of Rotterdam for different port calls to ensure that maintenance dredging was the reason for these delays. Results: By analyzing the AIS data analysis of vessels in a given time window, the dredgers for maintenance work can be identified and their activities within or near the terminal can be determined. In addition, the waiting time of the seagoing vessel caused by the maintenance dredging is quantified at the terminal entrance. Conclusion: The study discusses how the maintenance dredging operations could be improved by adjusting the loading and sailing phases of maintenance dredging and provides some theoretical and managerial insights. Alternative port maintenance strategies to minimize the waiting time caused by the hindrance are also discussed.

Ports and waterways are key in supporting the waterborne supply chains that form the backbone of global trade. Maintaining adequate water depth is vital for accessibility and safe navigation. Port authorities and contractors are the key players in developing maintenance strategies, and they strive for a mutually beneficial compromise. Port authorities aim to optimize port performance while keeping costs and delays at acceptable levels. Contractors aim to optimize the use of equipment and execution strategies to achieve cost-effectiveness and time efficiency. While minimum cost and duration are common and simple decision criteria, there is growing societal pressure to incorporate smart, sustainable, and circular elements. However, these elements are less straightforward to interpret and there is a lack of a comprehensive framework to quantify smart, circular, and sustainable strategies. This lack of clarity presents significant challenges in balancing traditional and emerging objectives in port maintenance. Our study directly addresses this gap by providing a structured approach to decision-making that integrates these critical but complex elements. As a result, trade-offs on these important issues are harder to achieve reducing the contributions of port authorities and contractors. This study addresses this gap by applying the Frame of Reference (FoR) method to extract objectives and indicators for decision-making from both the port authorities' and contractors' perspectives. We fill in the prescribed elements of the basic FoR template through a systematic literature review (SLR), clarifying to what extent consensus exists on these topics. The SLR revealed 128 articles and identified common strategies, research methods, influential journals, and contributing countries. Projecting these findings onto the basic FoR template showed that the protection of marine ecosystems and sediment management has received considerable attention from researchers while mitigating emissions and adopting smart techniques are emerging subjects in the literature that need further investigations. As a result, this study offers theoretical and managerial insights to improve what can be achieved with smart, circular, and sustainable maintenance strategies, while identifying crucial remaining knowledge gaps.

Purpose
Recirculation dredging is a port maintenance concept developed in the Port of Emden, Germany to create a navigable fluid mud layer. This study investigates the effects of recirculation on key sediment properties, including density, yield stress, and oxygen concentration.

Methods
Six field monitoring surveys were carried out at two locations at different times of the year to assess changes before and after recirculation. Bathymetry, bulk density, yield stress, and oxygen concentration profiles were measured in situ. The settling properties and oxygen concentration levels on collected fluid mud samples were analyzed in the laboratory.

Results
The investigation reveals minimal changes in the density of recirculated fluid mud. However, the post-recirculation measurements showed a decrease in yield stress, ranging from 18 to 51% at Große Seeschleuse (GS) and 36% to 52% at Industriehafen (IH). The yield stress and density vary depending on the frequency of dredging. After structural density (1166 kg m−3 in GS and 1173 kg m−3 in IH), the yield stress of fluid mud increased exponentially. Therefore, monitoring of the yield stress is important for recirculation. A slight increase in oxygen concentration was observed post-recirculation, especially during winter. Yet, the rapid decline in oxygen levels post-mixing in the laboratory showed that sustaining long-term elevated oxygenation levels is not feasible by recirculation dredging alone.

Conclusions
The findings highlight the effectiveness of the recirculation on the yield stress, density, and oxygen concentration of fluid mud and illustrate the importance of considering both density and yield stress in sediment management practices. Future research should address the temporal evolution of density, yield stress, and oxygen levels following a dredging intervention and the influence of extracellular polymeric substances (EPS) and organic matter decay on sediment behavior.

For future strategies in water depth maintenance in the Port of Hamburg, determining the navigability limit (i.e., the safe nautical depth) is of major importance. For this purpose, the project Nautical Depth was set up at the Hamburg Port Authority. The aim of the project is to measure a safe nautical depth under various boundary conditions and to identify limits for a safe passage in port areas with fluid mud. Among other things, the project is conducted in close collaboration with the Port of Antwerp Bruges, the Port of Rotterdam, and TU Delft within the research platform MUDNET (www.tudelft.nl/mudnet).

To gain the necessary acceptance for a reassessment of the nautical depth, it is important to determine the rheological properties of the sediment in-situ. Several existing survey devices for monitoring nautical relevant rheological sediment properties have been tested. However, these devices cannot be used for spatial determination of rheological properties as they only provide cross-sectional measurements and depth profiles. Therefore, new evaluation algorithms were developed to correlate echo sounding data with in-situ rheological properties to ensure spatial coverage of a safe nautical depth.

As a first step, hydrographic surveys and sampling campaigns were carried out to provide system knowledge of the water column and the riverbed. Basic scientific research on the rheological behaviour of the fluid mud was also carried out. In a second step, the safe conditions for adapting the fluid mud layers at the berths for the nautical bottom concept were investigated and new nautical depth approaches were introduced at different locations in the Port of Hamburg. The next step was to analyse the effect of the fluid mud on the manoeuvrability of the ships. To this end, existing Computational Fluid Dynamics (CFD) models were extended to determine the non-linear effects and forces of non-Newton fluids on ship hull, rudder, and propeller efficiency. The results of the CFD model have been and are being validated with hydraulic model tests (scale 1:60) and in-situ measurements in the Port of Hamburg. In a final step, the results of the CFD model will be used to adapt the software of existing ship handling simulators. These simulations will be used to define the safe boundary conditions and limits for a new nautical depth for vessels to navigate through the fluid mud.

Coandă-effect-based collection stands out as the foremost technology in polymetallic-nodule mining due to the absence of direct contact between the collector and the ocean floor. Yet, this collection method disturbs the ocean floor, and minimizing such disturbance is crucial from an environmental viewpoint. To this end, a solid understanding of the interplay between the collector and the sediment bed is required. Therefore, we carried out a series of small-scale experiments, where a collector drives over a subaqueous clayey bed. These experiments provide the very first quantitative data on cohesive sediment erosion caused by a moving Coandă-effect-based collector, as well as on turbidity currents generated behind the collector head. This paper discusses the observations and findings derived from these experiments. Our findings reveal a logarithmic relationship between erosion depth and the flow impinging force applied on the clayey bed. An increased flow rate in the collection duct results in a slower turbidity current generated behind the collector head. This study enhances the ability to forecast sediment erosion caused by Coandă-effect-based collectors, offering the possibility to optimize the collector operational conditions and minimize the magnitude of the resulting sediment plumes.

The maximum packing fraction (φ_fm) of flexible fibers is an essential parameter for understanding the rheological behavior of flexible fiber-reinforced cement paste (FFRCP). However, direct measurement of φ_fm of flexible fibers is still lacking. In this study, a shear rheology-based method for direct measurement of φ_fm was proposed and the assumption of fiber conformation under shear was verified by micro-CT. Based on this, a yield stress model for FFRCP was constructed to explain the entanglement and friction effects in the fiber network. Finally, static yield stress tests and small amplitude oscillatory shear (SAOS) tests were carried out to explore the structural build-up of FFRCP. It was found that the proposed method enables direct determination of φ_fm through only a few viscosity-fiber content data for a given FFRCP. Furthermore, the proposed model can describe the static yield stress of FFRCP well. Finally, the relative structural build-up rate of FFRCP follows a similar trend as the relative yield stress, with a critical relative fiber volume fraction (0.299) as the boundary. Subsequently, the relative structural build-up gradually deviates from the relative yield stress due to the limiting effect of the fibers.

This article discusses whether or to what extent flocculation plays a role in the saline deep-sea environment and whether sediment plumes generated by deep-sea mining activities are affected by the process of flocculation. The results of our laboratory study demonstrate that deep sea mineral clay with a median floc size of 20 μm can flocculate quickly within 2.5 min of mixing to form flocs with a median floc size of about 50–150 μm and outliers as large as 500 μm in size due to the presence of natural organic matter. At high shear (turbulent mixing), a threshold of about 125 s−1 was found above which, organic matter can successfully bind to clay. Above 125 s−1, the steady-state floc size is also found to increase linearly with shear. In low energetic conditions (when flocs experience mainly differential settling), the median floc sizes are found to be 2 or 3 times larger than at turbulent mixing. As expected, the rate of flocculation is greater at higher clay concentrations. At long mixing times, the median floc size is found to decrease due to the breaking/reconformation of flocs. Experiments performed to study the ageing of flocs at rest demonstrated that a dynamic process was ongoing between the organic matter and the clay. It is hypothesized that the organic matter present has amphiphilic properties. Over time, the organic matter would rearrange itself such as to maximize its contact area with the mineral clay, resulting in two effects, depending on the structure of the flocs. In the case of flocs formed at high shear, it led to a rupture of flocs. A slow agitation of settled flocs, having previously experienced low shear conditions, on the other hand, led to aggregation. Overall, the results found in the present article show that flocculation likely plays a significant role in deep-sea areas.

In this work a high-magnification digital video camera in combination with a settling column is used to study in a first part the influence of the amount of flocs transferred into the settling column on their settling velocity. In a second part, the setup was used to study the properties of flocs prepared at different clay concentrations but at same flocculant to clay ratio (2.5mgg−1). Illite clay was used and flocculated in a 1 L jar with an anionic polyacrylamide (flocculant). Results show that the average settling velocity of flocs is a function of the amount of transferred flocs. It was also found that floc size and settling velocity depend on clay concentration. This is attributed to the fast aggregation happening in the jar when flocculant and clay are mixed: at higher clay concentrations, larger flocs are created in the first minutes of the experiment, with low densities that prevent them from settling to the bottom of the jar.

Instead of maintenance dredging, an alternative option for port authorities is to adapt the PIANC's nautical bottom approach. For practical purposes, the nautical bottom is defined as the level at which the fluid mud reaches either a critical density or a critical yield stress (the shear strength). These values generally correspond to a level at which the mud undergoes a so-called "rheological transition", where the density and strength of the mud increase rapidly over a short distance. Below this level, the mud becomes more and more like solid ground and is therefore no longer navigable.
Recently, new scientific and practical research has been conducted in order to gain additional knowledge on navigability in ports with fluid mud layers. In particular, a systematic rheological analysis was conducted to determine the critical limits of the yield stresses and density of fluid mud. Furthermore, a Computational Fluid Dynamics (CFD) model was developed to numerically investigate the ship-mud interaction. The model was applied to study the effects of muddy bottoms on the full-scale resistance of a modern oil tanker at speeds between 3 and 9 knots. It was confirmed that not only the density but also the yield stress of the fluid mud should be considered in the practical application of the nautical bottom. Finally, the paper discussed how the standard maintenance dredging methods can be used for producing navigable fluid mud layers.

Reducing waiting times is crucial for ports to be efficient and competitive. Important causes of waiting times are cascading interactions between realistic hydrodynamics, accessibility policies, vessel-priority rules, and detailed berth availability. The main challenges are determining the cause of waiting and finding rational solutions to reduce waiting time. In this study, we focus on the role of the design depth of a channel on the waiting times. We quantify the performance of channel depth for a representative fleet rather than the common approach of a single normative design vessel. The study relies on a mesoscale agent-based discrete-event model that can take processed Automatic Identification System and hydrodynamic data as its main input. The presented method’s validity is assessed by hindcasting one year of observed anchorage area laytimes for a liquid bulk terminal in the Port of Rotterdam. The hindcast demonstrates that the method predicts the causes of 73.4% of the non-excessive laytimes of vessels, thereby correctly modelling 60.7% of the vessels-of-call. Following a recent deepening of the access channel, cascading waiting times due to tidal restrictions were found to be limited. Nonetheless, the importance of our approach is demonstrated by testing alternative maintained bed level designs, revealing the method’s potential to support rational decision-making in coastal zones.

Abstract: Efficient port operations require minimizing turnaround time which is the total duration of a vessel's stay in the port and encompasses waiting, maneuvering, berthing, and de-berthing times. The turnaround time can be reduced by optimizing arrivals and departures, maximizing berth availability, facilitating cargo handling, and maintaining water depth. Maintenance dredging, the primary method for maintaining water depth, is used as a continuous activity to ensure the available water depth is sufficient for the navigation of commercial (seagoing, inland, barges, etc.) vessels. The continuity of maintenance dredging interferes with commercial vessels that aim to be served in terminals. Despite the cost imposed on port authorities due to these interferences, addressing this challenge in a structured way is overlooked. To fill this gap, an open-source discrete-event model is presented in this study that employs agent-based simulation to model the interaction between seagoing and maintenance dredging processes. A simple case is proposed to provide an example of how this interaction is simulated. Then, the implications and limitations of this study are discussed and the directions for future research are recommended.

The presence of mud layers on the bottom of ports and waterways can have negative effects on the hydrodynamic behaviour of marine vessels. This numerical study investigates the effect of muddy seabeds on the full-scale resistance of an oil tanker sailing straight ahead. The objective is to determine the influence of factors such as the densimetric Froude number, UKC and mud rheology at speeds between 3 and 9 knots. The numerical study is conducted using a finite-volume Reynolds-Averaged Navier–Stokes (RANS) flow solver combined with the Volume-Of-Fluid (VOF) method to capture the mud–water interface. At certain critical speeds, the presence of mud increased the ship’s total resistance by up to 15 times compared to the case with solid bottoms. The non-Newtonian rheology of mud was found to influence the ship’s resistance mainly at low speeds and when sailing through the mud layer. This article also shows that, when sailing through mud, the computed resistance at high speeds may be underestimated because of two effects, namely ‘water lubrication’ and ‘numerical ventilation’.